List of Seminar


[300] Topic: Observational properties of type Iax supernova

Speaker: Mridweeka Singh
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-12-15
Time: 15:30hr
Venue: Aries Auditorium

Abstract: Type Iax supernovae (SNe) are a subclass of type Ia SN with exceptionally different features. These are low luminous and less energetic events without a secondary NIR peak. We discuss here mainly on the observational properties of these peculiar events. They do not follow a typical trend of colour evolution, their spectral diversity is most noticeable feature amongst all the observational properties. They form a link between their spectral diversity at late times with their explosion scenario.


About Speaker: SRF at ARIES



[298] Topic: Study of Magnetized Accretion Flow With Relativistic Equation of State

Speaker: Kuldeep Singh
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-12-14
Time: 15:30hr
Venue: Aries Auditorium

Abstract: We study magnetized accretion shock flows using the relativistic equation of state having variable adiabatic index (Γ). We include bremsstrahlung and cyclotron cooling for the neutron star which has very strong dipole-like magnetic field and is aligned with the rotation axis of the star. We find all possible accretion solutions. All accretion solutions terminate with a shock very near to the star surface and the height of this primary shock does not vary considerably either with the spin period or the Bernoulli parameter of the flow, although the strength of the shock may vary with the period. For moderately rotating central star there is a possible formation of multiple sonic points in the flow and there a second shock far away from the surface of the star. We find that if the rotation period is less than a certain value, then multiple critical points or internal shocks are not possible, but this value depends upon the composition of the flow. We also find that cooling effect dominates after the shock and for consistent accretion solutions cyclotron cooling should be present along with the bremsstrahlung cooling.


About Speaker: SRF at ARIES



[299] Topic: Type Iax SUPERNOVAE: A new sub-class of type 1a Supernovae

Speaker: Pankaj Sanwal
Affiliation: ARIES Auditorium
Date (yyyy-mm-dd): 2017-12-14
Time: 11:30hr
Venue: ARIES Auditorium

Abstract: Type Iax supernovae (SNe Iax) are proposed as one new sub-class of SNe Ia since they present observational properties that are sufficiently distinct from the bulk of SNe Ia. SNe Iax are the most common of all types of peculiar SNe by both number and rate, with an estimated rate of occurrence of about 5%–30% of the total SN Ia rate. The progenitor system and explosion model that best fits all of the data is a binary system of a C/O WD that accretes matter from a He star and has a deflagration. At least some of the time, this explosion will not disrupt the WD. However, the progenitor systems of SNe Iax are still uncertain.


About Speaker: SRF at ARIES



[296] Topic: “X-ray Flux and Spectral Variability of Six TeV Blazars with NuSTAR”

Speaker: Ashwani Pandey
Affiliation: ARIES Nainital
Date (yyyy-mm-dd): 2017-12-13
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: We report on the results of timing and spectral studies of Nuclear Spectroscopic Telescope Array (NuSTAR) observations of six TeV emitting high frequency peaked blazars: 1ES 0347−121, 1ES 0414+009, RGB J0710+591, 1ES 1101−232, 1ES 1218+304 and H 2356-309. Two out of six TeV blazars have shown strong evidences of intraday variations in 3–79 keV energy range. We also found hint of intraday variability timescale of 23.51 ks in 1 LC of 1ES 1218+304 using autocorrelation function analysis. We obtained magnetic field B ∼ 0.03 G, electron Lorentz factor γ ∼ 2.16 × 10 6 and emission region size R ∼ 1.19 × 10 16 cm for 1ES 1218+304 using the variability timescale. The other blazars LCs do not show any variability timescales shorter than their observation lengths, however, data were both noiser and sparser for them. We also investigated the spectral shape of these TeV blazars and found that the spectra of 1ES 0414+009 is well described by the single power-law with photon index Γ ∼ 2.77. The spectra of other five HBLs are better represented by log-parabola model with local photon index (at 10 keV) α ∼ 2.23 − 2.67 and the curvature β ∼ 0.27 − 0.43.


About Speaker: SRF at ARIES



[294] Topic: EVOLUTION OF STARS- LIFE STAGES OF DIFFERENT MASS STARS

Speaker: Jayanand Maurya
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-12-05
Time: 15:30hr
Venue: New Auditorium

Abstract: The process of change that a star undergo during its life-time is called the stellar evolution. The primary factor determining how a star evolves during its life-time is its mass at the time when it reaches the main sequence. From evolution point of view stars can be divided in mainly 3 types- high mass stars (M > 8 M_sun), intermediate mass stars (8 M_sun > M > 2 M_sun ), and low mass stars (M < 2 M_sun). In this talk I will brie y discuss the evolution, through various life-stages, of different mass stars.


About Speaker: Jayanand Maurya is a research scholar in ARIES. This is a Tuesday Seminar.



[293] Topic: Fossil fuel vs wood burning sources of black carbon over Panchgaon, south Delhi outskirts

Speaker: Dr. U C Dumka
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2017-11-29
Time: 15:30hr
Venue: Auditorium

Abstract: The current work is based on year-long measurements (April 2015 – March 2016) of continuous BC mass concentrations via Aethalometer-42 taken at a rural site in the southern Delhi outskirts and focuses on analyzing the BC temporal evolution and evaluating the contributions from BCff and BCwb to the total BC mass on daily, monthly and seasonal basis. This is the first time that a BC source-apportionment study is attempted at the Delhi outskirts (~50 km away from the city center), and the results are compared with those performed over urban environments in India (Delhi, Ahmedabad, Gorakhpur).


About Speaker: Speaker is Scientist in ARIES, Nainital



[291] Topic: Fossil fuel vs wood burning sources of black carbon over Panchgaon, south Delhi outskirts

Speaker: Dr. Sarvan Kumar
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2017-11-17
Time: 15:30hr
Venue: Auditorium

Abstract: The current work is based on year-long measurements (April 2015 – March 2016) of continuous BC mass concentrations via Aethalometer-42 taken at a rural site in the southern Delhi outskirts and focuses on analyzing the BC temporal evolution and evaluating the contributions from BCff and BCwb to the total BC mass on daily, monthly and seasonal basis. This is the first time that a BC source-apportionment study is attempted at the Delhi outskirts (~50 km away from the city center), and the results are compared with those performed over urban environments in India (Delhi, Ahmedabad, Gorakhpur).


About Speaker: Dr. Sarvan Kumar is a post-doctoral fellow at ARIES. He is working on atmospheric aerosols and its radiative and climatic impact.



[290] Topic: Accretion theory around compact objects

Speaker: Shilpa Sarkar
Affiliation: ARIES, Manora
Date (yyyy-mm-dd): 2017-11-14
Time: 15:30hr
Venue: Auditorium

Abstract: Accretion is the process by which a body aggregates matter from its surroundings due to its strong gravitational potential. It is the most efficient means known till now for liberating energy. It is believed to power binary systems, active galactic nuclei etc. My discussion therefore centres on the development of accretion theory and its applications in astronomical objects. During this I will focus mainly on two important models of accretion which are the corner stones in the development of accretion theory – 1) Spherical accretion onto a compact object and the 2) Shakura Sunyaev disk model.


About Speaker: PhD scholar



[289] Topic: Optical Variability of the Peculiar TeV Gamma-ray AGN IC 310

Speaker: Dr. Alok C. Gupta
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2017-11-14
Time: 16:30hr
Venue: Auditorium

Abstract: We present results of the first optical monitoring of the peculiar Active Galactic Nucleus IC 310. We performed photometric observations in multiple optical passbands using two optical telescopes operated by Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, India between December 2014 and March 2015. IC 310 was found to be active throughout the monitoring period, displaying significant and apparently simultaneous flux variations in the optical B, V, R, and I passbands. Over this entire monitoring period we detected a progressive increase in the amplitude of variability with frequency with a range from 62.5% in the I band to 87% in B band. We briefly discuss various physical mechanisms likely to cause the observed variability of IC 310.


About Speaker: Speaker is Scientist in ARIES, Nainital



[282] Topic: SN 2015as: SN 2015as: A low luminosity Type IIb supernova without an early light curve peak

Speaker: Anjasha Gangopadhyay
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2017-11-13
Time: 15:30hr
Venue: Auditorium

Abstract: Stripped envelope supernovae (SE-SNe) are the group of core-collapse SNe that strip off their outer Hydrogen envelopes due to high stellar winds or due to interaction with a binary companion where mass transfer occurs through a Roche lobe overflow. We present results of the photometric (from 3 to 509 days after the explosion) and spectroscopic (up to 230 days post explosion) monitoring campaign of a member of the subgroup, Type IIb supernova (SN) 2015as. The early light curve and colour evolution of SN 2015as suggests that SN 2015as belongs to the SN IIb subgroup that does not show the early, short-duration photometric peak. Bolometric light curve modelling infers a binary progenitor scenario. At 75 days after the SN explosion, its spectrum transitions from that of a SN II to a SN Ib. P Cygni features due to He I lines appear at around 30 days after explosion, indicating that the progenitor of SN 2015as was partially stripped. SN 2015as is one of the lowest velocity member of the subgroup implying that the explosion energy is used in expanding the ejecta resulting in a fainter primary peak.


About Speaker: SRF at ARIES



[284] Topic: A comparison of the soft X-ray photon index of broad and narrow-line Seyfert 1 galaxies

Speaker: Vineet Ojha
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-11-13
Time: 16:30hr
Venue: Auditorium

Abstract: We study the soft X-ray (0.1-2 keV) properties of a well-selected sample of 66 Narrow- line Seyfert 1 (NLSy1) and 53 Broad-line Seyfert 1 (BLSy1) galaxies observed by ROSAT in 0.1-2.0 keV energy band. A systematic homogeneous analysis is carried out to estimate their soft X-ray photon index (Γ X ) and its correlations with other parameters of nuclear activities such as Eddington ratio (R Edd ≡ L bol /L Edd ), bolometric luminosity (L bol ), black hole mass (M BH ) and the width of the broad component of Hβ line (FWHM(Hβ)). In our analysis, we found (i) the existence of bimodality of the Γ X, R Edd distributions among NLSy1 and BLSy1 galaxies, with a steeper Γ X for NLSy1 galaxies and (ii) a significant positive correlation between Γ X and R Edd for the sample of NLSy1 but non-significant for the sample of BLSy1. No significant correlation is found for Γ X -M BH, Γ X -FWHM(Hβ), while a moderate Γ X -L bol relation is present for the sample of NLSy1, though with a lower statistical significance than that between Γ X and R Edd. The observed significant Γ X -R Edd correlation for our NLSy1 galaxies ap- pears to be qualitatively similar to the luminous AGNs derived based on their hard X-ray photon index, which is generally consistent with the theoretical prediction of X-ray productions by a disc-corona system.


About Speaker: SRF at ARIES



[286] Topic: STUDY OF BLUE STRAGGLER STARS IN GALACTIC GLOBULAR CLUSTER NGC 6656

Speaker: GAURAV SINGH
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-11-10
Time: 03:30hr
Venue: AUDITORIUM

Abstract: Being one of the oldest stellar systems, Globular clusters offers an excellent opportunity to understand the dynamical evolution of the cluster. NGC 6656 is a Galactic globular cluster located at a distance of about 3 kpc. The nature of its formation and evolution has been debatable over the years. I will present the study of Blue straggler stars present in the cluster and will explain about the dynamical evolution of the cluster.


About Speaker: PhD Scholar at Aries



[285] Topic: Atmospheric Science Activities at the National Astronomical Research Institute of Thailand (NARIT)

Speaker: Dr. Ronald Macatangay
Affiliation: Atmospheric Research Unit, NARIT, Chiang Mai, Thailand
Date (yyyy-mm-dd): 2017-11-09
Time: 15:30hr
Venue: Auditorium

Abstract: The National Astronomical Research Institute of Thailand (NARIT) has recently began to establish the National Research Center for Atmospheric Science (October 2016 – present). It focuses on studying: (1) space weather impact on Earth’s climate and the upper atmosphere; (2) impacts of the lower atmosphere on the upper atmosphere and vice versa; and (3) effects of greenhouse gases, air pollutants and aerosols on climate, weather and health. In this talk, initial research on air pollutant concentrations will be presented, specifically: (1) non-chemistry coupled modeling of PM10 over Chiang Mai, Northern Thailand; (2) chemistry coupled modeling of air pollutants over Thailand; (3) planetary boundary layer height temporal evolution and its relation to PM10 and PM2.5 concentrations. A potential aircraft campaign over the South/Southeast Asian region will also be discussed.


About Speaker: Dr. Ronald is leading the Atmospheric Research group at NARIT, Chiang Mai.He is visiting ARIES for future collaborative programs in the area of atmospheric Sciences.



[283] Topic: Cradle to grave: Analysis of September 6, 2017 solar event.

Speaker: Abha Monga
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2017-11-07
Time: 15:30hr
Venue: Auditorium

Abstract: The sun emitted two significant X-class flares on September 6, 2017 from NOAA AR 12673. The second X9.3 class flare was most powerful in more than a decade. At 09:10 UT, an X-class solar flare — the most powerful sun-storm category — blasted from a large sunspot on the sun's surface, was the strongest since 2015, at X2.2, but it was dwarfed just 3 hours later, at 12:02 UT, by an X9.3 flare. X-class solar flares can cause radiation storms in Earth's upper atmosphere and trigger radio blackouts. The debris from monster X9-class solar flare reached Earth and severe G4-class geomagnetic storm.


About Speaker: Ph.D. Scholar



[279] Topic: On the incidence of MgII absorbers along the blazar sightlines

Speaker: Sapna Mishra
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-11-06
Time: 15:30hr
Venue: Auditorium

Abstract: It is widely believed that the cool gas clouds traced by MgII absorption, within a velocity offset of 5000 kms−1 relative to the background quasar are mostly associated with the quasar itself, whereas the absorbers seen at larger velocity offsets towards us are intervening absorber systems and hence their existence is completely independent of the background quasar. Recent evidence by Bergeron et al. (2011, hereinafter BBM) has seriously questioned this paradigm, by showing that the number density of intervening MgII absorbers towards the 45 blazars in their sample is nearly 2 times the expectation based on the MgII absorption systems seen towards normal QSOs. Given its serious implications, it becomes important to revisit this finding, by enlarging the blazar sample and subjecting it to an independent analysis. Here, we first report the outcome of our re-analysis of the available spectroscopic data for the BBM sample itself. Our analysis of the BBM sample reproduces their claimed factor of 2 excess of dN/dz along blazar sightlines, vis-a-vis normal QSOs. We have also assembled a ∼3 times larger sample of blazars, albeit with moderately sensitive optical spectra. Using this sample together with the BBM sample, our analysis shows that the dN/dz of the MgII absorbers statistically matches that known for normal QSO sightlines. Further, the analysis indicates that associated absorbers might be contributing significantly to the estimated dN/dz upto offset speeds ∆v ∼ 0.2c relative to the blazar.


About Speaker: SRF at ARIES



[281] Topic: Relativistic Jets: Processes Powering Broadband Emission and Locations of Emission Region

Speaker: Dr. Pankaj Kushwaha
Affiliation: University of Sao Paulo, Brazil
Date (yyyy-mm-dd): 2017-11-01
Time: 15:30hr
Venue: Auditorium

Abstract: Physical processes powering the broadband emission from relativistic jets and the location of emission region are two important questions in current exploration of jet physics. For the former, studying the statistical characteristics: flux histogram, flux variation with excess variability (rms-flux) and power spectral density (PSD) of the long term gamma-ray emission from AGNs consisting of 3 blazars and a radio-galaxy, we show that blazars’ flux histograms are log-normal while neither Gaussian nor log-normal describes the radio-galaxy. Irrespective of histogram, the excess-variability scales linearly with the flux (rms-flux) while the PSD is consistent with a shot noise process. These properties are similar to the statistical properties of X-ray emission from the solar corona and with the theoretical study of randomly oriented, magnetic reconnection powered minijets-in-a-jet model, thereby favoring magnetic-reconnection as the main driver. In the second part, studying the temporal evolution of the spectra from the blazar OJ 287, which probably host a binary system of SMBHs, we show that the gamma-ray spectra changes in accordance with the appearance of a strong accretion disk emission and broad line region (BLR). The results imply that most of the jet emission is occurring on sub-parsec scales, thereby suggesting that most of the jet energy is dissipated into particles within sub-parsec scales, if it was magnetically dominated in the beginning.


About Speaker: Dr. Pankaj Kushwaha has done Ph.D. from TIFR, Mumbai in 2015 and currently a postdoctoral fellow at University of Sao Paulo, Brazil. He works on multi-wavelength blazar variability and emission modeling.



[280] Topic: An introduction to type 1a Supernovae

Speaker: Pankaj Sanwal
Affiliation: ARIES, NAINITAL
Date (yyyy-mm-dd): 2017-10-31
Time: 15:30hr
Venue: AUDITORIUM

Abstract: Supernovae are exploding stars, the very final stages of evolution for some stars, that release tremendous energy. All supernovae are produced via one of two different explosion mechanisms i.e. the core-collapse of massive star and the thermonuclear explosion of a white dwarf which has been accreting matter from a companion. Supernovae of Type Ia, deprived of hydrogen and rich in heavy elements, play important roles in diverse areas of astrophysics from the chemical evolution of galaxies to observational astronomy. These are the thermonuclear explosions of white dwarfs accreting mass to reach the Chandrasekhar limit, they have homogeneous properties and are used as standardized candles. Photometry is the most easily acquired information about supernovae. The light curves constructed from regular imaging provide signatures not only for the energy input, the radiation escape, the local environment and the progenitor stars, but also for the intervening dust. They are the main tool for the use of the supernovae as distance indicators through the determination of the luminosity. The construction of bolometric light curves provides the most direct link to theoretical predictions. And an analysis of their spectra yields insights into the explosion mechanism.


About Speaker: PhD Scholar at ARIES



[276] Topic: A simple friction model for telescopes

Speaker: T S Kumar
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-09-26
Time: 12:00hr
Venue: Auditorium

Abstract: In this talk experimental characterization of friction in an astronomical telescope will be discussed followed by introduction of a new model for capturing the observed behaviour of friction in both the micro and macro displacement regimes of motion. The new model is a modification of the LuGre model but in comparison, it is simpler to implement and valid for velocity reversal systems like an astronomical telescope. The proposed model is represented with a pair of masses separated by a linear spring. This model is then employed to synthesize a feedback linearizable controller for the system. The simulation results for the proposed friction model in open loop are presented and validated with the experimental results. The stability aspect of the closed loop system with the modified friction model is then investigated. For estimating the unmeasurable states of the system used in feedback linearization, observability of the system with the new model for friction will be discussed.


About Speaker: Speaker is an engineer at ARIES.



[275] Topic: Magnetic activities in low-mass stars

Speaker: Subhajeet Karmakar
Affiliation: SRF
Date (yyyy-mm-dd): 2017-08-24
Time: 15:30hr
Venue: ARIES AUDITORIUM

Abstract: Late-type stars with a similar internal structure to that of the Sun, supposed to operate a similar type of dynamo mechanism. However, the observations of these stars have introduced a range of stellar rotation periods, gravities, masses, and ages, which put into the debate on the existing magnetic dynamo theory. In order to provide useful constraints for the dynamo theory, I propose to carry out an in-depth study of the stellar surface and the outer atmosphere of the active low-mass stars using X-ray, FUV, NUV, optical, and NIR observations. I intend to study the highly time-resolved correlation of photosphere, upper chromospheric and coronal activity indicators, the rotational modulation, surface inhomogeneity, surface differential rotations, and flaring events. Study of these observational evidences of magnetic activities will be very useful to yield insight into the nature of the associated magnetic dynamos. I propose for three projects on which I like to work on during the given time-span at ARIES. For my study, I will use ARIES and national facilities. The multi-band study will help us to understand the magnetic activity on mid-M-dwarf which is not well explained by current magnetic dynamo theory. We have observed active binary CC Eri using ASTROSAT satellite in November 2016. Simultaneous observations in UV and X-ray would give us the chromospheric and coronal features of the binary system. Whereas, the time-resolved spectral analysis will allow us to investigate origin and mechanism of the emission of radiations in this system. We have investigated BLP on G-K dwarfs and found that the linear polarization in a majority of active dwarfs are due the combined effect of magnetic intensification and scattering, where the degree of polarization is strongly correlated with various activity parameters, especially at the blue end of the optical electromagnetic spectrum. There are only a few observations in the literature of BLP for the RS CVn stars. Therefore, making use of AIMPOL mounted on 1.04-m ARIES ST, we would like to do a similar study for evolved RS CVn binaries, which will provide important constraints to understand the magnetic activities in evolved stars.


About Speaker: SRF



[270] Topic: Radiatively driven relativistic jets in curved space-time

Speaker: Indranil Chattopadhyay
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-08-11
Time: 15:30hr
Venue: New Auditorium

Abstract: We carry out a general relativistic study of radiatively driven fluid jets around black holes and investigate the effects and significance of radiative acceleration, as well as radiation drag. We apply relativistic equations of motion in curved space-time for the jet, plying through the radiation field of the accretion disc. Radiative moments were computed using the information of curved space-time. Slopes of physical variables at the sonic points are found using L'Hospital's rule and employed Runge-Kutta's $4^{th}$ order method to solve equations of motion. The analysis is carried out, using the relativistic equation of state of the jet fluid. The terminal speed of the jet depends on how much thermal energy is converted into jet momentum and how much radiation momentum is deposited on to the jet. Jets with terminal Lorentz factors up to $\gamt\sim 3$ are obtained for high energy electron-proton jets under intense radiation field. Moderate terminal speed $v_{\rm \small T} \sim 0.5$ is obtained for moderately luminous discs. Lepton dominated jets may achieve $\gamt \sim 10$. Many classes of jet solutions with single sonic points, as well as, radiation driven internal shocks are obtained. Along with terminal speeds, behaviour of physical quantities of the jets with distance is also studied. Variety of jet solutions are obtained, due to the interaction of accretion disc radiation with the out-flowing jet, where the possibility of moderate jets to relativistic jets is possible depending on the intensity of the radiation field and the energetics of the jet. We establish that radiation field is able to induce steady shocks in jets, one of the criteria to explain high energy power law emission observed in spectra of is some of the astrophysical objects.


About Speaker: Scientist E in ARIES.



[267] Topic: UNDERSTANDING GALACTIC STRUCTURE THROUGH OPEN STAR CLUSTERS

Speaker: Sreepriya V
Affiliation: Amrita Vishwa Vidyapeetham, Kerala
Date (yyyy-mm-dd): 2017-07-20
Time: 10:00hr
Venue: lecture room

Abstract: Star clusters are considered as building blocks of galaxies. Study of such stellar clusters is important for understanding the galactic structure and its chemical evolution. The project is aimed at understanding Galactic structure through open star clusters. Based on a large sample of Galactic open star clusters, with known parameters, we did statistical analysis of various cluster parameters. We studied in detail, the metallicity of clusters to get some understanding on the chemical evolution of the Galaxy.


About Speaker: She is Indian academy selected summer project student for 2 months



[269] Topic: Optical light curves of a type Ia supernova ASASSN-15qc

Speaker: Akriti Sinha
Affiliation: NIT Jamshedpur
Date (yyyy-mm-dd): 2017-07-20
Time: 10:15hr
Venue: Auditorium

Abstract: Supernova are fascinating objects to study due to the enormous amount of energy it produces during explosion. We present BVRI CCD photometry of the supernova ASASSN-15qc, which appeared in the galaxy UGC 00402, obtained during 2015 October 03 to 2016 January 13. We present the multiband light curves of the supernova constructed using the data which were obtained by photometry and standard calibration. We also plot the light curves of SN 2003hx and 2003du for comparison and confirmed that it is a Type Ia supernova.


About Speaker: Akriti Sinha is an Indian Academy of Science summer project student working in ARIES for two months.



[265] Topic: X-ray observations of an IP RXJ 1712-2414

Speaker: Arti Joshi
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-07-07
Time: 11:30hr
Venue: ARIES AUDITORIUM

Abstract: We present analyses of archival X-ray data obtained from the XMM-Newton and Suzaku satellites of an intermediate polar RXJ 1712-2414. The X-ray variations occur at the spin and synodic periods, supporting the view that this is a disc-overflow accreting system. The X-ray spectrum is strongly absorbed by a dense material with an average equivalent hydrogen column density of ~5×1022 cm−2 , which partially covers ~46 % of the X-ray source. Using the Suzaku spectra in 0.3-50 keV energy range, which is well explained by two temperatures collisional equilibrium plasma emission models with its reflection from the cold matter, the post-shock temperature is estimated to be 26 keV. A soft X-ray excess is seen in the X-ray spectrum of RXJ 1712-2414 and well modeled by the black-body with an average temperature of 98 eV. The spin phase resolved spectroscopy of RXJ 1712-2414 in 0.3-10.0 keV energy range shows that the spectral parameters are phase dependent. The spin phase dependent softness ratio indicate that coverage of accretion curtains is variable. A strong fluorescent Fe Kalpha emission line is also detected with the large values of reflection component and equivalent width, indicating that this is due to the reflection from the WD surface. The central energy of Fe Kalpha appears to be red-shifted and found to be modulated with the WD rotation, where modulations are minimum around the spin minimum, indicating that the red-shifted line is originated from pre-shock accreting material via fluorescence.


About Speaker: SRF at ARIES



[264] Topic: Source apportionment of black carbon

Speaker: Dr U C Dumka
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-06-27
Time: 15:30hr
Venue: Auditorium

Abstract: The current presentation divided into two parts: Part-1: Air Pollution and BC source apportionment in Delhi region during a winter research campaign This deals with the temporal variation of BC and air pollutions. The special focus is given on the source apportionment of BC and evaluation of the contribution of fossil fuel and wood burning on the black carbon. Part-2: Fossil fuel and wood burning contribution to BC during winter: Influence of meteorology and boundary layer dynamics The second parts deal with the source identification of BC and role of meteorology and boundary layer dynamics.


About Speaker: Scientist at ARIES, Nainital



[262] Topic: Young stellar objects : tool to understand star formation process

Speaker: Rakesh Pandey
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2017-06-20
Time: 15:30hr
Venue: Auditorium

Abstract: The process of star formation constitutes one of the main problems of modern astrophysics. As compared to stellar evolution it is very ill understood problem. Young stellar object (YSO) denotes a star in its early stage of evolution. Census of young stellar objects (YSO), correlation of their physical properties with ionizing source/s and their spatial distribution in a molecular cloud, are some of the signatures used to study the time-scale and star formation processes in a given region. In this talk I will talk about the various kind of star formation mechanisms, particularly focusing on the star formation on the edge of HII regions, a brief introduction about the YSOs. I will conclude my talk with, how studying YSOs helps us to understand star formation process.


About Speaker: JRF at ARIES



[263] Topic: Statistics in X-ray spectral analysis

Speaker: Bharti Arora
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2017-06-20
Time: 16:15hr
Venue: Auditorium

Abstract: Statistics are needed at every step of a scientific analysis. Statistics allow us to make decisions, evaluate observations, models, formulate questions and proceed forward with further investigations. The main goal of X-ray data analysis is to learn more about the physical properties of a source. When the new data arrives, statistics are employed to quantify the measurements. Typically, a parameterized approach to model the data is taken wherein physical models with certain parameters (e.g. temperature and density of a hot medium emitting X-rays) are applied to the data. Finding and evaluating a model that best describes the observed data will be the focus of my talk.


About Speaker: JRF at ARIES



[253] Topic: Unveiling new population of Active Galactic Nuclei using deep multi-wavelength surveys

Speaker: Dr. Veeresh Singh
Affiliation: PRL, Ahmedabad
Date (yyyy-mm-dd): 2017-05-31
Time: 15:30hr
Venue: ARIES, auditorium

Abstract: Active Galactic Nuclei (AGN) studies have mainly been limited to the local Universe, but more sensitive observations in recent years allow us to unveil new population of AGN at distant Universe. Using our deep radio continuum surveys combined with auxiliary optical, IR surveys we discover a new population of AGN called--Infrared-Faint Radio Sources (IFRSs). These AGN are at the redshift of (z) ~ 2 – 4 and exhibit diverse properties in terms of their radio luminosities, sizes and spectra, indicating them to be radio-loud AGN at different evolutionary phases. The optical-to-MIR colors and their non-detection in the X-ray band suggest them to be AGN hosted in dusty-obscured-galaxies. The discovery of IFRSs has important implication on the models of galaxy evolution and in explaining the missing unresolved AGN population predicted by the Cosmic X-ray Background model. In this talk I shall also discuss the role of deeper surveys from telescopes operating at radio, optical, IR and X-ray wavelengths.


About Speaker: Dr. Veeresh Singh is faculty in Astronomy and Astrophysics Division of Physical Research Laboratory Ahmedabad. His research interest involves: (i) Multiwavelength study of Active Galactic Nuclei (AGN) (ii) Formation and evolution of AGN and their host galaxies (iii) Population of AGN at high-redshifts and their environments and (iv) Deep radio and ancillary surveys of extragalactic fields.



[257] Topic: LAXPC instrument : Its overview and the science that can be done

Speaker: Shilpa Sarkar
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2017-05-16
Time: 15:30hr
Venue: Auditorium

Abstract: LAXPC instrument : Its overview and the science that can be done ASTROSAT is India’s first dedicated multi-wavelength space satellite. It observes the universe in the optical, UV and X-rays ranging from soft to hard. One of the major payloads onboard ASTROSAT is LAXPC (Large Area X-ray Proportional Counter) which is mainly devoted to X-ray timing and spectral studies of astronomical objects having energy in the range 3-80 keV. This talk will have a brief overview of the instrument and the science that can be done with it.


About Speaker: Junior Research Fellow



[256] Topic: Variable stars and variability in open star clusters.

Speaker: Jayanand Maurya
Affiliation: ARIES, Manora Peak, Nainital
Date (yyyy-mm-dd): 2017-05-09
Time: 15:30hr
Venue: Auditorium

Abstract: A variable star is a star whose apparent brightness changes over a period of time. In this talk I will briefly discuss different types of variable stars and reasons for variability. A brief discussion on why to study variability in open star clusters and distance measurement using variable star.


About Speaker: JRF at ARIES



[255] Topic: Satellite Remote Sensing of Fires

Speaker: Prof Christopher Justice
Affiliation: University of Maryland
Date (yyyy-mm-dd): 2017-05-08
Time: 09:30hr
Venue: Ashwini Council Room

Abstract: A general overview of satellite product with a specific interest on the NASA Moderate Imaging Spectroradiometer (MODIS) data product will be presented. Detailed discussion will be made on the MODIS fire product.


About Speaker: Prof Christopher Justice is a Professor and Dept. Chairman of Geography at the University of Maryland. Currently, Prof. Justice is a Program Scientist for NASA Land Cover Land Use Change (LCLUC) Program. Most recently, he became the Co-Director for the Center for Global Agricultural Monitoring Research. Current research of Prof Justice is on land cover and land use change, the extent and impacts of global fire, global agricultural monitoring, and their associated information technology and decision support systems. Prof Justice received his Ph.D. from the University of Reading, United Kingdom, in 1977.



[251] Topic: Counting photons in the Universe: from extreme UV to far-IR

Speaker: Dr. Vikram Khaire
Affiliation: NCRA
Date (yyyy-mm-dd): 2017-04-27
Time: 15:30hr
Venue: ARIES auditorium

Abstract: The photons emitted by galaxies (from stars and accreting super-massive blackholes) generate an uniform background know as the extragalactic background light (EBL). The spectrum of EBL is an important quantity for studying several astrophysical problems. For example, in extreme UV regime, the EBL is essential to study the hydrogen and helium reionization, metal enrichment and thermal history of the intergalactic medium, and missing baryons at low-redshift. In optical to far-IR regime, the EBL gives insight into the propagation of the high-energy gamma rays emitted by distant sources. In this talk, speaker will discuss how to count photons and estimate the spectrum of the EBL, especially the theoretical and observational intricacies involved in it. Also, he will introduce the state-of-the-art EBL model and its applications to wide range of problems.


About Speaker: Dr. Khaire is visiting fellow at NCRA, and did his Ph.D from IUCAA. His research interest is: Intergalactic medium, Extragalactic background light, Hydrogen and helium reionization, Star formation history.



[252] Topic: Active Galactic nuclei: tool to probe the high-redshift Universe

Speaker: Priyanka Jalan
Affiliation: ARIES, Manora Peak, Nainital
Date (yyyy-mm-dd): 2017-04-25
Time: 15:30hr
Venue: Auditorium

Abstract: Active Galactic nuclei (AGNs) refers to the existence of energetic phenomena in the nuclei or central regions, of galaxies which cannot be directed to stars. In this talk, I will explain the factors which helps in distinguishing AGNs from stars and what lead to the Unification model of AGN. A brief overview of the optical spectrum of AGN will also be given. Finally, I will conclude with why are we interested to study such distant objects.


About Speaker: JRF at ARIES



[249] Topic: A new Catalog of Narrow Line Seyfert 1 Galaxies from the Sloan Digital Sky Survey Data Release 12

Speaker: Hum Chand
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-04-03
Time: 15:30hr
Venue: ARIES auditorium

Abstract: The talk will focus in general on AGN and particularly on the narrow-line Seyfert 1 (NLSy1) galaxies. On NLSY1, I shell focus on our recent new catalog we prepared using the Sloan Digital Sky Survey Data Release 12 (SDSS DR12) by carrying out systematic analysis through modeling of the host galaxy, AGN continuum and prominent emission lines of the spectra of all the 68,859 SDSS DR12 objects that are classified as QSO by the SDSS spectroscopic pipeline with z lt 0.8. Our new catalog contains a total of 11,101 objects which is about 5 times larger than the previously known NLSy1 galaxies till date. Their monochromatic luminosity at 5100AA is found to be strongly correlated with H-alpha, H-beta and [O III] luminosities. The optical Fe II strength in NLSy1 galaxies is about two times larger than the broad-line Seyfert 1 (BLSy1) galaxies. Their cross correlation with Radio(FIRST) and X-ray catalog, as well as impact of this new enlarged catalog for future AGN studies along with the key NLSY1 parameter and parameters cross-correlations will also be discussed. The full catalog will be available on line from APJS catalog pages in future, with all the extracted parameters.


About Speaker: Scientist ARIES



[246] Topic: Short period variable stars in young open cluster Stock 8

Speaker: Sneh Lata
Affiliation: ARIES
Date (yyyy-mm-dd): 2017-03-10
Time: 11:30hr
Venue: ARIES Auditorium

Abstract: Time series photometry of 49 short period variable stars in the cluster Stock 8 is presented. Thirteen main-sequence and 16 pre-main-sequence stars are found to be probable members of the cluster. The main-sequence stars are classified as slowly pulsating B stars, beta Cep and delta Scuti stars. Six main-sequence stars may belong to new class variables as discussed by Mowlavi et al. (2013) and Lata et al. (2014). The age and mass of identified pre-main-sequence stars are found to be < 5 Myr and in the range of 0.5


About Speaker: Paper presentation



[242] Topic: Calibration and Validation activities for Earth Observational Satellite

Speaker: Dr. A. K. Mathur
Affiliation: SAC Ahemadabad
Date (yyyy-mm-dd): 2016-11-23
Time: 10:30hr
Venue: ARIES Auditorium

Abstract: The presentation will cover a brief account of calibration and validation activities of various ISRO's Earth Observation satellites sensors and their products. These include Oceansat-1, INSAT-3D/3DR, SARAL, Megha-Tropiques, CARTOSAT and RISAT-1 etc. Also some of the instruments available for calibration and validation at permanent cal-val sites will also be discussed.


About Speaker: Dr A K Mathur is working at SAC, Ahmadabad. He is head of Calibration and Validation Department. He is one of the expert in retrieval of SST and Atmospheric Humidity Profile from Meteorological Satellite.



[236] Topic: X-RAY INTRADAY VARIABILITY OF FIVE TEV BLAZARS WITH NUSTAR

Speaker: Ashwani Pandey
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-09-20
Time: 15:30hr
Venue: Auditorium

Abstract: We have examined 40 NuSTAR light curves (LCs) of five TeV emitting high synchrotron peakedblazars: 1ES 0229+200, Mrk 421, Mrk 501, 1ES 1959+650 and PKS 2155−304. Four of the blazars showed intraday variability in the NuSTAR energy range of 3–79 keV. Using a structure function analysis we searched for intraday variability timescales in these LCs and found indications of several between 2.6 and 34.4 ks in five LCs of Mrk 421, and a timescale around 7.5 ks for one LC of Mrk 501. We also employed an auto correlation function analysis and found indications of very similar timescales during those six observations as well as hints of timescales in four additional observations of Mrk 421. The other three blazars’ LCs do not show any evidence for intraday variability timescales shorter than the lengths of those observations; however, the data was both sparser, and noisier, for them. The 22 LCs of Mrk 421 observed between July 2012 and April 2013 show that this source was in a quiescent state for an extended period of time and then underwent an unprecedented double peaked outburst while monitored on a daily basis during 10 – 16 April 2013. We briefly discuss models capable of explaining these blazar emissions.


About Speaker: SRF



[235] Topic: The galaxy life cycle: from activity to quiescence across cosmic times.

Speaker: Abhishek Paswan
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-08-24
Time: 15:30hr
Venue: Auditorium

Abstract: The aim of the discussion is to explain the evolution of galaxies from the blue cloud via the green valley to the red sequence throughout their lives. It is well established that the regulation in star formation in galaxies is the main key which derives galaxies from the blue cloud to the red sequence. In this respect, there are many mechanisms such as AGN feedback, strangulation process and other gas removal processes including ram pressure gas stripping and galaxy-galaxy interaction/merger, which regulate the star formation in galaxies and derive them towards the red sequence. The discussion will shed light on these mechanisms and their roles to explain the galaxy evolution.


About Speaker: SRF



[234] Topic: X-Ray Emission of Supernovae

Speaker: Anjasha Gangopadhyay
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-08-23
Time: 15:30hr
Venue: Auditorium

Abstract: Core collapse supernovae, due to interaction of the shock wave with the circumstellar medium, show emission in the X-ray wavelengths. X-ray emission occurs in supernova due to a prompt thermal burst, compton scattered gamma rays synthesised by the radioactive nucleids or due to the interaction of the shock with the circumstellar medium. X-Ray emission occurs during two phases : one early and one late (> 100 days) in the evolution of supernova. SN 1978K is one of the X-ray rich supernova with long lasting X-ray emission in the recent times. We present the X-ray spectral analysis of SN 1978K. The spectrum is best fit with a "dual vnei" model having variable elemental abundances. Our analysis shows the presence of two temperature plasma - one with a higher temperature and other with a lower temperature . We will briefly describe Chevalier-Fransson model and justify our results with this.


About Speaker: SRF



[233] Topic: DYNAMIC EVOLUTION OF SUPERNOVA REMNANTS

Speaker: Raya Dastidar
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-08-22
Time: 15:30hr
Venue: Auditorium

Abstract: Supernovae are cosmic explosions that mark the end of massive stars and inject a significant amount of energy to the ISM. After the initial shock breakout, the ejecta sweeps through the ISM and finally merges with the ISM. This may last for more than 100000 years. This dynamic evolution of the supernova remnants can be divided into different phases according to the physical processes that dominate during the evolution. I will discuss these phases in detail and show that by applying some reasonable assumptions the typical time scales, expansion velocities and sizes characterizing these phases can be approximately extracted.


About Speaker: SRF



[230] Topic: Detection of variable stars in M31 galaxy

Speaker: Mr. Rishikesh Gokhale
Affiliation: Mumbai University
Date (yyyy-mm-dd): 2016-08-04
Time: 11:00hr
Venue: Auditorium

Abstract: This project is aimed at finding Cepheids and short as well as long period variable stars in M31 galaxy by studying their photometric characteristics. The data for the present study was obtained from 1.04m Telescope at Manora Peak, Nainital. In this project, initially stars were categorised as pulsating or non-pulsating and their corresponding period is found out by plotting a Periodogram of Power density Vs Frequency using Lomb-Scargle method. Stars with period between 2-100 days were studied for characteristic matching of Cepheids. For this, Period-Luminosity plots for possible Cepheid candidates are made. Then those candidates are plotted on Colour-Magnitude Diagram (CMD) to check whether they lie within Cepheid instability strip within the photometric uncertaintyIn the present analysis, I found one population I Cepheid and one population II Cepheid along with 11 long period and 3 short period variable stars.


About Speaker: Mr Rishikesh Gokhale has done summer project sponsored by Indian Academy of Science.



[228] Topic: Studies of Ring Galaxy

Speaker: Dr. Alka Mishra
Affiliation: ARIES, Manora Peak, Nainital
Date (yyyy-mm-dd): 2016-08-02
Time: 15:30hr
Venue: Auditorium

Abstract: Ring galaxies are very interesting objects. Their most prominent feature is the lack of a typical spiral structure, replaced by a narrow, ring-shaped accumulation of gas and stars. Such a peculiar distribution of matter is believed to form during collision of a spiral, gas-rich small galaxy with a early-type one . For small impact collision generates a ring-shaped structure in the disk in which the stellar and gaseous material crowd together. Large impact collision produce crescent-shaped rings with an off-centred remnant nucleus. In both cases the ring contains many massive, relatively young blue stars, which are extremely bright. The central region contains relatively little luminous matter.


About Speaker: Working as a PDF at ARIES



[226] Topic: X-ray super-flares on CC Eri

Speaker: Subhajeet Karmakar
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-07-21
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: We present an in-depth study of two superflares detected on active binary system CC Eridani by Swift observatory. The first flare (F1) triggered the Burst Alert Telescope (BAT) in the hard X-ray band on 2008 October 16, whereas the second flare (F2) triggered BAT on 2012 February 24. The rise phases of both the flares were observed only with BAT, whereas the decay phase was observed simultaneously with X-Ray Telescope (XRT) and BAT. The e-folding decay time indicates a faster decay in hard X-ray band than in soft X-ray. The peak X-ray luminosity for flares F1 and F2 in the 0.3–50.0 keV energy band (excluding 10–14 keV band) reached up to 3×1032 and 5×10^31 erg s^−1, which is ∼3500 and ∼600 times more than the quiescent value, respectively and larger than any other previous flares observed on CC Eri. Spectral analysis indicates a presence of three temperature corona with first two plasma temperatures remain constant during the flares at ∼3 and ∼10 MK. The flare-temperature peaked at 342 MK and 119 MK for F1 and F2, which are ∼4 and ∼2 times more than the mini- mum value. The abundances peaked at 2.0 and 1.2 solar abundances, which is larger than a factor ∼11 and ∼7 than quiescent state value. Using hydrodynamic loop modeling we derive loop-lengths for both flares as 1.25±0.13×10^10 cm and 1.26±0.20×10^10 cm, respectively. The Fe Kα emission at 6.4 keV was also detected in the X-ray spectra, and we model the Kα emission feature as fluorescence from the hot flare source irradiating the photospheric iron. Our analysis indicates the flare location is in any one of the binary components withan astrocentric angle of ∼85–90◦ .


About Speaker: SRF at ARIES



[225] Topic: Role of "Radiation Driven Implosion" in Star Formation Process

Speaker: Piyali Saha
Affiliation: JRF
Date (yyyy-mm-dd): 2016-07-19
Time: 15:30hr
Venue: Auditorium

Abstract: Interstellar HII regions are formed through joint effects of the wind and ionizing radiation produced by one or more early type stars. In the early phase of HII region, a rapid R-type ionization front propagates out to the Stromgren radius. This ionisation front typically drives a shock into the initial cloud. The clouds will be compressed by the ionisation-shock front and eventually star formation takes place. This process is termed as 'Radiation Driven Implosion' and is considered to be responsible for sequential star formation. The way how the ionisation-shock front propagates into an initially spherical cloud and how star formation takes place in the RDI mode will be explained in the talk.


About Speaker: JRF at ARIES



[224] Topic: Study of CO2 and other trace gases using CRDS technique

Speaker: Krishna Anil Kedia
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-07-13
Time: 15:30hr
Venue: Auditorium

Abstract: Cavity Ring Down Spectroscopy (CRDS) technique has a wide range of applications in atmospheric sciences as this single instrument is capable of measuring different gases with very high accuracy and sensitivity. Observations of CO2, CO and CH4 are being made at Nainital using CRDS. The diurnal pattern of these trace gases is mainly influenced by upslope and downslope mountain winds which is an important phenomena in high altitude sites. The boundary layer processes and role of OH chemistry is also playing an important role.


About Speaker: Mr. Krishna is from IISER, Bhopal and pursuing BS-MS dual degree (2nd year). He is doing a project under SRFP of Academies.



[223] Topic: Effect of mountain induced atmospheric waves on the trace chemical species over Himalayan region

Speaker: Sweta Kumari
Affiliation: Indian School of Mines, Dhanbad
Date (yyyy-mm-dd): 2016-07-12
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: This report presents first and preliminary results on the ozone depletion due to mountain induced atmospheric waves. Analysis of plots from Microwave Limb Sounder(MLS) instrument onboard Aura (NASA's satellite) affirms our hypothesis that mountain waves play a crucial role in Himalayan region atmospheric chemistry.


About Speaker: Ms Sweta Kumari is Btech Environmental Engineering fourth year student at Indian School of Mines, Dhanbad and is doing a summer research fellows, Indian Academy of sciences in ARIES from May-July 2016



[221] Topic: Photometric Study Of CW leonis(IRC +10216 )

Speaker: Sankalp Mishra
Affiliation: Indian Institute Of Science Education And Research, Thiruvananthapuram
Date (yyyy-mm-dd): 2016-07-05
Time: 11:00hr
Venue: Auditorium

Abstract: I will be presenting my work on Photometric Study Of CW Leonis. This talk includes the correction of raw images for the error induced by the CCD and Aperture photometry is for target star (CW Leonis) and 5 comparison star (randomly selected) to find their flux for many apertures by using IRAF. By usual procedure, best aperture is selected and two comparison stars of similar brightness are chosen by examining the light curves.Light curves (differential magnitude Vs time) are successfully generated for target stars,for best two apertures and time period is calculated.


About Speaker: I am currently pursuing Integrated MS majoring in Physic and minor in Mathematics at IISER TVM.



[219] Topic: Time series CCD photometry of exoplanet corot 24b

Speaker: Aarushi Gupta
Affiliation: Amity University, Noida
Date (yyyy-mm-dd): 2016-06-30
Time: 11:00hr
Venue: Auditorium

Abstract: My talk is about detection and analysis of a transit in the light curves of the exoplanet corot 24b. I have done data reduction, aperture photometry and differential photometry for my analysis using IRAF.


About Speaker: Ms Aarushi Gupta is a Bsc physics honors second year student at Amity University, Noida and is doing a summer internship in ARIES from May-June 2016



[220] Topic: Photometric study of open cluster NGC1893

Speaker: Abinaya Swaruba
Affiliation: Christ College, Bangalore
Date (yyyy-mm-dd): 2016-06-30
Time: 11:30hr
Venue: Auditorium

Abstract: I will be presenting my work on photometric study of open cluster NGC1893


About Speaker: Summer Fellow, Indian Academy of Science



[216] Topic: A temporal and spectral study of GRB afterglows

Speaker: Atharva Rawte
Affiliation: D. G. Ruparel College Mumbai
Date (yyyy-mm-dd): 2016-06-28
Time: 11:00hr
Venue: Auditorium

Abstract: In this project, I have studied the Swift XRT light curves of long duration GRBs. The X-ray light curves show a variety of properties - some decaying with a single powerlaw and some showing a break in the light curves. Based on the estimated jet-break time, we estimate the energetics and opening angle of the GRBs.


About Speaker: Mr. Atharva Rawte is B. Sc. Second year student at D. G. Ruparel College, Mumbai and is pursuing the academy summer fellowship in ARIES from May-June 2016.



[214] Topic: Boundary layer evolution over the central Himalayas from Radio Wind Profiler and Model Simulations

Speaker: Dr Narendra Singh
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-06-24
Time: 15:30hr
Venue: Auditorium

Abstract: Investigation on the Time-evolution of Local Boundary Layer (LBL)is carried out over a mountain ridge at Nainital (79.5oE, 29.4oN, 1958 m amsl) in the central Himalayan region, using a Radar Wind Profiler (RWP) during November 2011 to March 2012, as a part of the Ganges Valley Aerosol Experiment (GVAX). The study is restricted to clear-sunny days, resulting in a total of 78 days of observations. The standard criterion of the peak in the signal-to-noise ratio (SNR) profile was found to be inadequate in the characterization of Mixed Layer (ML) top at this site. Therefore, we implemented a new criterion of SNR > = 6 dB for the characterization of the ML and the resulting estimations are shown to be in agreement with radiosonde measurements over this site. The daytime average (0500-1000 UTC) observed boundary layer height ranges from 440±197 m in November (late autumn) to 766±317 m above ground level (AGL) in March (early spring). The observations revealed a pronounced impact of mountain-topography on the LBL dynamics during March, when strong winds (> 5.6 m s-1) lead to LBL heights of 650 m during nighttime.These results are also utilized to evaluate WRM model for boundary layer.Sensitivity simulations using a Mixed Layer model (MXL/MESSy) were also carried out which indicated that the springtime overestimation of LBL would lead to a minor uncertainty in simulated surface ozone concentrations.


About Speaker: Narendra Singh is working as a Scientist in the Atmospheric Science Group.



[261] Topic: Pre-main sequence evolution of low mass stars

Speaker: Tirthendu Sinha
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2016-06-14
Time: 15:30hr
Venue: Auditorium

Abstract: Stars go through different processes during their pre-main sequence evolution. Stellar parameters like radius, temperature, density etc. suffer drastic changes in different stages. Molecular clouds of few thousand astronomical unit(AU) contract to form stars of the size of fraction of AU whereas the temperature rises from 10-50 K to the order of 10^6 K and density increases ~10^20 times. I will mainly discuss different mechanisms that drive the process of contraction and finally forms a main sequence star.


About Speaker: JRF at ARIES



[191] Topic: Multi-wavelength Studies of Blazars

Speaker: Ashwani Pandey
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-06-13
Time: 15:45hr
Venue: Auditorium

Abstract: We present here the work done by us in last one year and also our future plans. We are working on two projects : radio to optical cross-correlation study of the blazar PKS 2155-304 and the x-ray intra-day variability of blazars with Nuclear Spectroscopic Telescope Array (NuSTAR). In the optical part of our first project we generated ~ 12 years optical R-band light curve of the blazar PKS 2155-304. By using the structure function (SF) and the auto- correlation function (ACF), we found eight possible periods which indicate two possibilities: an optical periodicity of ~ 311 days and multiple periods with their harmonics. We also generated more than three dozen light curves of blazars using NuSTAR data. We performed SF analysis and also estimated excess variance for these light curves.


About Speaker: Mr. Ashwani Pandey is a 2nd year student working with Dr. Alok C. Gupta.



[194] Topic: Spectro-Photometric Study of Star Forming Galaxies

Speaker: Abhishek Paswan
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-06-10
Time: 14:30hr
Venue: Auditorium

Abstract: In this thesis, our aim is to understand and constrain star formation in different types of galax- ies. For our study, we have chosen two samples – (i) A sample of late-type galaxies having recent and active star formation. (ii) A sample of early-type galaxies which are normally believed to be quiescent galaxies. Both the samples are selected from SDSS (Sloan Digital Sky Survey). We present here – (1) Data analysis of 20 late-type galaxies with their star formation rate (SFR) and Hα mor- phology using 1.3-m Devasthal telescope. (2) A detailed study of nuclei of Mrk 22 (Blue compact dwarf galaxy) in spectroscopy using 2-m HCT. (3) Constraining very low-level SFR in a sample of early-type galaxies using 1.4-GHz radio continuum data from VLA.


About Speaker: Mr. Abhishek is a 5th year student working with Dr. Amitesh Omar



[195] Topic: Study of Galactic Star Forming Regions and related Instrumentation

Speaker: Ms. Neha Sharma
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-06-10
Time: 15:45hr
Venue: Auditorium

Abstract: My thesis is divided into two parts: Part-I The main theme of this part is a) To study the characteristic properties of triggered star formation due to cloud-cloud collision and radiation driven implosion processes using optical polarimetry and molecular lines (12CO, C18O, HCN and N2H+) observations. b) To study the accretion properties of young stellar objects associated with the bright-rimmed clouds using near-IR spectroscopy. c) To study the dust and gas properties of λ-Ori HII using multi-wavelength optical polarimetry, Planck and WISE archival data. Part-II The main theme of this part is to develop a) A complete Zemax design of a wide field optical polarimeter to be used with 1.3m telescope - WiFi-Pol. b) A pipeline software in python that can be used to reduce polarimetric data of AIMPOL and WiFi-Pol.


About Speaker: Ms. Neha is a 5th year student working with Dr. Maheswar G.



[192] Topic: MHD Outflows and Accretion Model with Fixed and Variable Gamma Equation of State

Speaker: Kuldeep Singh
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-06-06
Time: 10:30hr
Venue: Auditorium

Abstract: We study MHD outflows with variable adiabatic index. We then find proper boundary conditions for accretion flow and WD model of magnetic field. For correct boundary conditions, we found accretion solutions for fixed and variable gamma using MHD equations.


About Speaker: Mr. Kuldeep is a 2nd year student working with Dr. Indranil.



[193] Topic: General Relativistic Study of Radiatively Driven Jets and Presence of Internal Shocks

Speaker: Mukesh Kumar Vyas
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-06-06
Time: 11:30hr
Venue: Auditorium

Abstract: We study a relativistic fluid jet driven by radiation from accretion disc around a non-rotating black hole. We compute the radiative moments with full relativistic transformations including the effect of bending of light in presence of gravity. We show that the jets, under specific cross section deviates from spherical flow, and exhibits multiple sonic points and internal shocks. We obtain multiple shocks and studied their stability properties.


About Speaker: Mr. Mukesh Kr. Vyas is a 3rd year student working with Dr. Indranil.



[190] Topic: Study of magnetic activities on late-type stars

Speaker: Subhajeet Karmakar
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-06-01
Time: 15:30hr
Venue: Auditorium

Abstract: The solar-type stars show rich variety of magnetic activities such as surface inhomogeneities due to presence of dark spots, short and long-term variations in spot-cycles and flares. Using Swift observations, we present an in-depth study of two superflares (F1 and F2) detected on active binary system CC Eridani. The peak X-ray luminosity in 0.3-50.0 keV reached up to 3×10^32 erg/s and 5×10^31 erg/s, which is ∼3500 and ∼600 times more than the quiescent value and larger than any other previously observed flares on CC Eri. Spectral analysis indicates a presence of three temperature corona with first two plasma temperatures remain constant during the flares at ∼3 MK and ∼10 MK. The flare-temperature peaked at 342 MK and 119 MK for F1 and F2, which is ∼4 and ∼2 times more than the minimum value. The abundances peaked at 2.0 and 1.2 solar abundances, which is larger than a factor 11 and 7 than quiescent values. Using hydrodynamic modeling we derive loop-lengths for both flares to be 1.25±0.13×10^10 cm and 1.26±0.20×10^10 cm, respectively. Significant amount of heating is detected during the decay of both the flares. We model the K-alpha emission feature as fluorescence from the hot flare source irradiating the photospheric iron, and estimate the location of the flare at an astrocentic angle of ∼88.2◦. Using the Kepler observations we have analysed an F-type ultra-fast rotator KIC 6791060. We have developed an automated flare search algorithm to detect the flare and to automatically identify the flare start and end time. During the observations, a total of 38 optical flares are detected. Energies of these flares have been found to vary within a range of 1031−34 erg. Preliminary results of surface temperature modeling indicate an existence of two active longitude region on the stellar surface.


About Speaker: Mr Subhajeet Karmakar is a 5th year PhD student working with Dr. Jeewan C Pandey.



[186] Topic: QSOs absorption line(QSOABL)- tool to probe the evolution of Universe

Speaker: Sapna Mishra
Affiliation: ARIES NAINITAL
Date (yyyy-mm-dd): 2016-05-24
Time: 15:30hr
Venue: Auditorium

Abstract: Study of absorption line systems seen in the spectra of distant QSOs, has played a remarkable role in probing the evolution of the Universe. Tremendous amount of research has been done on absorption line systems e.g. Lyman-alpha forest, Lyman-limit and Damped Lyman alpha systems along the line of sight of QSOs which is a unique tool to prob the proto-galaxy at high redshift. Their studies are important in predicting the physical and kinematic properties of intervening galaxies and IGM. With this idea I will discuss the major research and conclusions made in the field of astronomy from the studies of QSOABL. At the end I will relate my research work with the study of the absorption system of these high redshift objects


About Speaker: JRF at ARIES



[184] Topic: Constraining Cosmological Baryonic Density Using Primordial Nucleosynthesis

Speaker: Anurag Mishra
Affiliation: IIST, Trivandrum
Date (yyyy-mm-dd): 2016-05-18
Time: 15:30hr
Venue: ARIES auditorium

Abstract: Cosmological Microwave Background (CMB) observations in past 50 years have provided wealth of information about Cosmological Parameters. Planck CMB observations favour Universe dominated by Dark Energy (69%) and amount of Baryonic matter is about 2%. It turns out that using Primordial abundances of light nuclei some of the Cosmological Parameters can be constrained. Deuterium, that undergoes very less astration, is the best ‘Baryometer’ and is used to constrain cosmological Baryonic Density Parameter. In this talk we will focus on how Primodial Nucleosynthesis can be used as a tool to constrain Baryonic parameter using Quasar absorption line studies. In this context our recent result based on analysis to measure Deuterium abundance, along QSO J1558-0031 observed with HIRES/Keck, will also be presented.


About Speaker: Anurag Mishra has just completed B.Tech. (Physical Sciences) at IIST, Trivandrum through ISAT program.



[181] Topic: Multi-wavelength analysis of short-duration GRBs using 10.4m GTC and other telescopes during 2012-2015

Speaker: Shashi Bhushan Pandey
Affiliation: Sc-D
Date (yyyy-mm-dd): 2016-05-12
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: {We aim to investigate the prompt emission and afterglow properties of short-duration GRBs including GRB 130603B and other events observed during 2012-2015.} {Multi-wavelength prompt emission and afterglow data of total eight short duration gamma-ray bursts were calibrated to study the temporal and spectral properties.} {Earliest ground-based optical photometry, millimeter-wavelength observations and spectroscopy of GRB 130603B and multi-band data of other seven short duration bursts were used to constrain the nature of these energetic explosions.} {For GRB 130603B, the new data including the earliest photometric observations and the published ones broadly follow the ISM afterglow model. Modeling of the host galaxy of this burst using LePHARE model supports that the environment of this burst is undergoing with moderate star formation activity. Our observations support the requirement for rather early and deeper multi-band observations of many of these events to detect the afterglow or to constrain the possible blue emission from associated ``kilonovae'.}


About Speaker: The speaker is at ARIES and work towards energetic transient events. This presentation is to submit a paper to A&A based on the data discussed in the paper.



[180] Topic: Astrophysical shocks in Hydrodynamic and Magnetohydrodynamic regime

Speaker: Kuldeep Singh
Affiliation: ARIES NAINITAL
Date (yyyy-mm-dd): 2016-05-10
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: The starting of the talk comprises the perturbation in the fluid flow and their analysis under linear assumption. Then I will discuss how these perturbations lead to the formation of shocks. Then we will discuss the theoretical aspects of Hydrodynamic and Magnetohydrodynamic shocks in detail. The latter part will consist of their implications in astrophysical context.


About Speaker: JRF



[179] Topic: HI Emission from Low surface Brightness Galaxies

Speaker: Alka Mishra
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-05-06
Time: 15:30hr
Venue: Auditorium

Abstract: We present HI observations of four giant low surface brightness (GLSB) galaxies UGC 1378, UGC 1922, UGC 4422 and UM 163 using the Giant Meterwave Radio Telescope (GMRT) as part of the study of seven GLSB galaxies in HI and radio continuum (Mishra et al. 2015). LSB galaxies are late type spirals, either blue or red in color, with diffuse stellar disk and wide range in morphology. We examine the morphology and the dynamics. HI is detected from all the galaxies and the extent is roughly twice the optical size and found the HI masses of the order of ≥ 109 M⊙. We combine our results with those in literature to further understand these systems. Recent star formation traced by near-ultraviolet emission in the GLSB galaxies in our sample appears to be located in rings around the galaxy centre.


About Speaker: She is a PDF at ARIES and she has applied for the extension.



[175] Topic: Ambipolar Diffusion

Speaker: Ekta Sharma
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-04-12
Time: 15:30hr
Venue: Auditorium

Abstract: Stars are inevitable offsprings of self-gravity of interstellar matter once it becomes comparable to the disruptive forces due to magnetic fields, thermal pressure. In magnetic mediated theory of star formation, the gravitational collpase of clouds is believed to take place through “ambipolar diffusion”. I will discuss the role of Ambipolar Diffusion in star formation and how it can explain the possible time scale of dynamical collapse.


About Speaker: She is a second year PhD student and working with Dr Maheswar Gopinathan.



[173] Topic: Multi-wavelength Studies of Blazars

Speaker: Ms Aditi Agarwal
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-04-08
Time: 15:30hr
Venue: Auditorium

Abstract: Active Galactic Nuclei (AGNs) are extremely powerful objects emitting over a wide range of wavelengths from radio to gamma-rays. An AGN is a complex system consisting of the central super-massive black hole, an accretion disk, dusty torus, and clouds of gas orbiting the black hole, as well as out-flowing matter (which moves away from the central black hole) in the form of collimated relativistic jets. Two major classes of AGNs that have been established are radio-loud and radio-quiet. Flat spectrum radio quasars (FSRQs) and BL Lacerate objects (BL Lacertae) together are coined as blazars, a subset of core dominated radio-loud AGNs, known to be variable at all accessible time scales over entire EM spectra. The spectral energy distribution (SED) of blazars display two well-defined broad spectral components. Blazars are the special laboratories for extreme physics which we would like to explore. The analysis presented in this thesis is aimed to provide a more detailed multi-wavelength understanding of blazars. We have analyzed Optical and Radio observations together with multi-frequency archival data of blazars in order to study flux-colour variability at diverse timescales, possible quasi-periodic oscillations (QPOs), correlated variability, multi-band SEDs, spectral Indices variations and core shift effect. We have developed statistical techniques and the analysis methodology to extract the maximum possible information from an observed blazar light curve. We have carried out quasi-simultaneous and relatively dense temporal observations of four blazars (2 BL Lacertae and 2 FSRQs) during the observing season 2012 − 2016. This is extensive study of these blazars on all timescales. Also, we searched for the colour variations on intraday and short timescales but significant colour variation was observed only on few instances for these targets which can be attributed to the models involving shock propagating down the jets. We searched for possible correlations between colour and magnitude and obtain that all blazars followed the bluer-when-brighter trend which can be explained by the shock-in-jet models. From the intraday LCs, we inferred the variations to be simultaneous in both the filters which was confirmed by Discrete correlation function (DCF) analysis technique. Optical QPOs were found in blazars on intra-day timescales and can be explained by the fluctuations induced by the disk. Assuming the possible weak QPOs in the blazars are real and are associated with the innermost portions of their accretion disk, we estimated their central black hole masses. We presented first detailed investigation of the core shifts with frequency, along with estimation of jet physical parameters in the case of our source sample, observed using single dish observations at five radio frequency bands. We have calculated and explained the parameters that can be derived from the analysis of the radio light curves, including the magnetic field strength and size of the emitting core, based on physical models proposed in earlier literature.


About Speaker: She is Research Scholar and pursing Ph D under supervision of Dr Alok Gupta. This is her Pre PhD submission talk.



[174] Topic: General relativistic description of accretion-ejection mechanism around black holes

Speaker: Rajiv Kumar
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-04-05
Time: 15:30hr
Venue: Auditorium

Abstract: We want to understand the black hole accretion process, outflows and jets, and predict its observational properties. In the study of accretion disc the highly non-linear process involves a transport of angular momentum by turbulent viscosity process and dissipation in the disc by various dissipative process. The disc in a full general relativistic regime is a very hard to study analytically. So here firstly, we have study analytically hydrodynamic disc with using pseudo-Newtonian potential (pNp) around black holes then using full general relativistic (GR) approach. We have compared our analytical accretion solutions with simulation results around black holes. We have developed all type of possible accretion solutions in the disc with using pNp as well as GR. We have mainly focused on shock disc solutions and jets solutions by assuming jet geometry around the black hole. We computed the jet streamline above the equatorial plane using von-Zeipel surfaces and also estimated the mass outflow rates from the disc with using GR approach for non-rotating black holes. In future, we want to do this type of study for rotating black holes.


About Speaker: Mr Rajiv is a PDF at ARIES working with Dr Indranil.



[172] Topic: Hydrodynamics Instabilities in Astrophysical and Atmospheric context

Speaker: Mukesh Kumar Vyas
Affiliation: ARIES, MANORA PEAK, NAINITAL
Date (yyyy-mm-dd): 2016-03-14
Time: 15:45hr
Venue: Auditorium

Abstract: I will sketch the theoretical origin and physical understanding of Rayleigh Taylor and Kelvin Helmholtz instabilities in fluids. This will be followed by their simulations and numerous cases in nature including daily life, earth atmosphere and astrophysical objects (Like Supernovae and crab nebula)


About Speaker: Research Fellow, ARIES



[170] Topic: Observations of Accreting Binaries, Transients and Targets of Opportunity at SAAO

Speaker: Prof. David Buckley
Affiliation: South African Astronomical Observatory
Date (yyyy-mm-dd): 2016-01-29
Time: 11:30hr
Venue: Auditorium

Abstract: I will discuss observations conducted with SALT and other SAAO telescopes of transients and other targets of opportunity, with an emphasis on accreting binaries, namely cataclysmic variables and X-ray binaries. The recently established MASTER-SAAO optical transient detection facility will be described, plus the recent results following from this, particularly relating to new CV discoveries. Future plans for followup observations of transients, detected by various facilities, with SALT and other facilities will also be presented.


About Speaker: Prof. Buckley has been deeply associated with the SALT, the 10-meter class optical telescope in South Africa.



[168] Topic: Optical Hα imaging and spectroscopy of a Wolf-Rayet galaxy Mrk 22

Speaker: Abhishek Paswan
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-01-25
Time: 11:00hr
Venue: Auditorium

Abstract: We present results from narrow-band Hα imaging and optical spectroscopy on a blue compact dwarf (BCD) Wolf-Rayet (WR) galaxy, Mrk 22. The WR emission features namely the blue and red bumps in the optical spectrum are detected. The detection of this WR features indicates that the origin of ionized gas in galaxy could be attributed to existing young massive stars. Hence, the population of hot massive stars in galaxy is also quantified using the WR bumps luminosity. The star formation rate is estimated as 0.04 ± 0.01 solar mass per year. For this region, age of the most recent starburst is found as 5.8 ± 0.7 Myr old using Hα and Hβ equivalent widths. The GMRT HI 21cm - line radio observation reveals that the most likely triggering mechanism responsible for this starburst is interaction or merger with an HI cloud. Furthermore, the physical condition and chemical abundance for various elements are derived. Subsequently, the Oxygen abundance is also estimated from electron temperature of the ionized gas.


About Speaker: Mr. Abhishek Paswan is a research scholar at ARIES.



[165] Topic: Molecular line diagnostic of the radiation-driven implosion mode of triggered star formation in bright rimmed clouds

Speaker: Neha Sharma
Affiliation: ARIES
Date (yyyy-mm-dd): 2016-01-12
Time: 15:30hr
Venue: Auditorium

Abstract: Bright rimmed clouds (BRCs) are the isolated molecular clouds located at the periphery of relatively evolved HII regions, which are found to have many signs of star formation. We present the preliminary results of the pilot study conducted on the two BRCs, BRC 18 and BRC 38 basically to assess the feasibility of mapping observations with HCN (1-0) and N2H+ (1-0) molecular lines using KVN single dish facility. The main aim of this study was to understand the kinematics of the radiation-driven implosion mode of triggered star formation in BRCs.


About Speaker: Ms Neha Sharma is a 5th year Research Scholar working in the field of Astronomy under the supervision of Dr. Maheswar Gopinathan.



[167] Topic: A study on Dynamical aspects of Aerosols over the central Himalayan region

Speaker: Krishna Kumar Shukla
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-12-31
Time: 11:00hr
Venue: Auditorium

Abstract: Atmospheric aerosols are an important entity and are the subject for research in current scenario due to their diverse physical and optical properties. In my thesis work, we have reported the findings on the intriguing aspects of boundary layer and wave induced aerosol dynamics over a high altitude site in central Himalayan region. We have used the Doppler Lidar (DL) and other collocated instruments along with satellite datasets during Ganges valley aerosols experiment (GVAX) 2011-2012 to understand the morphological characteristics of aerosols, long-range trasnport and associated dynamics over the site. Also, we have estimated cloud base height over this site for the first time using Doppler lidar and other collocated instruments and found reasonably good correlation of cloud base heights estimated with different methods and instruments. Now, we would like to extend our work by validating the ground based instruments (Doppler Lidar, Ceilometer etc) with different satellite datasets (space borne Lidar satellite (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)), MODIS, AIRS, CLOUDSAT) over a complex topographic region in the central Himalayan region. During my doctoral work, we have also attempted to understand the short period and long period modulations which could provide a clue of understanding additional heating rates in the atmosphere in episodic events. Now, we will also take long term datasets of different ground based and also global datasets to understand the affect of planetary scale wave modulations over our region. Apart from this, a ST-Radar facility is also coming up at ARIES which will provide high vertical and temporal resolution tropospheric wind measurements which will be used to understand lower tropospheric dynamics over Central Himalayan region.


About Speaker: Mr. Krishna Kumar Shukla has submitted his Ph D thesis under supervision of Dr. Phani Kumar and has applied for the PDF position at ARIES.



[163] Topic: Spatial and Temporal enhancements in Eruptive events

Speaker: Aabha Monga
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-12-17
Time: 15:30hr
Venue: Auditorium

Abstract: I have analyzed the region AR12437 where C2.1 class flare occurred in the South-West area of the Sun observed on October 26, 2015. From the morphological studies, flare eruption shows the Three ribbon structure. This region was least complex with the complexity α. Filament was associated with this flare. Besides the circular ribbon, an inner and an outer (remote) ribbons are often found. I have analyze the event with SDO/AIA and HMI data for the evolutionary studies. This study is also characterized with the X-ray emission to study the energy release processes. I have also used ARIES Hα data and velocity Dopplergrams for the Photospheric study of the region AR11748 for the Intensity- velocity relations.


About Speaker: Ms Aabha Monga is a 4th year Research Scholar working in the field of Solar Physics under the supervision of Dr. Wahab Uddin.



[162] Topic: Study of sparse star clusters and metallicity distribution of the Large Magellanic Cloud.

Speaker: Samyaday Choudhury
Affiliation: IIA Bangalore
Date (yyyy-mm-dd): 2015-12-02
Time: 15:30hr
Venue: Auditorium

Abstract: The Magellanic Clouds (MCs), comprising of the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are two nearby (~50 kpc), interacting galaxies to our Milky Way. In my thesis, I have studied the sparse star clusters and metallicity distribution for one of the component of the MCs, the LMC. The study of sparse star clusters in the LMC is important in order to understand the cluster formation history of the LMC. The study aims to increase our understanding of sparse star clusters in the LMC, using deep Washington photometric data of 45 star clusters obtained from 4 m Blanco Telescope, CTIO. A systematic study was performed to estimate their parameters (radius, reddening, and age) using the main-sequence turn-off, as well as the evolved portion of the color-magnitude diagram (CMD). The basic parameters were estimated for 33 clusters, out of which 23 are identified as single clusters and 10 are found to be members of double clusters. The other 12 cluster candidates have been classified as possible clusters/asterisms. This study emphasises that the LMC has a significant population of clusters, which are similar to the open clusters in our Galaxy. To understand the metallicity distribution and gradient of the LMC, we estimated a metallicity map using the red giant branch (RGB) stars, from the Magellanic Cloud Photometric Survey (MCPS) and Optical Gravitational Lensing Experiment (OGLE III) photometric data. This is a first of its kind map of metallicity up to a radius of 4 - 5 degrees, with good sampling of the bar region. The slope of the RGB is used as an indicator of the average metallicity of a subregion, and it is calibrated to metallicity using spectroscopic data for field and cluster red giants in selected subregions. The bar is found be the most metal-rich region of the LMC, and indicative of an active bar in the past. Both the data sets suggest a shallow radial metallicity gradient up to a radius of 4 kpc. This metallicity gradient of the LMC disk, though shallow resembles the gradient seen in spiral galaxies, and is also similar to that found in our Galaxy.


About Speaker: PhD Student (final year, thesis submitted) Indian Institute of Science (Joint Astronomy Porgram). Indian Institute of Astrophysics.



[160] Topic: PALOMA: A magnetic CV between Polars and Intermediate Polars

Speaker: Arti Joshi
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-10-30
Time: 15:30hr
Venue: Auditorium

Abstract: We present analyses of archival X-ray data obtained from the XMM-Newton satellite and optical (photometric + polarimetric) data obtained from 1.04-m Sampurnanand Telescope at Manora Peak, Nainital and 1.3-m Devasthal Fast Optical Telescope (DFOT) located at the Devasthal, both operated by Aryabhatta Research Institute of Observational Sciences (ARIES) for the candidate magnetic CV Paloma. From the X-ray data, we report two persistent periods at 156 ± 6 min and 130 ± 4 min, which we interpreted as the orbital and spin periods which are strongly indicated in the power spectrum of the time series. These periods are similar to those obtained from the optical data. The averaged X-ray spectral data obtained with EPIC-PN and MOS detectors are well fitted by a two apec component with temperatures of 0.093 +/-0.011 and 12.57 +/- 0.55 keV with an Fe Kα line and an absorbing column density of 6.1 × 10 22 cm -2 . This material partially cover 64 ± 1 % of the X-ray source. We also present the orbital and spin phase-resolved spectroscopy of Paloma in 0.3 − 10.0 keV energy range and found that X-ray spectral parameters show orbital and spin phase dependences. Details of the results are presented and discussed. These results show that Paloma belongs to a class of a few magnetic CVs that have same characteristics of both the polars and intermediate polars.


About Speaker: Ms. Arti Joshi is a fourth year Ph. D. student at ARIES.



[158] Topic: Proposed Spectral Collocation of a Multi-Mode Solar Dynamo

Speaker: Prof. Steven Pearce
Affiliation: Simon Fraser University, British Columbia, Canada
Date (yyyy-mm-dd): 2015-09-30
Time: 15:30hr
Venue: Auditorium

Abstract: This talk will review the current state-of-affairs concerning solar dynamo theory. A recent sensationalized publication by Professor Valentina Zharkova has prompted a concerted effort to produce an accurate spectral collocation MHD simulation in order to demonstrate the feasibility of a mult-mode dynamo process in the convective layer of the sun. As such, we will review of the Grand Minima Problem and provide a brief review of our spectral collocation technique and provide an illustrative geodynamo model calculation recently announced at the Wessex Institute demonstrating the advantages of this method.


About Speaker: Prof. Steven Pearce is faculty in Simon Fraser University, British Columbia, Canada. Now a days he is visiting faculty at Indian Institute of Information Technology (IIIT), Allahabad.



[157] Topic: Study of tropospheric trace gases over the Indian subcontinent

Speaker: Piyush Bhardwaj
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-09-24
Time: 15:30hr
Venue: Auditorium

Abstract: Surface based observations of O3, CO, light NMHCs and BC were made during the international field campaign SusKat-ABC during Dec 2012–June 2013 in the Kathmandu valley and surrounding regions. The diurnal variations at Bode were typical of a polluted urban site with sharp day time build up in O3, and CO having higher levels during morning/evening hours. The early morning CO levels were higher during winter (Jan-Feb, ~ 1500 ppbv) than spring (Mar-May, ~1100 ppbv). However, daytime O3 levels were slightly higher during spring (~62 ppbv) when compared with those during winter (~54 ppbv). High resolution WRF-Chem setup was done over Kathmandu valley (9, 3, 1 km). Large differences in the meteorological parameters were observed with nightime differences being the highest. Differences in temperature and RH were ~1 oC, 10% during daytime and 4-8 oC, 40-60% during night-time respectively. Wind speeds and directions were in good agreement. Model was warm and drier during night time and was unable to capture fog at night. The day and night-time differences in O3 were ~25 and ~50ppb respectively and CO showed even larger day/night differences 100-200 ppb during daytime and 500-1500 ppb at night. These differences improved with some modifications in model but still large differences were observed at Bode. The similar differences in meteorology at a mountain top Nagarkot was much lower (<10%) and model performed well there.


About Speaker: He is a 5th year Research Scholar.



[156] Topic: Time variability and physical properties of AGN.

Speaker: Prashanth Mohan
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2015-09-15
Time: 15:30hr
Venue: ARIES AUDITORIUM

Abstract: Variability in active galactic nuclei (AGN) spans a wide range of timescales from a few 100 s (gamma rays) to a few years (optical and radio). Here, we present recent models and constraints on the AGN jet properties and black hole mass. We first study the effects of radiation pressure and drag which stabilize the outflow with Lorentz factors of 1.1 - 7, used as inputs to a model of jet based variability. Then, we describe the radio core shift effect in blazar 3C 454.3 using the 4.8 GHz - 36.8 GHz long term radio light curves. We infer a magnetic field strength of 0.07 - 1.43 G at 1 pc and 0.03 - 0.17 G at the core. A Fourier periodogram analysis yields power law slopes ranging between -1.6 and -3.5, and gives bend timescales ranging between 0.52 and 0.66 yr. Flares originate from multiple shocks in a region at a distance of a few to tens of parsecs from the central region. We then study the ~ 1.6 yr Kepler light curve of the blazar W2R 1926+42. A bend timescale of 3.1 - 12.6 hours is inferred. Using this and the normalized excess variance, we infer a black hole mass of (1.5 - 5.9) x 10^7 M_sun. We argue that the observed variability and an inferred weak and short duration quasi periodic oscillation could be due to jet based orbital features and others such as shocks and turbulence.


About Speaker: He is PDF at ARIES.



[155] Topic: Study of Aerosol characteristics over central Himalayas

Speaker: Ms Hema Joshi
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-09-11
Time: 15:30hr
Venue: Auditorium

Abstract: Multiyear measurements of aerosols are studied over the central Himalayas in view of the crucial role played by aerosols in climate change, radiation budget, and air quality. The ground based aerosol measurements over the central Himalayan region were utilized to understand aerosol variability and trends at a high altitude site, while the first time absorbing aerosols characterization was made at a low altitude semi urban site in the Indo-Gangetic Plain (IGP) region, adjacent to Himalayan foothills. The ground based examination of aerosols are complemented by space-borne sensors to explain and discuss the surface, columnar, and vertical distribution of aerosols over this region. The roles of meteorological processes such as boundary layer dynamics, convection, regional and long-range transport along with possible sources of aerosols, their seasonality and processes governing the observed concentration or loading are discussed in detail. The aerosol characterization over this region is also discussed in context to other locations. The current state of the science of chemical transport model known as the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem) was examined for absorbing aerosol, BC. Further, it is shown that agricultural crop residue burning in northern India significantly affects the aerosol load in the central Himalayas which has implications for the atmospheric thermodynamics in this region. These investigations carried out here further motivated to identify the source types of these aerosols and their seasonality in detail. The multiyear data is proposed to use to the source apportionment and estimating aerosol impacts.


About Speaker: She has applied for the RA under a ISRO project.



[154] Topic: Investigating supernovae and probing its CSM

Speaker: Mr Subhash Bose
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-09-04
Time: 15:30hr
Venue: Auditorium

Abstract: We characterized a number of core-collapse supernovae events which has been extensively observed in photometric, spectroscopic and polarimetric modes at optical wavelengths. Our primary goal was to understand various mechanisms involved in the explosion and how they govern observable parameters. We utilized the observational data to constrain progenitor properties, explosion parameters and also to probe circumstellar environment to infer their pre-SN evolution which the progenitor might have undergone. We also probe various peculiarities these SNe exhibits in their observed light curves and spectra. In this talk I shall briefly summarize the key aspects which I investigated in my thesis and shall discuss the scope of further work which I propose to do. Expanding photosphere method (EPM) has been demonstrated to be a reliable distance estimator at extragalactic scale. It would be interesting to extend the work to higher redshift SNe, which would require few epoch of observations during the first month of explosion. Apart from astronomical importance of the estimated distances, it can be used to construct Hubble diagram having a sample of sufficiently high-z SNe. Probing the circumstellar interaction is also a key proposed idea of my future work, which may reveals a wealth of information about the history of pre-SN stellar explosion. As in SNe IIn, where profound interaction occurs between ejecta and extended dense shell of material originated from mass loss of massive WR type progenitors during its stellar life. The study of these interactions give information about the environment and progenitor when the mass loss of the shell happened back in time. Additionally I shall also investigate type IIL or fast declining events to answer some of interesting question which arose from my thesis work. The prevalence of CSM interaction in SNe IIL and its connection with unusual flattening of of HI velocity are also to be examined on more of such events.


About Speaker: He has submitted his PhD thesis and has applied for the PDF position at ARIES.



[152] Topic: Study of Galactic Star Forming Regions and related Instrumentation

Speaker: Neha Sharma
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-27
Time: 14:30hr
Venue: Auditorium

Abstract: To obtain the polarization due to the dust grains that are present in the cloud, it is essential to subtract the polarization due to those that are present foreground to the cloud. The polarization vectors of foreground subtracted 186 stars are over-plotted on the WISE 12m image as shown in Fig. 1. The mean values of P% after the subtraction of the fore- ground interstellar polarization is obtained as 1.5 %. The mean value of P is found to be 40 which is considered as the mean direction of the plane of the sky component of magnetic eld in Gal 110-13. Based on far-infrared, HI and CO data of the region, Odenwald et al. (1992) proposed cloud-cloud collision scenario to be the most preferred mechanism responsible for the formation of Gal 110-13. They suggested that the Gal 110-13 was formed as a result of the interaction between two HI clouds moving across the line of sight and having velocity components of 􀀀8 and 􀀀6 km s􀀀1. They also suggested that the southern part compared to the northern part is in an advanced stage which resulted in it being predominantly molecular. According to Odenwald et al. (1992), based on HI observations, collided clouds have traveled across the line of sight in the northeast􀀀southwest direction. But the current magnetic eld geometry is almost perpendicular to the proposed direction of the interaction of the clouds. Also, the simulations show that irrespective of the initial eld con guration, in both parallel and perpendicular cases the eld distribution after the shock interaction was found to be chaotic especially on the large scales (Marinho et al., 2001). However, the observed magnetic eld lines from polarization are found to be uniformly distributed contrary to the results from the simulations. Lee and Chen (2007) have considered either a supernova explosion or ionization fronts from a massive star in the vicinity of Gal 110-13 as alternate mechanism that might have caused its cometary shape.


About Speaker: She is a 3rd year research scholar and pursuing PhD with Dr. Maheswar Gopinathan



[153] Topic: Investigating the Behaviour of Exploding Stars

Speaker: Mridweeka Singh
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-27
Time: 15:30hr
Venue: Auditorium

Abstract: Supernovae are the dominant sources of stellar feedback, which plays an important role in regulating galaxy formation and evolution. They are widely recognized as end stages of stellar evolution. During the previous three observing seasons from October 2014 to June 2015 we observed a number of events covering various subtypes of SNe such as Ia, Ib and IIP starting from nearly 10 days after discovery and lasting upto approximately 200 days. Amongst these we present preliminary light curve and color curves of a type Ib event M12045 in NGC 4080. We compare the absolute magnitudes of M12045 with other Ib SNe. An early time spectrum at +12 days is also presented and shows the prominent He feature typical of Ib SNe.


About Speaker: She is 2nd year Research Scholar and pursuing PhD with Dr. Kuntal Mishra



[148] Topic: A search for the elusive radio-quiet BL Lacs

Speaker: Parveen Kumar
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-26
Time: 15:30hr
Venue: Auditorium

Abstract: The Sloan Digital Sky Survey (SDSS) and Two-Degree Field QSO Redshift Survey (2QZ) have revealed a population of Active Galactic Nuclei (AGNs) with peculiar spectral characteristics. These objects have featureless optical discovery spectra resembling BL Lac objects. However, they are significantly quiet in radio and X-ray bands compared to classical BL Lacs. These objects could therefore belong to the hitherto unrecognized population of radio-quiet BL Lacs or radio- quiet quasars without a Broad Line Region (BLR). How such objects fit into the AGN unification picture is an open question. Polarization and variability are the two main characteristic properties of BL Lac objects. Last year, I was involved in two such project,first one is polarisation and spectroscopy study of radio-quiet BL Lacs. Therefore, we selected a sample of 19 radio quiet BL Lacs, from 2QZ and SDSS to study their polarisation, optical variability and spectroscopy. Polarimetric and spectroscopic observations of these 19 radio quiet BL Lacs were carried out using the 3.6m telescope at European Southern Observatory (ESO La Silla, Chile). Here we found optical polarisation around ∼ 1% for our this sample. We did not find high polarisation (P > 3%), like BL Lacs in our sample of radio quiet BL Lacs objects. Regards spectroscopy, we found weak emission line in few sources. It is may be due to small sample to detect such a rare class of AGN, radio-quiet BL Lacs. To find such a rare class, a good sample is needed. We have a sample of ∼ 40 radio-quiet weak emission line quasars with intranight optical variability (INOV) observations and it would be very interesting if we found BL Lacs like polarisation in these objects. Second is continuation of our search for the elusive radio-quiet blazars, by carrying out a systematic programme to detect intranight optical variability (INOV) in a subset of ‘Weak-Lines- Quasars’ (WLQs) which are designated as ‘high confidence BL Lac candidates’ and are known to be radio-quiet. For 19 such RQWLQs, we present here the INOV observations taken in 40 sessions of durations ≥ 3.5 hours each. The 40 differential light curves (DLCs), thus obtained for the 19 RQWLQs, were subjected to an statistical analysis using the F−test and the deduced INOV char- acteristics of the RQWLQs are compared with those published recently for several prominent AGN classes, also using the F−test. However, since the RQWLQs are generally 1−2 magnitudes fainter, a rigorous comparison has to wait for somewhat more sensitive INOV observations than those pre- sented here. Based on our existing INOV observations, it seems that RQWLQs in our sample show a significantly higher INOV duty cycle than radio-quiet quasars and radio lobe-dominated quasars. Two sessions, when we detected rather strong (blazar-like) INOV for RQWLQs are pointed out and both these RQWLQs are therefore candidates for radio-quiet BL Lacs.


About Speaker: He is a 3rd year Research Scholar and pursuing PhD with Dr. Hum Chand.



[150] Topic: Star Formation Aspect in Different Environments of Star Forming Galaxies

Speaker: Abhishek Paswan
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-26
Time: 16:30hr
Venue: Auditorium

Abstract: We present our annual report on studied works whi h have been arried out during the session 2014-2015. Our work omprises mainly the study of star formation rates (SFRs) in nearby star- forming galaxies at their di erent evolutionary stages su h as galaxies belong to the blue loud (late-type with re ent star formation) and red sequen e (early-type with residual or suppressed star formation). Hen e regarded these points we have studied a sample of Wolf-Rayet galaxies from Brin hmann et al. (2008) atalogue showing re ent star formation events using H narrow- band imaging from 1.3-m Devasthal opti al teles ope. For these galaxies, we also used spe tros opi data from SDSS survey in order to make several orre tions to the observed H ux and to derive more other related physi al parameters from the spe trum of galaxies. In addition, we have also studied a volume-limited sample of blue early-type galaxies taken from S hawinski et al. (2009) atalogue showing residual or suppressed star formation events using 1.4 GHz radio ontinuum data from the VLA FIRST survey along with opti al data from the SDSS survey.


About Speaker: He is a 4th year Research Scholar and pursuing PhD with Dr. Amitesh Omar.



[151] Topic: Co-spatial Photospheric enhancement and H alpha evolution of the X-class flare

Speaker: Aabha Monga
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-26
Time: 14:30hr
Venue: Auditorium

Abstract: My work includes the evolution of the Flare and the active region AR11748 where the X1.2 class are is observed on May 15, 2013 with the magnetic complexity . The active region was spread in the area of 310 km2 in the North-Eastern limb of the Sun. I have analyzed the region and are with different wavelength data sets to nd its evolutionary behavior. Flare shows the two ribbon structure and I also found that stationary brightening propagates along the southern ribbon. On the contrary, I found the emerging material from the same region was the driver of the instability. I did not nd the any lament associated with the are. For the morphological evolution of the active region, I have used SDO data and I have used SDO/HMI magnetograms and the velocity Dopplergrams for the photospheric magnetic parameters. From this study, I conclude that are occurred in the lower corona and the coronal loops moved upward which gives the signature of the magnetic reconnection beneath the uprising loops.


About Speaker: She is 3rd year Research Scholar and pursuing PhD with Dr. Wahab Uddin.



[147] Topic: Multi-wavelength study of Magnetic Cataclysmic Variables (CVs)

Speaker: Arti Joshi
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-24
Time: 16:30hr
Venue: Auditorium

Abstract: We present analyses of archival X-ray data obtained from the XMM-Newton satellite and op- tical (photometric + polarimetric) data obtained from 1.04-m Sampuranand telescope (ST) at Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital and 1.3-m Devasthal Fast Optical Telescope (DFOT) located at the Devasthal, Nainital for the candidate magnetic CV Paloma. From the X-ray data, we report two persistent periods at 156±6 min and 130±4 min, which we interpreted as the orbital and spin period which are strongly indicated in the power spectrum of the time series. We also interpreted Paloma is a key object for magnetic CV evolution with an orbital period right within the period gap. Photometric and Polarimetric observations of ten mag- netic CVs were also carried out in 84 nights from ST and DFOT at ARIES , among all these CVs we present the photometric results of the five candidates 2MASSJ0130+6221, 2MASSJ0345+5335, RXJ0749-0549, RXJ0859+0537 and 1RXSJ1858+4914. Three of the systems 2MASSJ0130+6221, RXJ0749-0549 and RXJ0859+0537 was found to be eclipsing from photometric data and have orbital periods above the CV period gap of 2-3 h.


About Speaker: She is 3rd year Research Scholar and pursuing PhD with Dr. Jeewan C pandey.



[149] Topic: Study of magnetic activities on late-type stars

Speaker: Subhajeet Karmakar
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-24
Time: 15:30hr
Venue: Auditorium

Abstract: The solar-type stars shows rich variety of magnetic activities such as surface inhomogeneities due to presence of dark spots, short and long-term variations in spot-cycles and flares. Using the wealth of ∼24 yr multi-band data, we present an in-depth study of the evolution of starspot distributions, optical-flares, Surface Differential Rotations (SDR) and coronal activities on the surface of young, single, main-sequence, Ultra Fast Rotator (UFR) LO Peg. With V-band data a rotational period of 0.422923 ± 0.000005 d has been established. In our study for the first time we have investigated the long-term periods of LO Peg. Evidence of existence of three periods of ∼2.98 yr, ∼7.44 yr and ∼11.8 yr have been detected. Using the seasonal variations on rotational period we also investigate the SDR pattern. LO Peg shows a solar-like pattern of SDR, that is the rotational period steadily decreases along the activity cycle, jumping back to higher values at the beginning of the next cycle with a cycle of 2.8 yr. During the observations 20 optical flares are detected with a derived flare frequency of ∼1 flare per two days. Energies of these flares have been found to vary within a range of 10^{32−34} erg. Using light curve inversion technique (iPH code) we have constructed temperature inhomogeneity map of the surface of LO Peg. The surface coverage of cool spots is found to be in the range of ∼6-27%. It appears that the high and low latitude spots are interchanging their positions. Using XMM-Newton observation, we investigate properties of a flare from the very active and poorly known stellar system 47 Cas. The luminosity at the peak of the flare was found to be 3.54 × 10^30 erg s^{−1} , which is ∼2 times more than that at quiescent state. The quiescent state corona of 47 Cas was represented by two temperature plasma: 3.7 and 11.0 MK. The time-resolved X-ray spectroscopy of the flare showed the variable nature of the temperature, the emission measure, and the abundance. The maximum temperature during the flare was found to be 72.8 MK. We inferred the length of a flaring loop to be 3.3 × 10^10 cm using a hydrodynamic loop model. Using ∼11 years XMM-Newton data we present flare analysis of a young, main-sequence ultra-fast rotator AB Dor. A total of ∼140 X-ray flares were detected in the entire span of observations. Evidence of two temperature quiescent corona at 3.36 MK and 11.1 MK is seen. The density of each flare is derived at the range of 2-10 X 10^10 cm^{−3} . The flaring loop length is found to vary in the order of 1010 cm.


About Speaker: He is a 4th year Research Scholar and pursuing PhD with Dr. Jeewan C pandey.



[144] Topic: Multi-wavelength studies of Blazars

Speaker: Aditi Agarwal
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-21
Time: 16:30hr
Venue: Auditorium

Abstract: To search for optical variability on a wide range of time scales, we have carried out photometric monitoring of two flat spectrum radi o quasars, 3C 454.3 and 3C 279, plus one BL Lac, S5 0716+714, all of which have been exhib iting remarkably high activity and pronounced variability at all wavelengths. CC D magnitudes in B, V, R and I pass-bands were determined for ∼ 7000 new optical observations from 114 nights made during 2011 – 2014, with an average length of ∼ 4 h each, at seven optical telescopes: four in Bulgaria, one in Greece, and two in India. We measured multiband optical flux and colour variations on diverse timescales. Discrete corr elation functions were com- puted among B, V, R, and I observations, to search for any time delays. We found weak correlations in some cases with no significant time lags. The structure function method was used to estimate any characteristic time-scales of vari ability. We also investigated the spectral energy distribution of the three blazars using B, V, R, I, J and K pass-band data. We found that the sources almost always follows a bluer -when-brighter trend. We discuss possible physical causes of the observed spectral v ariability. Project 2 : We monitored BL Lacertae for 13 nights in optical B, V, R, and I bands during October and November 2014 including quasi-simultan eous observations in V and R bands using two optical telescopes in India. We have studie d multi-band optical flux variations, colour variation and spectral changes in this b lazar. Source was found to be active during the whole monitoring period and showed signifi cant intraday variability on 3 nights in V and R filters while displayed hints of variabil ity on 6 other dates in R passband and on 2 nights in V filter. From the colour-magnitud e analysis of the source we found that the spectra of the target gets flatter as it becom es brighter on intra-night timescale. Using discrete correlation technique, we found that intraday light curves in both V and R filters are almost consistent and well correlated with each other. We also generated spectral energy distribution (SED) of the target using the B, V, R, and I data sets for all 13 nights which could help us investigate the phy sical process responsible for the observed variations in BL Lacertae objects. We also disc uss possible physical causes of the observed spectral variability. Project 3 (ongoing) : In this project, we study variability of ∼ 15 blazars on all three timescales using Optical/NIR photometric observati ons. We found significant flux variations in most of them. We have measured the multiband op tical flux and colour variations in these blazars on intra-day and short-term tim escales. We also plan to investigate the spectral slope variability and possible co rrelations between colour and magnitude to differentiate between FSRQs and BL Lacertae obj ects. We also plan to do cross-correlation analysis to search for time delays.


About Speaker: She is 3rd year research scholar and working with Dr Alok Gupta



[145] Topic: Studies of Nearby Star-Forming Galaxies

Speaker: Sumit Jaiswal
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-21
Time: 15:30hr
Venue: Auditorium

Abstract: We have performed two surveys namely HI survey and Ha survey of a sample of WR galaxies. The main aims of this study are to see the optical and radio morphology of these galaxies and role of environment interactions in triggering the starburst in them and to find the star formation rate in the sample galaxies using Ha data and compare it with other SFR indicators. 3 We present the gray-scale Ha and R band images of few galaxies of our sample in figure 1. All the images have their north up and east left. A linear scale-length in kpc is shown at the bottom of each image. The R-band images traces the old stellar population in the galaxy and therefore it can provide the features of galaxy interactions. On the other hand, the Ha images traces the ionized gas (HII regions) and therefore it provides the distribution of star forming regions in the host galaxy with respect to the environmental effects. The clear interaction features can be seen in most of the galaxies in the sample. This result can be used to speculate that the galaxy-galaxy tidal interaction could be the main cause of massive star formation in galaxies. We also present the HI column density maps of few galaxies of our sample in figure 2. The HI column density contours are overlaid on the gray-scale DSS image. These images show a clear indication of tidal interaction in these galaxies through various asymmetries.


About Speaker: Mr Sumit Jaiswal is pursuing PhD with Dr. A Omar.



[146] Topic: A Study on Dynamical Aspects of Aerosols over the Central Himalayas

Speaker: Krishna K Shukla
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-21
Time: 14:30hr
Venue: Auditorium

Abstract: During the Indo-US collaborative Ganges Valley Aerosol Experiment (GVAX), a Doppler Lidar was operated continuously from June 2011 - March 2012 at a high altitude site Manora Peak (29.4o N; 79.2o E; 1958 m, amsl) in the Himalayan foothills. The Doppler Lidar provides height-resolved measurements of vertical velocity and attenuated backscatter over the site. Doppler Lidar and Multi Filter Rotating Shadow band Radiometer (MFRSR) observations are utilized to show wave like signatures in AOD during daytime atmospheric boundary layer (ABL) evolution over the Himalayan region. Fourier analysis depicted 60-80 min periods dominant during afternoon hours, implying that the observed modulations could be plausible reason for the AOD forenoon-afternoon asymmetry which was previously reported. Inclusion of wave amplitude in diurnal variation of aerosol radiative forcing estimates showed ~40% additional warming in the atmosphere relative to mean AOD. We also investigate diurnal and seasonal variation of vertical velocity and attenuated backscatter below 1 km, AGL during the post-monsoon (September-November), winter (December-February) and pre-monsoon (March) seasons. The vertical velocities exhibit a strong diurnal pattern throughout the observational period depicting upslope flows during daytime and down slope flows during nighttime. The magnitude of the vertical velocity varies between 0.1-0.4 m.s-1 in all seasons. The vertical velocity variance ranges from 0.2-1.5 m2s-2 and was found to be higher during daytime due to strong convection followed by a decrease during nighttime due to cooling at the surface. The magnitude of attenuated backscatter varies between -6.5 and -5 m-1sr-1 (represents log10 scale) in all seasons. We also investigated the impact of variable weather conditions on vertical velocity and the results are discussed in the light of the current understanding of the boundary layer dynamics over the observational site.


About Speaker: Mr Krishna K Shukla is pursuing Ph D with Dr. D V Phani Kumar.



[142] Topic: Innermost structure of quasars using optical interferometry and reverberation mapping

Speaker: Suvendu Rakshit
Affiliation: OCA, Nice, France
Date (yyyy-mm-dd): 2015-08-20
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: The broad line region (BLR) of Active Galactic Nuclei (AGN) contains the high velocity gas clouds transporting material from the dust torus to the accretion disk around the central super massive black hole (SMBH). Unveiling BLR structure is critical to understand the accretion mechanism driving the SMBH evolution and shaping the AGN inflows, outflows and jets. Reverberation Mapping (RM) constrains the BLR geometry, kinematic, mass and equivalent linear size with parameter degeneracies and fudge factors depending from the source geometry. Optical Interferometry (OI) yields independent constrains on BLR structure, mass and equivalent angular size. We developed a 3D geometrical model of BLRs to estimate both RM and OI measures and to show that the combination of these two techniques will very substantially reduce the uncertainty of mass estimates and yield direct distance measurement from quasar parallax. We used this model and a Monte Carlo Markov Chain Bayesian parameter fit of simulated data to show that quasar parallax can measure distances with accuracy better than 16%. We used it on actual data to interpret and explain our first OI observations of the BLR of the bright quasar 3C273 found to have a BLR of about 1750+/-35 light days (ld) much larger than predicted by RM (450+/-120 ld) and larger than the inner rim of the dust torus of about 800+/-270 ld, yielding a SMBH mass of (5+/-1) 10^8 solar masses. Our model and SNR computations show that the VLTI incoming instruments can observe about 60 BLRs covering more than 4 decades of luminosity, enough to try a grand unification of BLRs models and a calibration of RM making QSOs major cosmological probes.


About Speaker: Ph.D from OCA, Nice, France



[143] Topic: Radiatively driven relativistic jets with variable adiabatic index equation of state

Speaker: Mukesh Kumar Vyas
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-08-18
Time: 14:30hr
Venue: Auditorium

Abstract: We study a relativistic fluid jet driven by radiation from accretion disc around a non-rotating black hole. We compute the radiative moments with full special relativistic transformations. We show that the terminal speed of jets increases with the mass accretion rates, synchrotron emission of the accretion disc and reduction of proton fraction of the flow composition. To obtain relativistic terminal velocities of jets, both thermal and radiative driv- ing are important. We show for very high accretion rates and pair dominated flow, jets around super massive black holes are truly ultra-relativistic, while for jets around stellar mass black holes, terminal Lorentz factor of about 10 is achievable.


About Speaker: This is a review talk by Mr Mukesh, who has completed 2nd year.



[137] Topic: On the nature of extragalactic magnetic fields from Faraday rotation measure

Speaker: Ms Vidushi
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-07-24
Time: 10:30hr
Venue: Auditorium

Abstract: We have investigated the dependance of the residual rotation measure (RRM) on the intervening Mg ii absorber at cosmic distances, by using a large sample of 340 quasars with 518 Mg ii absorbers and 565 quasars without Mg ii absorbers from SDSS and most updated quasar catalog for RM around 21cm wavelength. After discounting the contribution of foreground galactic rotation measure (GRM) of milky way, the residual rotation measure (RRM) of these quasars is used to calculate the excess extragalactic contribution in the standard deviation of the distribution of observed RRM. The excess standard deviation of the sample with intervening Mg ii absorber of about 47.53 ± 0.52 rad m−2 is found in comparison of the sample without Mg ii absorber. Our results suggest that intervening absorbers could contribute in enhancement of RRM at around 21cm wavelength, with a sample which is about twice the largest sample used in literature till now. We have also obtained the evolution of RRM with redshift, which gets saturated at higher z  3 with no Mg ii absorber. It supports the conclusion that magnetic field strength traced by RRM for high redshift galaxies is atleast comparable to the current epoch. The evolution of RRM with redshift also shows that dispersion in RRM is higher for the sample with Mg ii absorber as compare to the sightlines without Mg ii absorber.


About Speaker: She is a first year student at ARIES. This presentation is based on her project work as a part of PhD Course Work.



[134] Topic: Physical state of 21-cm absorber at z_abs ~ 0.3 towards a radio-loud quasar J1443+0214

Speaker: Ms. Avni Parmar
Affiliation: Pune University
Date (yyyy-mm-dd): 2015-07-20
Time: 11:30hr
Venue: ARIES Auditorium

Abstract: Understanding the physical state of the interstellar medium of protogalaxy at high redshift plays a key role in our understanding of galaxy formation. Although it is not possible to directly observe the highly redshifted galaxies, but their signature as absorption line in the background quasar spectrum allow us to study them in both optical and radio regions. The 21-cm line, caused due to the hyperfine splitting in Hydrogen atom, is the signature of cool gas present in the interstellar medium (ISM) of this highly redshifted galaxy. In this regard we study the quasar-galaxy pair (QGP) J1443+0214 with z_qso =1.82, z_abs = 0.3714, by searching for the 21-cm HI absorption at the redshift of foreground galaxy. We use the GMRT archival spectral data centered around 1041.68 MHz with 4.17 MHz bandwidth and process it using Astronomical Image Processing System (AIPS) to obtain HI 21-cm absorption line. We find a very prominent HI absorption at the redshift of foreground galaxy (z_abs = 0.3714),thus concluding that a cool gas phase of ISM is present in this galaxy, estimate the optical depth and spin temperature of HI.


About Speaker: Ms. Avni Parmar a M.Sc final year student of Pune University is Indian Academy Summer Fellow at ARIES.



[135] Topic: SENSITIVITY OF 3.6m DEVASTHAL OPTICAL TELESCOPE

Speaker: Anusree Devanand
Affiliation: Amrita Vishwa Vidyapeetham, Kerala
Date (yyyy-mm-dd): 2015-07-20
Time: 12:30hr
Venue: auditorium

Abstract: The 3.6m optical telescope, currently the largest optical telescope in India is being built at Devasthal with an aim to develop an observational facility with spectral and seeing limited imaging capabilities at visible and near infrared bands. Electromagnetic radiation received on Earth are the major carriers of cosmological information. The ability of a telescope to collect the least possible signal describes its sensitivity. The aim of the project was to characterize the photometric and spectroscopic sensitivity of this telescope. A measure of sensitivity is given by the signal to noise ratio of the telescope. The signal to noise ratio for imaging as well as spectroscopy at various zenith angles and observing conditions has been calculated using MATLAB. In imaging, a signal-to-noise ratio of 3.9 has been obtained for a 25 mag point source in V band, measured at zenith for an exposure time of 30 minutes, using a 4KX4K CCD camera with a pixel size of 15 microns,three days from New Moon. And, in spectroscopy, a signal to noise ratio of 7.5 has been obtained for a 20 mag point source at 0.5 µm, measured at zenith for an exposure time of 10 minutes.


About Speaker: Ms Anusree Devanand is M.Sc. (Physics) 1st year student at Amrita Vishwa Vidyapeetham, Kerala. Ms. Anusree did project work for 2 months at ARIES under Summer Research fellowship program-2015 of Indian academy of Sciences.



[136] Topic: IMAGE QUALITY OF 3.6 m OPTICAL TELESCOPE

Speaker: Anisha
Affiliation: Panjab University, Chandigarh
Date (yyyy-mm-dd): 2015-07-20
Time: 12:00hr
Venue: auditorium

Abstract: The 3.6m Devasthal optical telescope is being installed at Devasthal, Nainital, and it will provide seeing limited observational capabilities at visible and near infrared bands. The image quality of any optical telescope is very crucial to determine accurate physical properties of celestial objects and it can go bad due to variety of reasons such as poor alignment of optics and the environment of telescope.The aim of the project deals with the detection of wavefront distortion induced by misalignment of optics and other imperfections in telescope using Shack Hartmann wavefront sensor. Using modal wavefront reconstruction approach, the distorted wavefront has been reconstructed for 3.6m telescope in terms of Zernike modes and a value of RMS wavefront error of 184nm has been obtained. PSF and MTF of the image are also extracted using these Zernike coefficients. The values obtained are consistent with the image quality specification of the telescope.


About Speaker: Ms Anisha is M.Sc. (Physics) 1st year student at Panjab University, Chandigarh. Ms. Anisha did project work for 2 months at ARIES under Summer Research fellowship program-2015 of Indian academy of Sciences.



[133] Topic: Wavelength Dependence of diffuse-to-global and diffuse-to-direct spectral irradiance over Gangetic Himalayas region

Speaker: Ms. Kanika Pandey
Affiliation: Banasthali University, Rajasthan
Date (yyyy-mm-dd): 2015-07-03
Time: 15:30hr
Venue: Auditorium

Abstract: Continuous measurements of solar spectral radiation using the Multi-filter Rotating Shadow Band Radiometer (MFRSR) were performed at Nainital a high altitude location in the central Gangetic Himalayan region. The present work utilizes two clear-sky days of continuous observations from local sunrise to local sunset, in order to investigate the daily variation of the solar radiation components (diffuse, global and direct-beam) as well as their ratios (diffuse-to-global: DGR; and diffuse-to-direct beam, DDR).


About Speaker: She is MSc Final Year Student, working as a summer training program.



[132] Topic: Instrumentation: CCD and telescope

Speaker: Anjali Lohani
Affiliation: Amity University, Noida
Date (yyyy-mm-dd): 2015-06-26
Time: 12:15hr
Venue: Auditorium

Abstract: The aim of this project is to gain a first hand knowledge of instruments such as CCD and telescope being used in current astronomy. In this project, I have learnt the basic properties of telescope along with a hands on practice with CCD data.


About Speaker: The Speaker is currently enrolled in MSc (1st year) of Amity University, Noida. She is a summer project student here under Dr. Biman J. Medhi.



[130] Topic: Characterization of Atmospheric Surface Layer Parameters during Lightning Conditions

Speaker: Arun Kumar Dwivedi
Affiliation: BIT MESRA, Ranchi
Date (yyyy-mm-dd): 2015-06-17
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: Lightning is the most beautiful as well as dangerous phenomenon appearing in nature. As this is a natural event, it cannot be stopped but some attempts are necessary which may enable us to minimize its disastrous effects. The observational site of this study is BIT Mesra, Ranchi, Jharkhand which lies in the eastern part of India. In my Ph.D. thesis, the behaviours of Atmospheric Surface Layer (ASL) parameters during lightning conditions have been observed. Flux analysis and spectral analysis of these parameters have done during lightning conditions. Based on this, an attempt has been made to develop a model to forecast the lightning occurrence during pre- monsoon season over this region. Artificial Neural Network (ANN) is used to forecast lightning. The results showed that the ANN can be used as an efficient tool for lightning forecasting over this region during pre-monsoon season. Apart from ASL parameters, vertical structure of lower atmosphere is also evaluated using radiosonde data on lightning days and a comparison has been made with the observations during clear days.


About Speaker: Mr. Arun Dwivedi has applied for the PDF position at ARIES.



[129] Topic: Magnetic field geometry of an unusual cometary cloud G110-13

Speaker: Neha Sharma
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-05-26
Time: 15:30hr
Venue: Auditorium

Abstract: Gal110-13 is an isolated, unusually elongated comet-shape cloud, which is considered as an example of star forming region resulting from cloud-cloud collision. We carried out optical polarimetry of G110-13 to understand the importance of magnetic field in the formation and subsequent star formation of G110-13. We compare our results with those from various simulations for cloud-cloud collision and ionization induced cloud evolution and discuss the most preferred mechanism with respect to the magnetic field geometry.


About Speaker: Ms. Neha Sharma is a SRF at ARIES



[125] Topic: Photospheric, chromospheric and coronal activities in late type active stars

Speaker: Manoj Kumar Patel
Affiliation: D.D.U. Gorakhpur University
Date (yyyy-mm-dd): 2015-04-29
Time: 15:30hr
Venue: Auditorium

Abstract: I present analyses of optical photometric, spectroscopic and X-ray observations of binary, V1147 Tau and polarimetric observations of other 43 BY Dra type active stars. The continuous photometric monitoring of active stars will leads to study short term as well as long term variations. The long term photometry and analysis of the light curves help to study the different level of activity, the nature of light variability and possible periodicity. The optical spectroscopy revealed that H alpha is present in emission of V1147 Tau, indicating a high levl of chromospheric activity. The polarization values of 43 stars in B, V, R, and I bands decrease towards longer wavelengths, which indicates the possibility of sources of linear polarization as magnetic intensification arise due to stellar spots and as scattering arise due to the thin circumstellar material. The x-ray light curve was found to be rotationally modulated and was anticorrelated with optical light curves observed at quasi-simultaneous epochs. At the end of the talk, I will discuss the research plan of other type active stars during the PDF


About Speaker: Dr. Manoj Kumar Patel has obtained his PhD thesis awarded from D. D. U. Gorakhpur University. He has applied for postdoc position in ARIES.



[126] Topic: Determination of H_0 through monitoring of gravitationally lensed quasars

Speaker: S. Rathna Kumar
Affiliation: Indian Institute of Astrophysics
Date (yyyy-mm-dd): 2015-04-24
Time: 15:30hr
Venue: Auditorium

Abstract: The Hubble constant at the present epoch (H_0) is an important cosmological parameter on which all extragalactic distances depend. Multiple approaches need to be pursued to constrain its value in order to be able to identify and eliminate unknown systematic errors present in any one approach. Strong gravitational lensing offers one method to constrain H_0 free from calibrations associated with standard candles. It is based on (i) measuring the time delay(s) between the multiple images of a cosmologically distant variable source which is strongly lensed by a galaxy or galaxy cluster that lies in close proximity to its line-of-sight and (ii) modelling the mass distribution of the deflector. We have carried out photometric monitoring of a sample of six gravitationally lensed quasars using the 2-m Himalayan Chandra Telescope (HCT) as part of the COSmological MOnitoring of GRAvItational Lenses (COSMOGRAIL) campaign to measure time delays of most known lensed quasars in both hemispheres using a network of medium-size telescopes. I will discuss in detail our results of this campaign, using a newly devised "difference-smoothing" technique to measure time delay and pixellated modelling of the mass distribution of the deflector to constrain the H_0 value. Further, I will also highlight the usefulness of our time delay measurement technique to other AGN monitoring programs, such as reverberation mapping, often used to infer the kinematics of central regions of AGN using 1-2m class telescopes.


About Speaker: Rathna Kumar has applied for a postdoc position in ARIES.



[123] Topic: Search for Pulsational Variability in Chemically Peculiar Stars

Speaker: Sowgata Chowdhury
Affiliation: Tezpur Univerity (pass out)
Date (yyyy-mm-dd): 2015-04-22
Time: 15:30hr
Venue: New Auditorium

Abstract: The Nainital-Cape survey is a dedicated ongoing survey programme to search and study the pulsational variability in chemically peculiar (CP) stars to understand their internal structure and evolution. The main aim of this survey is to find new pulsating Ap and Am stars in Northern & Southern hemisphere and set-up a platform to perform their asteroseismic study. The survey was conducted using high-speed photometry. The candidate stars were selected on the basis of Str"omgren photometric indices similar to those of known pulsating CP stars. More than 300 candidate pulsating CP stars were observed for the Nainital-Cape survey, making it one of the longest survey ever in terms of time span and sample size. Here, we announce the discovery of Delta Scuti type pulsations in Am star HD73045. Apart from this positive detection, we present the light curves, frequency spectra and the various astrophysical parameters of the 108 additional CP stars observed since the last reporting. We have also tabulated an up-to-date list of known roAp stars along with their basic physical parameters. We investigated the scintillation noise level by comparing the combined frequency spectra of the sample stars observed from ARIES and Sutherland around the same time period. Our analysis shows that the stability of sky at Sutherland is better than ARIES, hence remains one of the best site for detection of milli-magnitude (mmag) order light variations.


About Speaker: Sowgata is a VSP student working under Dr. Santosh Joshi at ARIES since last six months.



[124] Topic: Photospheric, chromospheric and coronal activities in late type active stars

Speaker: Manoj Kumar Patel
Affiliation: D.D.U. Gorakhpur University
Date (yyyy-mm-dd): 2015-04-19
Time: 15:30hr
Venue: Auditorium

Abstract: I present analyses of optical photometric, spectroscopic and X-ray observations of binary, V1147 Tau and polarimetric observations of other 43 BY Dra type active stars. The continuous photometric monitoring of active stars will leads to study short term as well as long term variations. The long term photometry and analysis of the light curves help to study the different level of activity, the nature of light variability and possible periodicity. The optical spectroscopy revealed that H alpha is present in emission of V1147 Tau, indicating a high levl of chromospheric activity. The polarization values of 43 stars in B, V, R, and I bands decrease towards longer wavelengths, which indicates the possibility of sources of linear polarization as magnetic intensification arise due to stellar spots and as scattering arise due to the thin circumstellar material. The x-ray light curve was found to be rotationally modulated and was anticorrelated with optical light curves observed at quasi-simultaneous epochs. At the end of the talk, I will discuss the research plan of other type active stars during the PDF


About Speaker: Mr. Manoj Kumar Patel has recently submitted his thesis in D. D. U Gorakhpur University for PhD degree.



[122] Topic: Stellar Variability and Rotational Activities in the Kepler field.

Speaker: Sowgata Chowdhury
Affiliation: Tezpur University (passout student)
Date (yyyy-mm-dd): 2015-04-17
Time: 15:30hr
Venue: New Auditorium

Abstract: We present the results of time-series photometric analysis of about 15000 stars observed by the Kepler space mission. We measured star-spot rotation periods of 2275 active stars as a function of spectral type and also discuss the distribution of their amplitudes. We examined the period-color relationship for all the Kepler field rotational variables and interestingly found that the same relationship holds true for both early-F and A type stars. This result is not consistent with the very foundation of the PtM relationship. Through visual inspection of the periodograms and the light curves, we identified 16 stars that have previously been mentioned in the literature as red giants with solar-like oscillations. In addition, we found 72 new candidate solar-like oscillators not previously mentioned in the literature. The basic physical parameters such as masses, radii and luminosities of these solar-like oscillators were also derived using asteroseismic relations. We have characterized several non-radial pulsating variables such as delta Scuti, gamma Doradus and hybrid stars and the relationship between two newly constructed observables, Energy and Efficiency have also been studied for the large sample of non-radial pulsators. Our results also support the idea that the present observational instability strip should be extended to accommodate the newly discovered pulsators.


About Speaker: Sowgata Chowdhury was a project student in ARIES from August-2015.



[120] Topic: Analytical and numerical simulation of shock tube problem

Speaker: Sananda Raychaudhuri
Affiliation: Bose Institute
Date (yyyy-mm-dd): 2015-04-16
Time: 15:30hr
Venue: New Auditorium

Abstract: Numerical simulation has become the essential tool for theoretical astrophysicist to under stand various astrophysical system. In this one month project we have regenerated all the necessary solutions to understand the state of the art, high-resolution shock capturing, upwind simulation codes.


About Speaker: Sananda Raychauduri is a course work student in Bose Institute. She is interested to pursue PhD in theoretical astrophysics, and has spent about a month in ARIES as VSPA.



[121] Topic: SN 2013ej - A TYPE IIL SUPERNOVA WITH WEAK SIGNS OF INTERACTION

Speaker: Subhash Bose
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-04-16
Time: 15:30hr
Venue: Auditorium

Abstract: We present optical photometric and spectroscopic observations of supernova 2013ej. It is one of the brightest type II supernovae exploded in a nearby (~ 10 Mpc) galaxy NGC 628. The light curve characteristics are similar to type II SNe, but with a relatively shorter (~85 day) and steeper (~1.7 mag (100 d)^-1 in V) plateau phase. The SN shows a large drop of 2.4 mag in V band brightness during plateau to nebular transition. The absolute ultraviolet (UV) light curves are identical to SN 2012aw, showing a similar UV plateau trend extending up to 85 days. The radioactive 56Ni mass estimated from the tail luminosity is 0.02 M_sun which is significantly lower than typical type IIP SNe. The characteristics of spectral features and evolution of line velocities indicate that SN 2013ej is a type II event. However, light curve characteristics and some spectroscopic features provide strong support in classifying it as a type IIL event. A detailed SYNOW modelling of spectra indicates the presence of some high velocity components in H_alpha and H_beta profiles, implying possible ejecta-CSM interaction. The nebular phase spectrum shows an unusual notch in the H_alpha emission which may indicate bipolar distribution of 56Ni. Modelling of the bolometric light curve yields a progenitor mass of ~14 M_sun and a radius of ~450 R_sun, with a total explosion energy of ~2.3x10^{51} erg.


About Speaker: SRF at ARIES



[118] Topic: Simulation of CO2 transport by a regional model and comparison with observed data

Speaker: Srabanti Ballav
Affiliation: Jadavpur University
Date (yyyy-mm-dd): 2015-04-10
Time: 15:30hr
Venue: New Auditorium

Abstract: The quantification of source-sink distribution of atmospheric CO2 in a finer resolution can become uncertain due to the CO2 transport model-observation data mismatches. In case of the coarse resolution global model, the mismatch occurs mainly due to unresolved sub-grid scale processes, improper representation of the heterogeneity of surface fluxes and model transport behaviour around the measurement site. So far, the high resolution forward transport model simulations of CO2 at hourly to synoptic timescales have attracted considerable interest. Therefore, we have simulated CO2 concentrations as non- reactive trace gas over the Far East Asian region using the regional model WRF-CO2 developed at Jadavpur University, India and RIGC/JAMSTEC, Japan having realistic meteorology as an integral part of the system and has successfully relaxed the limitation in model horizontal resolution. Such a modeling system also accounts for the heterogeneity in the surface fluxes. Using the WRF-CO2 model we have (i) investigated spatio-temporal scale variation of CO2 concentration with observed data, and carried out model inter-comparison with available data from TransCom3 models, (ii) carried out case studies to evaluate performance of the model for synoptic variation of CO2 concentration and meteorology, (iii) evaluated model performance for simulating the vertical profile of CO2 in a tall tower. Results of our study show significant improvement of CO2 transport simulation for the regional models due to increment of horizontal resolution in finer scale. Higher resolution a priori fossil flux produces better concentration than the coarser resolution flux. Temporal variabilities of CO2 at different observation stations are well captured by the model. Particular case studies of CO2 transport during extreme weather conditions have also revealed that the model performs well. Overall, the WRF-CO2 model is found to perform better than global models in terms of CO2 transport. However, the WRF-CO2 model needs to be further evaluated over different regions of the world. Hence, the present work can be extended using recent observational data acquired by the AIRES, Nainital and aircraft measurement of vertical profile over New Delhi by the Japan Airlines CONTRAIL programme with collaboration from JAMSTEC, and other existing ground based and tall tower data in the South Asia region. Although (Kumar and Naja et al. 2012, GMD) have evaluated WRF-Chem for several other chemical species (CO, O3 and NOx), no high resolution chemistry modeling of CO2 transport has been attempted for the south Asia region. Therefore, this project of the WRF-CO2 modelling for the Himalayan region along with central Indian region would be a first time application of a very high resolution CO2 modelling over India. Furthermore, the current work should be extended to understand temporal variations of long-lived CO2 in our geographical locations. The propose project is envisaged to provide the first time high-resolution CO2 dynamic studies over South Asia. Concentration and flux values of CO2 that will be obtained from the model simulation


About Speaker: Srabanti did her doctoral research under the guidance of Prof. Utpal Dey in Jadavpur University. She is post-doctoral applicant in ARIES.



[116] Topic: Importance of Magnetic Fields in Spontaneous and Triggered Star Forming Regions

Speaker: Archana Soam
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-03-31
Time: 15:30hr
Venue: New Auditorium

Abstract: In my thesis work, I have tried to understand the relative importance of the mag- netic fields in the regions such as starless/prestellar cores, cores with low-mass and sub-stellar mass objects, and the triggered star forming regions. To arrive at a statisti- cally significant conclusion of this study, I want to increase the sample of these regions. A detailed study of magnetic field maps towards cometary globules (CGs) L331 and L323 in the vicinity of L328 is planned. We have already studied the magnetic fields in L328. The above mentioned two objects L331 and L323 are similar to L328. So we need to observe them to understand the magnetic field morphology in the entire region. I also want to investigate the magnetic field variation in the filamentary clouds which is quite a new and interesting project. This will give us an insight into the understanding of the role of magnetic fields in the the cores forming along the filamentary molecular cloud structures. In addition, I would complete the project started to understand the characteristics of the photoionised gas from the two nebulae Sim 129 and Sim 130 in open cluster NGC 1893. The radio observations in 610 and 1300 MHz frequencies have already been conducted using GMRT. This study will help us in understanding the photoionsed flow from the surface of the bright-rimmed cloud (BRCs) in the vicinity of the high mass stars. NGC 1893 is a interesting region containing five O type stars present in the neighborhood of two above mentioned nebulae. The preliminary results obtained by us suggest that the ionized gas is flowing along the magnetic field lines. These results are obtained based onto the 610 MHz observations. More elaborated and detailed results are expected from the 1300 MHz observations.


About Speaker: Archana Soam is a 6th year student in ARIES, who have submitted her thesis recently. She has applied for Post Doc in ARIES.



[115] Topic: General relativistic description of accretion-ejection mechanism around Compact objects

Speaker: Rajiv Kumar
Affiliation: ARIES
Date (yyyy-mm-dd): 2015-03-24
Time: 15:30hr
Venue: New Auditorium

Abstract: We want to understand the black hole accretion process, outflows and jets, and predict its observational properties. In the study of accretion disc the highly non-linear process involves a transport of angular momentum by turbulent viscosity process and dissipation in the disc by various dissipative process. The disc in a full general relativistic regime is a very hard to study analytically. So here firstly, we have study analytically hydrodynamic disc with using pseudo-Newtonian geometry around compact objects then using full general relativistic approach. Our accretion solutions are stationary, axisymmetric without or with turbulent viscosity in the disc around non-rotating black holes. We have developed all type of possible accretion solutions in a self-consistent manner for non-dissipative or dissipative process in the disc. We have mainly focused on shock disc solutions and jets solutions by assuming jets flow geometry around BH with their corresponding disc luminosities. From this study We want to relate the four features of a black hole observations, which are the disc luminosity, Quasi-periodic Oscillations (QPOs), spectral states of the disc and emitted jets from the disc and try to connect all these observed features each other with shocked accretion disc around black holes.


About Speaker: Rajiv is a 6th year student of ARIES who have recently submitted his thesis, and has applied for post-doctoral fellowship in ARIES.



[114] Topic: Radio Studies of the Nearby Disk Galaxies

Speaker: Dr. Alka Mishra
Affiliation: DDU, GU, Gorakhpur (UP)
Date (yyyy-mm-dd): 2015-02-27
Time: 15:30hr
Venue: ARIES Auditoriuum

Abstract: Galaxies reside in different environments ranging from isolated field galaxies to dense group/cluster medium. Properties of galaxies are influenced by their surroundings. We present a multifrequency radio continuum study of seven giant low surface brightness (LSB) galaxies and HI study of four spiral galaxies residing in a group using the Giant Metrewave Radio Telescope. Our sample consists of giant LSB galaxies that show signatures of nuclear activity in their optical spectra. All the galaxies are HI rich. We compare the radio images with the near-ultraviolet (NUV) images from GALEX and near-infrared (NIR) images from 2MASS. The galaxies present a divers ity of relative NUV, NIR and radio emission, supporting anepis odic star formation scenario. Our multiwavlength study of this sample suggests that the environment plays an important role in the evolution of these galaxies.


About Speaker: Dr. Mishra has completed here Ph D from Gorakpur University.She is PDF candidate at ARIES.



[111] Topic: First optical and near infrared polarimetry of a molecular cloud forming a proto-brown dwarf candidate

Speaker: Archana Soam
Affiliation: ARIES
Date (yyyy-mm-dd): 2014-12-30
Time: 15:30hr
Venue: Auditorium

Abstract: LDN 328 is cited as an example of a fairly isolated clump contracting to form multiple sub-cores possibly through gravitational fragmentation. In one of these sub-cores, a proto-brown dwarf (L328-IRS) candidate is in the process of formation through the self gravitating contraction, similar to the formation scenario of a low mass normal star. We present results of our optical and near infrared polarisation observations of regions towards LDN 328. This is the first observational attempt to map the magnetic field geometry of a cloud harboring a proto-brown dwarf candidate associated with a sub-parsec scale molecular outflow. On a parsec scale, the magnetic field is found to follow the curved structure of the cloud showing a head-tail morphology. The projected angular offset between the magnetic field and the outflow is found to be around 40 degree. The magnetic field is found to be well ordered over 0.02−0.2 pc scale around L328-IRS. Considering outflow to be the proxy for the rotation axis, the result implies that the rotation axis is tilted by around 40 degree with respect to the local magnetic field (at 0.02 − 0.2 pc scales). The magnetic field strength estimated in the close vicinity of L328-IRS is approx 20 microGauss. Comparing our results with those from the recent simulations, for the estimated strength of the magnetic field, the observed tilt angle (between the magnetic field and rotation axis) alone may not be sufficient to resolve the magnetic breaking problem to facilitate the formation of centrifugally supported disk.


About Speaker: Archana is a Senior Research Fellow at ARIES



[105] Topic: Seeing what we hear: finding electromagnetic counterparts for gravitational wave sources

Speaker: Varun Bhalerao
Affiliation: DST-INSPIRE Faculty Fellow
Date (yyyy-mm-dd): 2014-11-07
Time: 11:00hr
Venue: ARIES Audotorium

Abstract: Within this decade, a global network of advanced gravitational wave detectors including LIGO-India are expected to detect various gravitational wave sources. These detectors can yield certain parameters of the gravitational wave source, but complementary studies in electromagnetic wavelengths are crucial for a complete astrophysical understanding. In this talk, I will talk about the proposed electromagnetic counterparts of these sources, and the extremely challenging problem of detecting them. I will highlight why India forms a key node in this global effort, and discuss prospects of optical, IR, radio and X-ray follow-up from India.


About Speaker: Varun Bhalerao is a young scientist working at IUCAA Pune.



[102] Topic: Investigation of the stellar variability and Rotational Activities in Kepler Field

Speaker: Mr. SOWGATA CHOWDHURY
Affiliation: Tejpur University
Date (yyyy-mm-dd): 2014-10-31
Time: 12:15hr
Venue: Auditorium

Abstract: In this talk, I present the results on the time-series photometric analysis of approximately 15000 stars observed by Kepler space mission. We announce some discoveries such as solar-like oscillations in 83 red giants, 52 eclipsing binary systems etc. We have estimated the rotation periods of 2948 active stars and discuss the distribution of their frequencies and amplitudes. Interestingly, we have found star-spots in several A-type stars and observed that the number of A-type stars with starspots increases with decreasing amplitude. Using asteroseismic technique we have derived the basic astrophysical parameters such as masses, radii and luminosities of the 113 red giants. We have also found many new flares on late type stars, non-radial pulsating variables such as Delta Sct, Gamma Dor stars etc..


About Speaker: Mr. Sowgata Chowdhury is a project student working with Dr. Santosh Joshi since last three months. He has requested extension for next three months to complete his project.



[93] Topic: X-ray flare on 47 Cas

Speaker: Subhajeet Karmakar
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2014-09-09
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: Using XMM-Newton observation, we investigate properties of a flare from very active and poorly known star 47 Cas B. The luminosity at peak of the flare was found to be 4.77×10^30 erg/s, which is ~2 times more than that from a quiescent state. The quiescent state corona of 47 Cas was represented by two temperature plasma: 3.7 and 11.0 MK. The time-resolved X-ray spectroscopy of the flare showed a variable nature of temperature, emission measure and abundances. The maximum temperature during the flare was found to be 72.8 MK. We inferred the size of a flaring loop using hydrodynamic loop model and the length was found to be of 3.3 × 10^10 cm. Using the RGS spectra, density during the flare was found to be 4.0 × 10^10 cm^(-3). The loop scaling laws were also applied in deriving physical parameters of the flaring plasma.


About Speaker: SRF at ARIES



[96] Topic: Multi-wavelength diagnostics of energy transportation and triggering of X1.2 class solar Flare observed on May 15, 2013

Speaker: Aabha Monga
Affiliation: ARIES
Date (yyyy-mm-dd): 2014-09-09
Time: 10:00hr
Venue: New Auditorium

Abstract: We study the energy build-up and trigger processes responsible for a X1.2 class solar flare that occurred in NOAA AR 11748, having βγδ magnetic complexity observed on May15, 2013. The flare was well observed by ground based (Hα ARIES, Nainital) and space borne (SDO, HMI). The flare shows two ribbons structures. Morphology of the flare ribbons shows that the brightening propagates along the southern ribbon. We have noticed several Hα kernels that shows different spatially and temporally evolutionary behavior. On the contrary, we do not find filament associated with this event. Therefore, to explore the driver of instability leading to this highly energetic flare, we study the morphological evolution of the active region using SDO and Hα data. We also study the evolution of photospheric magnetic field parameters from SDO/HMI magnetograms in conjunction to the E/UV emission. From AIA EUV images, we note sets of coronal loops over the active region, which show upward motion with the time. We explicitly note mass ejection and disruption of coronal loops. From this study, we infer that this flare occurred in the lower corona as the coronal loops moved upward which gives the signature of magnetic reconnection beneath the uprising loops.


About Speaker: Abha has entered the 3rd year as ARIES PhD student. This is her JRF to SRF talk.



[94] Topic: Astrometric and Photometric Studies of Star Clusters

Speaker: Devesh PathSaria
Affiliation: ARIES
Date (yyyy-mm-dd): 2014-09-04
Time: 15:30hr
Venue: New Auditorium

Abstract: Astrometry of stars in star clusters was least explored for many decades in the last century until the advent of CCD. Photographic plates were yielding a poor number of stars in star-rich clusters with the epoch gap of many decades. With wide field CCD data, it is now possible to probe much fainter regions of stellar clusters to achieve precise proper motions with the epoch gap now being reduced to a few years. Applications of such studies are numerous. These include, deriving precise fundamental parameters of star clusters using most probable cluster members based on membership probabilities values calculated using proper motions, finding absolute proper motions and using them to understand space motion of a star cluster in the Galaxy. To get precise positions and proper motions for large number of stars in the cluster regions, we need wide and high quality images taken at good (~1 arcsec) seeing conditions. For this purpose, we have selected the two epoch data set taken with wide-field imager mounted on 2.2-m telescope installed at La Silla, Chile. We have used the exclusive software developed by Anderson et al. (2006) to calculate proper motions of the stars in the clusters regions. One of the main aim of our work was to provide proper motions and membership probabilities in the region of globular cluster NGC 6809 (M55) in the wider region and fainter magnitudes than previous studies of the cluster. We have derived precise proper motions and astrometric membership probabilities for 12600 stars down to V ~20 mag in 26X22 area. The measurement error in proper motions for the stars of V < 17 mag is 2.0 mas/yr, gradually increasing up to ~ 3 mas/yr at V = 20 mag. We also provide the membership probabilities for the published variables and X-ray sources in the cluster region. All the known SX Phe and RR Lyrae found in our data are most probable cluster members based on our membership catalogue. Open cluster NGC 3766 was studied for the first time with the aim of astrometry. Proper motions and membership of ~2500 stars were estimated and the membership catalogue was used to determine age and mass function slop of the cluster using stars with membership probability >70%. Mass segregation was observed for NGC 3766 and the cluster was found to be dynamically relaxed. To understand the space motion of the globular cluster NGC 6121 (M4), we used Southern Proper Motion (SPM) catalogue in combination with 2MASS catalogue to determine space velocity components of the cluster. The cluster was found to be having a disk-like kinematics. In addition to this, we did time series analysis of the globular cluster NGC 4590 (M68) using the CCD data taken with 104-cm Sampurnand telescope and searched variable stars in its area. We found 40 known and 9 new probable variable stars for which we present phased light curves and periods. In the present talk, I will also state my future research plans.


About Speaker: Devesh has completed six years as PhD student in ARIES. Recently submitted his thesis in Raipur University. This is his post doc evaluation talk.



[92] Topic: Models of disk and jet variability in AGN

Speaker: Dr. Prashanth Mohan
Affiliation: IIA, Bangalore
Date (yyyy-mm-dd): 2014-07-31
Time: 15:30hr
Venue: Auditorium

Abstract: We address optical/UV and X-ray variability attributable to orbital signatures from an emitting blob on the accretion disk or in the relativistic jet. Disk based signatures include the quasi-periodic oscillations (QPOs) and its quality factor, and a break frequency in the power spectral density (PSD) shape of the light curve which are used to constrain black hole mass, spin and the emission region size. A general relativistic (GR) model of jet variability due to an orbiting blob in helical motion along a funnel (or cone) shaped magnetic surface anchored to the accretion disk is then presented. Simulated light curves include Doppler and gravitational shifts, aberration, light bending and time delay. We find an increased amplitude (~ 12 %); beaming and a systematic phase shift in the light curve compared to that from an earlier special relativistic model. These results strongly justify the use of a realistic magnetic surface geometry and a fully relativistic calculation. These models are applicable to the study of disk and jet variability in radio, optical and X-ray emission from sources including AGN, X-ray binaries, accreting neutron stars and supermassive binary black holes.


About Speaker: Dr. Prashanth Mohan is a Post Doctoral Researcher of IIA, Bangalore.



[90] Topic: Multi-band Optical/NIR Variability Studies of the Blazar 3C 454.3

Speaker: Ms. Aditi Agarwal
Affiliation: ARIES
Date (yyyy-mm-dd): 2014-07-28
Time: 11:30hr
Venue: Auditorium

Abstract: We have carried out photometric monitoring of the bright flat spectrum radio quasar 3C 454.3, which has exhibited remarkably high activity and pronounced variability at all wavelengths since 2001, to search for optical variability on a wide range of timescales. CCD magnitudes in B, V, R and I pass-bands were determined from 63 optical observations made during 2011 – 2014, with an average length of ∼ 4 h each, at seven optical telescopes: four in Bulgaria, one in Greece, and two in India. We measured multiband optical flux and color variations on diverse timescales. Discrete correlation functions were computed among B, V, R, and I observations, to search for any time delays. We found weak correlations in some cases with no significant time lags. The structure function method was used to estimate any characteristic time-scales of variability. We also investigated the spectral energy distribution of 3C 454.3 using B, V, R, I, J and K pass-band data. We found that the source almost always follows a bluer-when-brighter trend. We discuss possible physical causes of the observed spectral variability.


About Speaker: Aditi is 2nd year Ph.D. student in ARIES.



[88] Topic: Study of surface ozone, oxides of nitrogen, carbon monoxide, and methane at a site in the Indo Gangetic Plain region

Speaker: ADWAIT SHUKLA
Affiliation: INDIAN SCHOOL OF MINES, DHANBAD.
Date (yyyy-mm-dd): 2014-07-11
Time: 14:00hr
Venue: Seminar Hall

Abstract: Observations of surface ozone, CO, NOx, CH4 and NMHCs were made at a semi urban site (Pantnagar) in the Indo-Gangetic plain region. Ozone diurnal variations are characterized by daytime photochemical buildup. Changes in ozone show a systematic increase from January 2014 to June 2014. Diurnal patterns in CO, NOx and THC also follow the characteristics of somewhat polluted site. Daily average values in CO, NOx, and THC follow a reverse trend when compared with that in ozone. Based on the above study it is concluded that - Oxidation of CO and THC in the troposphere results in the production of Ozone. So, emissions of CO and THC must be reduced so as to deal with the surface air pollution problem. In this process NOx plays a very critical role. It is also suggested to carry out a high resolution model study for this region to get better information on the different tropospheric processes occurring in this region.


About Speaker: He is Project Student under Academy Program



[81] Topic: Observing multiply imaged quasars with the 4m International Liquid Mirror Telescope

Speaker: Prof. Jean Surdej
Affiliation: Institute of Astrophysics and Geophysics, Liège University, Belgium
Date (yyyy-mm-dd): 2014-06-11
Time: 15:30hr
Venue: Auditorium

Abstract: I shall first remind the basic properties of gravitational lens systems and how these can be used to derive interesting astrophysical and cosmological parameters. I shall specially address the case of symmetric gravitational lens systems for which such parameters can be derived irrespective of the assumed lens model. I shall then describe the 4m International Liquid Mirror Telescope project and explain how this telescope, to be be soon erected on the ARIES site in Devasthal (Uttarakhand), will be used to detect and monitor approximately 50 cases of multiply imaged quasars.


About Speaker: Prof. Jean Surdej is professor at University of Liège, Belgium.



[80] Topic: Seasonal inhomogeneity in cloud precursors over Gangetic Himalayan region during GVAX campaign

Speaker: Dr U C Dumka
Affiliation: ARIES
Date (yyyy-mm-dd): 2014-06-10
Time: 15:30hr
Venue: Auditorium

Abstract: Atmospheric aerosols act as key elements of cloud microphysics, hydrological cycle and climate by serving as cloud condensation nuclei (CCN). The present work analyses simultaneous measurements of number concentration of CCN (NCCN) and condensation nuclei (NCN) obtained at Nainital, in the Gangetic-Himalayan (GH) region, during the frameworks of Ganges Valley Aerosol Experiment (GVAX), June, 2011 to March, 2012.


About Speaker: Scientist at ARIES



[79] Topic: Scattering and absorption properties of near-surface aerosol over Gangetic-Himalayan region, India using Atmospheric Radiation Measurement Mobile Facility

Speaker: Dr U C Dumka
Affiliation: ARIES
Date (yyyy-mm-dd): 2014-06-06
Time: 15:30hr
Venue: Auditorium

Abstract: Knowledge of light scattering and absorption properties of atmospheric aerosols is of vital importance in evaluating their types, sources and estimating the radiative forcing of climate. This is of particular interest over the Gangetic-Himalayan (GH) region due to large aerosol loading over the plains and the uplift over the Himalayan range causing serious effects on atmospheric heating, glaciology and monsoon circulation. In this respect, Ganges Valley Aerosol Experiment (GVAX) was initiated over the region aiming to examine the aerosol properties, source regions, uplift mechanisms and aerosol-cloud interactions. Present study examine the temporal (monthly, seasonal) evolution of scattering and absorption coefficients, their wavelength dependence, role of the Indo-Gangetic plains (IGP), boundary-layer dynamics and long-range transport in the aerosol uplift over the Himalayan foothills.


About Speaker: Scientist at ARIES



[78] Topic: Polarimetry: a powerful diagnostic tool in astronomy

Speaker: Prof. U. C. joshi
Affiliation: PRL, Ahmedabad
Date (yyyy-mm-dd): 2014-06-03
Time: 15:30hr
Venue: Auditorium

Abstract: Every astronomical object is polarized to some degree and therefore, astronomical polarimetry gives more information then imaging/ spectroscopy alone. Polarization ie the vector properties of (scattered) starlight depend on the physical circumstances of the location where the light originate. Many properties of scattering dust clouds can be obtained through polarimetry: the sizes, shapes and chemical composition of the scatterers. Even the content, structure and stratification of the atmosphere of some of the stars, planets or exoplanets can, in principle, be characterised without optically resolving them. Another important and unique capability of polarimetry is the measurement of magnetic fields. Astronomical polarimetry has, therefore, unique capability. In this talk basics of polarimetry along with polarization studies in PRL on a few different kind of sources will be discussed.


About Speaker: Prof. U. C. Joshi is retired professor of PRL, Ahmedabad. His has diverse research interests: AGN, start clusters, planetary science, instrumentation, etc.



[76] Topic: PHASE-RESOLVED XMM-NEWTON AND SWIFT OBSERVATIONS OF WR 25

Speaker: Jeewan Ch Pandey
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2014-05-05
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: In this talk I will present an analysis of long-term X-ray and optical observations of the Wolf-Rayet binary WR 25. Using archival data from observations with the XMM-Newton and the Swift observatories spanning over ~10 years, we show that WR 25 is a periodic variable in X-rays with a period of 208 +/- 3 days. X-ray light curves in the 0.5-10.0 keV energy band show phase-locked variability, where the flux increased by a factor of ~2 from minimum to maximum, being maximum near periastron passage. The light curve in the soft energy band (0.5-2.0 keV) shows two minima indicating the presence of two eclipses. However, the light curve in the hard energy band (2.0-10.0 keV) shows only one minimum during the apastron passage. The X-ray spectra of WR 25 were explained by a two-temperatures plasma model. Both the cool and the hot plasmas were constant at 0.628+/-0.008 and 2.75+/-0.06 keV throughout an orbital cycle, where the cooler plasma could be due to the small scale shocks in a radiation driven outflow and the high temperature plasma could be due to the collision of winds. The column density varied with the orbital phase and was found to be maximum after the periastron passage, when the WN star is in front of O star. The abundances of WR 25 were found to be non-solar. Optical V-band data of WR 25 also show the phase-locked variability, being at maximum near periastron passage. The results based on the present analysis indicate that WR 25 is a colliding wind binary where the presence of soft X-rays is attributed to individual components; however, hard X-rays are due to the collision of winds.


About Speaker: Scientist at ARIES



[77] Topic: PHASE-RESOLVED XMM-NEWTON AND SWIFT OBSERVATIONS OF WR 25

Speaker: Jeewan Ch Pandey
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2014-05-05
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: In this talk I will present an analysis of long-term X-ray and optical observations of the Wolf-Rayet binary WR 25. Using archival data from observations with the XMM-Newton and the Swift observatories spanning over ~10 years, we show that WR 25 is a periodic variable in X-rays with a period of 208 +/- 3 days. X-ray light curves in the 0.5-10.0 keV energy band show phase-locked variability, where the flux increased by a factor of ~2 from minimum to maximum, being maximum near periastron passage. The light curve in the soft energy band (0.5-2.0 keV) shows two minima indicating the presence of two eclipses. However, the light curve in the hard energy band (2.0-10.0 keV) shows only one minimum during the apastron passage. The X-ray spectra of WR 25 were explained by a two-temperatures plasma model. Both the cool and the hot plasmas were constant at 0.628+/-0.008 and 2.75+/-0.06 keV throughout an orbital cycle, where the cooler plasma could be due to the small scale shocks in a radiation driven outflow and the high temperature plasma could be due to the collision of winds. The column density varied with the orbital phase and was found to be maximum after the periastron passage, when the WN star is in front of O star. The abundances of WR 25 were found to be non-solar. Optical V-band data of WR 25 also show the phase-locked variability, being at maximum near periastron passage. The results based on the present analysis indicate that WR 25 is a colliding wind binary where the presence of soft X-rays is attributed to individual components; however, hard X-rays are due to the collision of winds.


About Speaker: Scientist at ARIES



[74] Topic: Influence of short period gravity waves in vertical transport of aerosols during daytime boundary layer evolution over Central Himalayan region: A case study

Speaker: K K Shukla
Affiliation: ARIES
Date (yyyy-mm-dd): 2014-05-01
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: In this study, we present a case of 16 October 2011 to show the first observational evidence of influence of short period gravity waves in aerosol transport during daytime over Central Himalayan region. Doppler lidar data is utilized to address the daytime boundary layer evolution and related aerosol dynamics over the site. Boundary layer height is estimated by wavelet covariance transform method and found to be ~ 0.7 km AGL. AOD observations during daytime revealed an asymmetry showing clear enhancement during afternoon hours as compared to forenoon. Interestingly, Fourier and wavelet analysis showed similar 50-90 min short period gravity wave signatures dominant during afternoon hours. Moreover, our observations showed gravity waves are dominant within boundary layer implying that the daytime boundary layer dynamics is playing a vital role in transporting the aerosols from surface to boundary layer top. Similar modulations are also evident in surface parameters like Temperature, RH and wind speed indicating these waves are associated with the dynamical aspects over Himalayan region. Finally, time evolution of RHI snapshots during daytime showed strong upward velocities especially during afternoon hours implying that the transportation of aerosols by convective processes are dominant through short period gravity waves to boundary layer top over the site. Our observations should shed some light in the current understanding of wave induced daytime convective boundary layer dynamics over Himalayan region.


About Speaker: Research Scholar working in the field of Atmospheric Sciences



[71] Topic: Photometric evolution of type IIP supernova SN 2004dj

Speaker: Rohit Patil
Affiliation: IIST
Date (yyyy-mm-dd): 2014-04-10
Time: 15:30hr
Venue: Auditorium

Abstract: Photometric evolution of a type IIP supernova SN 2004dj is studied in this project.


About Speaker: Rohit Patil is a final semester B. Tech. student at IIST Trivandrum.



[72] Topic: Open Star Clusters in galaxy

Speaker: Rohit Nagaori
Affiliation: IIST
Date (yyyy-mm-dd): 2014-04-10
Time: 16:00hr
Venue: Auditorium

Abstract: The aim of our project is to study the statistical distribution of the various cluster parameters and the correlation between them. For that purpose, we have prepared a dataset consisting of the various parameters of clusters with the help of Kharchenko et al.(2013) catalogue. We have studied the statistical distribution of parameters such as diameter, age, metallicity as well as correlations between various parameters such as mass with respect to age and diameter of clusters. We also studied the distribution of open clusters in longitudes as well as their spatial distribution in galactic plane.


About Speaker: Rohit Nagaori is a final semester B. Tech. student at IIST Trivandrum.



[70] Topic: Variations in Hydrocarbons over the central Himalayas and the Indo-Gangetic Plain.

Speaker: Tapaswini Sarangi
Affiliation: ARIES
Date (yyyy-mm-dd): 2014-03-31
Time: 14:30hr
Venue: New Auditorium

Abstract: Thesis material of Tapaswini.


About Speaker: Tapaswini Sarangi submitted her thesis done under Dr. Manish Naja. She was a project student under Dr. Naja, and now has applied for regular ARIES post-doctoral position.



[66] Topic: Probing energetics of solar flares from multi-wavelength emission

Speaker: Arun Kumar Awasthi
Affiliation: Physical Research Laboratory
Date (yyyy-mm-dd): 2014-01-10
Time: 15:30hr
Venue: New Auditorium

Abstract: Solar flares are sudden and bursty emissions from the atmosphere of the Sun. Temporal evolution of the flares consists of three phases viz. Precursor, impulsive and gradual. Latter two phases have been studies extensively, however underlying physical processes of energy release during the precursor phase are not yet fully understood owing to lack of high cadence observations. I will present the current understanding on this phase of flare emission as well as my work on the same. Further, I will also present the thermal characterisation of flare plasma in view of its iso/multi-thermal nature.


About Speaker: Completed his PhD from Physical Research Laboratory, and applied for post-doctoral position in ARIES.



[65] Topic: Near-infrared study of classical novae

Speaker: Ashish Raj
Affiliation: Physical Research Laboratory
Date (yyyy-mm-dd): 2014-01-07
Time: 15:30hr
Venue: New Auditorium

Abstract: The classical novae are close binary systems with a late-type main sequence star (the secondary) transferring material via Roche lobe overflow to a companion star (the primary). Novae brighten by 10 - 12 magnitudes in a few hours and subsequently fade back to the original faint level over a period lasting several months to years. The results obtained from the IR observations will be presented. The system parameters of the observed novae, like the distance to the nova, absolute magnitude, expansion velocity of the ejecta, mass of the ejecta and gas to dust ratio are estimated. The dust formation and the detection of first overtone emission bands of CO in these novae will be discussed.


About Speaker: Dr. Ahish Raj is a post-doc in PRL, and has applied for post-doctoral position in ARIES.



[62] Topic: DISTANCE DETERMINATION TO EIGHT GALAXIES USING EXPANDING PHOTOSPHERE METHOD

Speaker: Subhash Bose
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-12-27
Time: 15:30hr
Venue: Auditorium

Abstract: Type IIP supernovae are recognized as independent extragalactic distance indicators, however, keeping in view of the diverse nature of their observed properties as well as the availability of good quality data, more and newer events need to be tested for their applicability as a reliable distance indicators. We use early photometric and spectroscopic data of eight type-IIP SNe to derive distances to their host galaxies using the expanding photosphere method (EPM). For five of these, EPM is applied for the first time. In this work, we improved EPM application by using synow estimated velocities and by semi-deconvolving the broadband filter responses while deriving color temperatures and black-body angular radii. We find that the derived EPM distances are consistent with that derived using other redshift independent methods.


About Speaker: Mr. Subhash Bose is SRF at ARIES.



[63] Topic: Latitudinal variability in CALIPSO derived aerosol vertical profile over the central Himalayas and IGP

Speaker: Pratima Gupta
Affiliation: B H U, Varanasi
Date (yyyy-mm-dd): 2013-12-24
Time: 11:00hr
Venue: Auditorium

Abstract: In this study we analyzed data collected by the space-born LiDAR (CALIOP) on-board the satellite CALIPSO. The latitudinal variability in vertical distribution of aerosols (backscatter coefficient and depolarization ratio) has been studied during January to December, for the year 2012.


About Speaker: Miss Pratima is a student of M.Sc. Tech. final year at BHU Varanasi



[64] Topic: VERTICAL PROFILING OF AEROSOL OVER MANORA PEAK USING MPL: GVAX CAMPAIGN

Speaker: Shishir Kumar Singh
Affiliation: B H U, Varanasi
Date (yyyy-mm-dd): 2013-12-24
Time: 11:30hr
Venue: Auditorium

Abstract: The variability in aerosol vertical distribution during the transition phase from winter to spring season was studied. We incorporated the data collected by the micro-pulse LiDAR (MPL) (Feb-March 2012) operated as part of GVAX-campaign. A comparison of aerosol backscatter profile obtained from GVAX MPL and one other collocated LiDAR (LAMP) at ARIES has also been studied.


About Speaker: Mr. Shishir is a student of M.Sc. Tech. final year at BHU Varanasi



[61] Topic: A spectroscopic study of cool pulsating A and F stars within Indo-Russian DST-RFBR project

Speaker: Dr. Evgeney Semenko
Affiliation: Special Astrophysical Observatory (SAO), Russia,
Date (yyyy-mm-dd): 2013-12-13
Time: 15:30hr
Venue: Auditorium

Abstract: An international bilateral Indo-Russian project is being supported by DST, Govt of India and RFBR, Russia aiming for the complex study of pulsation in A and F stars those discovered under the Nainital-Cape photometric survey. The current talk is based on the new results of spectroscopic study of three cool A stars with different rotational velocity. We have shown that chemical abundances of this programme objects are typical for delta Sct-type and metallic-line stars.


About Speaker: Dr. Semenko is working as a researcher/scientist at SAO, Russia.



[59] Topic: Identification of Coronal Funnels On the Basis of Doppler Velocity, Line Width and Density in the Quiet Sun and Coronal Hole

Speaker: Pradeep Kayshap
Affiliation: ARIES, Nainital, India
Date (yyyy-mm-dd): 2013-12-10
Time: 15:30hr
Venue: New Auditorium

Abstract: Coronal funnels, which originates from the networks at the photosphere, have great importance in terms of the mass up flows from lower to upper solar atmosphere. We have studied a North Polar Coronal Hole (NPCH) observation, which was observed on 10 October 2007 by Extreme Ultraviolet Imaging Spectrometer (EIS) onboard Hinode, to identify the coronal funnels in the observed region. By the Gaussian fitting technique, we have estimated three basis parameters (e.g., Doppler velocity, FWHM, Intensity) on each location of the observed region. Extra FWHM locations (i.e., above a threshold level) have been identified in quiet sun (QS), quiet sun with coronal hole boundary (QSCH) and coronal hole (CH) regions. For the density measurement, we have used the intensity ratio of two density sensitive Fe XII lines and CHIANTI atomic data. On the basis of the variations of the parameters (e.g.,intensity,Doppler velocity,density), we have shown that the excess width regions in the quiet sun are the coronal funnels. In the QSCH and CH regions, we have not found the favorable results to say that the excess width locations in these regions are the coronal funnels. We have also found that plasma up flow starts at log 6.0 K and log 5.8 K in the quiet sun and coronal holes respectively. Study of the temperature dependent behaviour of the nonthermal velocity is a forefront research in the solar physics now-a-days. In present analysis, nonthermal velocity decreases from Transition Region (TR) up to corona in the coronal hole as well as quiet sun. With the help of some previous results of nonthermal velocities, we have found that nonthermal velocity increase with temperature but after a certain temperature it decrease further. We have shown that Alfven wave propagation and dissipation as well as the prevalent occurrence of nano-flares at O VI formation temperature are two most probable responsible mechanisms for the explanation of nonthermal velocity.


About Speaker: Pradeep Kayshap is the SRF working in the field of Solar Physics.



[60] Topic: Nonlinear analysis of Spatiotemporal data: Applications in Biology

Speaker: Naveen Kumar Bhatraju
Affiliation: University of Delhi
Date (yyyy-mm-dd): 2013-11-27
Time: 11:00hr
Venue: Auditorium

Abstract: Weather, climate, earthquake and forex are a few examples of a vast list of complex real world dynamical systems where forecast of extreme events that would occur in future is of great value. Accurate prediction of such events requires a critical understanding of the dynamics of these complex systems. The introduction of nonlinear time series analysis has given significant insights into the temporal patterns in the dynamics of the aforementioned systems. There are many nonlinear analysis methods proposed for analyzing a given time series including, but not limited to, fluctuation analysis, synchronization, entropy and recurrence analysis. In the present talk, I will be discussing some of the aforementioned techniques which were used by us for analysis of biological and physical systems.


About Speaker: Working at University of Delhi.



[57] Topic: Synoptic Maps of Solar Vector Magnetic Fields from VSM/SOLIS instrument at NSO: First Results

Speaker: Sanjay Gosain
Affiliation: NSO, Tucson, USA
Date (yyyy-mm-dd): 2013-11-14
Time: 15:30hr
Venue: New Auditorium

Abstract: Full-disk vector magnetic field measurements of the Sun are now routinely carried out at National Solar Observatory, Tucson, USA, since the beginning of cycle 24. In order to understand the role of magnetic field in production of flares and coronal mass ejections (CMEs) as well as its evolution with 11 year solar cycle we need continuous uninterrupted measurements of solar magnetic field. Space based measurements by missions like SOHO/MDI and SDO/HMI have limited lifetime and are prone to non-repairable failures. Ground based measurements on the other hand have long lifetimes and can be easily repaired and maintained. I will describe the new fulldisk observations of the vector magnetic fields by SOLIS VSM at NSO and the new type of synoptic maps that are produced from these observations . I will also present few results from these measurements relevant to large scale patterns of magnetic fields and their helicity.


About Speaker: Dr. Sanjay Gosain is working at NSO, Tucson, USA. He is well known for the observations and modelling of the solar photospheric magnetic fields, and their role in the various types of eruptive phenomena.



[56] Topic: SOLAR FILAMENTS AS INDICATORS OF CME PROBABILITY

Speaker: Boris Filippov
Affiliation: Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagatio
Date (yyyy-mm-dd): 2013-11-12
Time: 15:30hr
Venue: New Auditorium

Abstract: The onset of a CME is not preceded by any specific form of activity that could be recognized several days before the event. The cause of eruption is more likely in properties of coronal magnetic field equilibrium, possibly in the rapid growth of instability. The most probable initial magnetic configuration of a CME is a flux rope consisting of twisted field lines which fills the whole volume of the dark cavity stretched in the corona along the photospheric polarity inversion line. A coronal cavity is well recognized in coronal images only when its axis is directed along the line-of-sight; otherwise it is screened by surrounding bright coronal loops. Cold dense prominence matter accumulates in the lower parts of helical flux tubes, which serve as magnetic traps in the gravitation field. So, prominences and filaments are good tracers of the flux ropes in the corona long before the beginning of eruption. A twisted flux rope is held by the tension of field lines of photospheric sources until parameters of the system reach critical values and catastrophe happens. The flux rope height above the photosphere is one of these parameters and it is revealed by the height of the filament. There is a critical height in the given coronal magnetic field that the flux rope cannot exceed being in stable equilibrium. We found that many eruptive prominences were near the limit of stability a few days before eruptions. A filament eruption on 2010 October 21 observed from three different viewpoints by the Solar Terrestrial Relations Observatory and the Solar Dynamic Observatory is analyzed in detail by invoking also data from the Solar and Heliospheric Observatory and the Kanzelhoehe Solar Observatory. The position of the filament just before the eruption at the central meridian not far from the center of the solar disk was favorable for photospheric magnetic field measurements in the area below the filament. Because of this, we were able to calculate with high precision the distribution of the coronal potential magnetic field near the filament. We found that the filament began to erupt when it approached the height in the corona where the magnetic field decay index was greater than 1. We believe that a comparison of the measured heights of filaments with the calculated critical heights could be a basis for predicting filament eruptions and following CMEs.


About Speaker: Dr. Boris Fillipov is the head of laboratory of solar physics at IZMIRAN, Troitsk, Russia. He is well known for the modelling and observations of the solar eruption pre-cursors, e.g., solar filaments. He is visiting ARIES as a Russian PI of ongoing DST-RFBR project.



[55] Topic: GUI and Command Interface Design for 3.6m Observatory Control Software

Speaker: Bhavya Kaushik
Affiliation: Manipal University Jaipur
Date (yyyy-mm-dd): 2013-10-11
Time: 15:30hr
Venue: Auditorium

Abstract: A primary design of GUI of the Observatory Control Software for 3.6m Telescope and command interface design have been implemented using Qt framework. This work will be discussed in this talk.


About Speaker: Mr. Bhavya Kaushik is student of M.Tech. final year at Manipaul University Jaipur. He is working as project trainee at ARIES for last two months. He is working on software development for 3.6m Telescope. He is working on GUI and command interface design and OCS-TCS interface design.



[52] Topic: Significance of MHD Seismology in the Astrophysical Plasma

Speaker: Dr. A.K. Srivastava
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2013-10-08
Time: 15:30hr
Venue: New Auditorium

Abstract: The stable fluxtubes possessing the ionized plasma coupled with magnetic field, when perturbed from their equilibrium, can support the evolution of various tubular MHD modes (e.g., kink, sausage, torsional, and slow waves). These modes are now ubiquitous in the various astrophysical plasmas, e.g., the solar and stellar coronae. The detection of these MHD modes are important keeping the view of their physical properties that can be utilized in deriving many crucial local plasma conditions where they excite. In the present paper, we review the state-of-art of this continuously developing new sub-field in the Astrophysics. We present the detection of MHD modes in coronae of Sun and Sun-like stars and use of the principle of MHD seismology to understand some local physical conditions there (e.g., magnetic field) that can not be determined by classical methods. We conclude that the refinement in the MHD seismology of solar corona is also providing the best analogy to develop the stellar seismology of magnetically active similar stars to deduce the local physical conditions of their coronae.


About Speaker: Dr. A.K. Srivastava is working in ARIES as a Scientist in the field of Solar Physics. His primary research interest is to understand the transients (e.g., spicules, jets, and large-scale eruptions) and MHD phenomena (waves, heating processes, reconnection, instabilities) in the solar atmosphere under observational and theoretical base-line.



[51] Topic: Errors in astronomical observations due to motion of the observer and the physical justification against dark flow

Speaker: Mukesh Kumar Vyas
Affiliation: Aries
Date (yyyy-mm-dd): 2013-10-01
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: The talk is designed to present my initial work done in theoretical cosmology. The analysis has two implications, The effect of the motion of the observer induces a certain amount of error in the observational astronomy. The relation of this effect is derived and a need for correction in the position (up to 5% of a degree in angular shift in the coordinates)of cosmic objects is proposed due to our cosmic motion around the Milky Way. As the second implication, the results of the analysis will help us to solve the debate over physical existence of the dark flow and and our motion under CMB dipole with predicted speed 630km/sec. Primary outcomes provide negative results for the validity of Dark flow. If further analysis of cosmic structure follows primary indications (which is the next step of the work) it will be a strong evidence against multiverse concept in modern cosmology.


About Speaker: Research scholar at ARIES



[49] Topic: Black hole Accretion in Schwarzschild Metric

Speaker: Golam Mafuz
Affiliation: IIT Kharagpur
Date (yyyy-mm-dd): 2013-09-20
Time: 15:30hr
Venue: New Auditorium

Abstract: For any specific energy and specific angular momentum there may exist multiple critical point. For a specific energy and angular momentum, I have plotted the Mach number as a function of distance.


About Speaker: Completed MSc from IIT Kharapur.



[48] Topic: REVISITING NEWTON’S LAWS: POSSIBLE MODIFICATION AND AMAZING COSMOLOGICAL CONSEQUENCES

Speaker: Amitabha Ghosh
Affiliation: Platinum Jubilee Senior Scientist of The National Academy of Sciences India & Ho
Date (yyyy-mm-dd): 2013-09-13
Time: 11:00hr
Venue: ARIES Auditorium

Abstract: Newton’s Laws of motion and universal gravitation constitute the foundation of almost all branches of science and engineering. Mostly, these are introduced at the senior levels in the schools and the students practice applying these laws to many problems. Apparently these laws look fine and without any problem. But as one rarely returns to ponder over these laws seriously at senior levels, the serious problems associated with these laws remain unnoticed. This lecture proposes a return to the Newton’s Laws of motion and universal gravitation to examine the situation. In the first part of the talk the difficulties with these laws will be discussed and some modifications will be suggested. It will be shown how the difficulties melt away and very profound consequences emerge. In the second part of the talk the modified law will be applied to a number of astrophysical and solar system mechanics problems. It will be very interesting to see how in all cases the proposed extended Newton’s laws can resolve a number of unexplained phenomena and finally results in a very profound consequence so far as the model of our universe is concerned.


About Speaker: Amitabha Ghosh received his Bachelor of Engineering and Master of Engineering degrees from Bengal Engineering College, Shibpur, (Calcutta University) in 1962 and 1964, respectively. He joined the Mechanical Engineering Department of this college as a Lecturer in 1965 May and continued his doctoral research finally receiving the Doctorate degree from Calcutta University in 1969. He joined IIT Kanpur in January 1971 as an Assistant Professor of Mechanical Engineering and became Professor in 1975 June. From 1977 to 1978 he spent at the Technical University Aachen with Alexander von Humboldt Foundation senior fellowship. From 1997 to 2002 he served IIT Kharagpur as the Director and subsequently returned to his Professorial position at Kanpur where he continued up to 2006 till his retirement. After retirement from IIT Kanpur he worked as a Senior Scientist of the Indian National Science Academy, New Delhi and Honorary Distinguished Professor at both IIT Kanpur and Bengal Engineering & Science University, Shibpur. Currently he is a Platinum Jubilee Senior Scientist of the National Academy of Sciences, India, Allahabad and also an Honorary Distinguished Professor at Bengal Engineering & Science University, Shibpur. His research and academic interests are in Basic Mechanics, Kinematics and Dynamics, Advanced Manufacturing and Robotics. He has guided more than 75 M Tech and 18 PhD students and published about 125 research papers.



[47] Topic: Confined Partial Filament Eruption and its Reformation within a Stable Magnetic Flux Rope

Speaker: Navin C Joshi
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-09-10
Time: 15:30hr
Venue: ARIES AUDITORIUM

Abstract: In this paper, we present an observation of the confined upward motion of core cooler plasma of a filament that remains within a stable magnetic configuration during its activation. Later it exhibits a rapid reformation along the same magnetic channel within ≈2 hours after the eruption on 4 August 2012. Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), Solar TErrestrial RElations Observatory/Sun Earth Connection Coronal and Heliospheric Investigation (STEREO/SECCHI) and Global Oscillation Network Group (GONG) Hα observations have been analyzed to investigate the physical mechanism of this plasma dynamics of filament, which shows the sinistral magnetic orientation with positive sign of magnetic helicity. From the GONG Hα observations, we find that the filament plasma gets into its dynamic motion at around 11:20 UT from the middle part of the filament towards the north-west direction with an average speed of ≈100 km/s. Small brightening underneath of it shows possibly the signature of low atmospheric reconnection below the filament eruptive part. In SDO/AIA 171 A images, we observe an activation of right-handed helically A twisted magnetic flux rope that contains the filament material and confines it during its dynamical motion. The motion of the cool plasma of the filament core stops after traveling a distance of around ≈215 Mm from the point of eruption towards north-west. Some of the plasma moves towards right foot point of the flux rope, while most of the plasma returnes back after 12:00 UT towards the left foot point in order to reform the filament with an average speed of ≈60 km/s within the stable magnetic structure. From the coronal magnetic field decay index n calculation near the flux rope axis, it is evident that the whole filament axis lies within the domain of stability (i.e., n < 1), which infers the filament stability in spite of strong disturbances at its eastern foot point.


About Speaker: Dr. Navin C Joshi is post-doc at ARIES and works in a field of Solar Physics.



[46] Topic: Studies of dust properties and the importance of magnetic fields using optical and NIRpolarimetry.

Speaker: C. Eswaraiah
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-09-06
Time: 11:00hr
Venue: ARIES AUDITORIUM

Abstract: I will present results based on the work done for the last six months during my PDF tenure. During this period, I have worked on various projects related to studies of dust grain properties and the role of magnetic fields in connection with the formation of clouds, their evolution and collapse and finally the star-formation processes. I briefly present about the structure function analysis on the measured polarization angles towards a dark globule LDN1570 and its significance in understanding the importance of magnetic fields in rendering the cloud stability against gravity and turbulence. Then, I will present our recent results based on the near-infrared (NIR) polarimetric observations of a starforming region NGC 1893. Analysis yields important clues regarding the uniform alignment of dust grains (and hence high polarization efficiency) in accordance with our previous results based on optical polarimetry (Eswaraiah et al. 2011). I will discuss how the magnetic field orientation inferred using J and H-band polarization angles may give important clues regrading the impact of ionizing radiation on the surrounding medium, and the correlation between the magnetic field structure with the starformation activity in NGC 1893 region. I will also present the preliminary results based on the


About Speaker: He is Post -doc at ARIES and working on polarimetric study of star forming regions.



[44] Topic: Deep optical and near-infrared survey of the stellar contents of Sh2-311 region

Speaker: Ram Kesh Yadav
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-09-03
Time: 15:30hr
Venue: ARIES auditorium

Abstract: The stellar content and environment of the Sh2-311 region have been studied using the deep optical and near-infrared (NIR) observations. The region contains three clusters, viz. NGC 2467, Haffner 18 and Haffner 19. NGC 2467 and Haffner 19 are found to be located in the Perseus arm at the distances of 5.0±0.4 kpc and 5.7±0.4 kpc, respectively whereas cluster Haffner 18 is located at the distance of 11.2±1.0 kpc. The NGC 2467 and Haffner 19 clusters might have been formed from the same molecular cloud, whereas the the cluster Haffner 18 is located in the outer galactic arm Norma-Cygnus. On the basis of deep NIR observations we have identified 73 young stellar sources (YSOs) with NIR-excess stars. The estimated ages and masses of these YSOs are in the range of 0.1-5.0 Myr and 0.3-3.5 M_sun, respectively suggesting that these sources could be T-Tauri stars. Spatial distribution of YSOs shows that some of the YSOs are distributed along the 8 µm emission contours derived from Spitzer IRAC observation, whereas a significant number of YSOs are clustered towards the eastern border of the 8 µm contours. The dynamical age of the ionized region, spatial distribution of YSOs, and mean age of the YSOs, (∼1.3 Myr) suggest for a triggered star formation in the Sh2-311 region probably due to the collect and collapse process. The IMF of the YSOs is found to be flat (Γ=0.08±0.22).


About Speaker: SRF at ARIES



[43] Topic: Study of Solar Eruptive Phenomena and their Interplanetary Consequences

Speaker: Navin Chandra Joshi
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-08-27
Time: 15:30hr
Venue: New Auditorium

Abstract: In this talk, I will discuss my main research work during last one year in which I have contributed significantly. During the last one year I actively involved in various research and developmental activities in Solar Group at ARIES. We have studied a huge solar eruptive event on 23 January 2012 using multiwavelength data set and found the evidence of CME-CME interaction, which produced a huge solar energetic particle event of cycle 24 (paper I). I will also discuss another work in which I have investigated the relationship between the asymmetric filament eruption and coronal downflows and interpreted my observations with the self-consistent model of flux rope (paper 2). The filament stability and its quick reformation (paper 3) will also discussed in this talk. Apart form this I will also present my research and developmental activity, conference attended, paper presented and my future work at ARIES.


About Speaker: Post Doctoral Fellow in ARIES, who has completed 2 years.



[40] Topic: Study of the aerosol characteristics over the central Himalayas

Speaker: Hema Joshi
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-08-22
Time: 16:00hr
Venue: ARIES Auditorium

Abstract: Ground based observations of AOD, aerosols number concentrations and BC are made at Nainital (29.4 °N, 79.5 ºE, 1958 m amsl), a high altitude site in the central Himalayas, under ISRO-ARFI project. Surface observations of BC and AOD are also made at Pantnagar (29.0 °N, 79.5 ºE, 231 m amsl) under this project. Generally, AOD, aerosols number concentrations and BC shows a major peak during spring followed by autumn at Nainital. The BC mass concentration is found to be maximum (1.35 ± 0.74 µgm-3) in spring (Mar-May) and minimum during summer/monsoon (Jun-Aug) season (0.69 ± 0.52 µgm-3). Further BC is 0.90 ± 0.60 µgm-3 in autumn (Sep-Nov) and 1.00± 0.65 µgm-3 in winter (Dec-Feb) season at Nainital. The concentration weighted trajectories indicate that the regions nearby to the Nainital and other northern Indian regions having significant BC mass concentrations during spring time. It is found that the AOD as well as BC shows significant enhancement during the biomass period (April–May). The fine mode (0.3-1.0 µm) number concentration also increases abruptly during the fire-activity period. The enhanced BC and AOD (0.5 µm) due to biomass burning are estimated to be 1.80 µgm-3 (∼145%) and 0.3 (∼150%) respectively, which leads to additional atmospheric warming of 19 W m−2 and increases the lower atmospheric heating rate by 0.8 K day−1. The AOD as well as BC at Pantnagar are quite high as compared to that at Nainital. The diurnal variation of BC at Pantnagar is entirely different than at Nainital resulting in two peaks one in morning (0700-0900 hrs) and another in evening (1700 to 2100 hrs) hours. The average BC mass concentration at Pantnagar during winter seasons is found to be ~7.9±5.2 µgm-3 which is ~44% higher than the annual mean value. BC concentration gets reduced during the spring season and an average concentration of ~4.8±3.6 µgm-3 was observed in spring. The BC mass concentration during the summer/monsoon seasons reduces to a concentration of ~2.8±2.8 µgm-3 and is ~6.5±4.9 µgm-3 in autumn. The ground based observations at both the sites have been used in radiative estimations of aerosols and other properties extensively at both the sites.


About Speaker: She has completed her 5th year in ISRO ARFI Project.



[41] Topic: Variabilities in Ozone and precursor at a high altitude site over the central Himalayas

Speaker: Tapaswini Sarangi
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-08-22
Time: 15:15hr
Venue: ARIES Auditorium

Abstract: Diurnal variations in ozone do not show a daytime build up, while, CO and NOy generally show higher levels during daytime and lower levels during nighttime at Nainital. It is shown that the diurnal variations in these gases are mainly governed by the dynamical processes including upslope downslope mountain winds and the boundary layer evolution and associated convective mixing. This is confirmed by the simulated vertical wind and the boundary layer height using WRF model. Seasonal variations in ozone, CO and NOy at Nainital are characterized by spring maxima and summer-monsoon minima. This seasonality is found in good agreement with the variability of weather parameters. Seasonality in CH4 and light (C2-C5) NMHCs shows a late autumn and early winter maxima and summer monsoon minima. This has been attributed to the post monsoon pattern along with the long range transport of pollutants during winter while regional pollution along with biomass burning activities plays key role for springtime maxima of ozone, CO and NOy. The classification based on the air-mass residence time shows ozone, CO and NOy, levels of 57±14 ppbv, 206±125 ppbv, and 1856±1596 pptv in the continental and 25±11 ppbv, 120±50 ppbv, and 336.6±211 pptv in the marine air-mass, respectively. The enhancements in ozone, CO and NOy during high fire activity period are estimated to be 4-18%, 15-76% and 35-51% respectively. Higher CO/NOy ratio during winter indicate minimal influence of local activities.


About Speaker: She has completed her 5th year in ISRO ATCTM Project.



[42] Topic: Research activities under the ABLN&C project: A part of NOBLE network under ISRO-GBP

Speaker: Raman Solanki
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-08-22
Time: 16:30hr
Venue: Auditorium

Abstract: Under the ABLN &C project a Micro Pulse LiDAR and two ultrasonic anemometers have been installed over the Manora Peak, Nainital. The site is a part of the NOBLE (Network of Observatories for Boundary Layer Experiment) network, representing a complex topographical location. Measurement of vertical distribution of aerosols and clouds over Manora peak are being made since October 2011, with a LAMP (LiDAR for Atmospheric Measurement and Probing) system. The seasonal variability in vertical distribution of aerosol has been studied over this high altitude regional representative site. Elevated aerosol layers and clouds have also been studied to understand their radiative effects on the atmosphere. In order to study the atmospheric boundary layer processes over the complex topography of the central Himalayas, a meteorological tower has been setup over Manora peak, Nainital, with Ultrasonic anemometer at two levels (12 and 27m AGL). Continuous measurements are being made since 30 January 2013. The instrument measures the wind components and temperature at sampling rate of 25Hz. Through these measurements seasonal and diurnal variability of basic meteorological parameters, momentum flux and turbulence kinetic energy have been studied. Vertical winds play an important role in mountain meteorology, as they can bring pollutants, moisture, etc. from the nearby regions, and may also bring clean air from free troposphere to the site. Seasonal and diurnal variability of vertical wind have been studied for the first time at the site. The study will be crucial in quantifying the variability in anabatic and katabatic winds over Manora peak.


About Speaker: He is JRF in ARIES, under ISRO funded ABLN&C project with Atmospheric Science Group.



[39] Topic: India’s Contribution to The Thirty Meter Telescope

Speaker: Dr. Ravinder S. Bhatia
Affiliation: TMT Associate Project Manager
Date (yyyy-mm-dd): 2013-08-12
Time: 11:00hr
Venue: ARIES Auditorium

Abstract: The Thirty Meter Telescope (TMT) represents the next generation of ground-based astronomical observatories. Driven by frontier science themes, TMT will offer 10 times the light-gathering power of the largest existing ground-based optical/near-infrared facilities, and will produce images 10 times more detailed than the Hubble Space Telescope. With this tremendous increase in power, TMT will deliver as yet unforeseen, groundbreaking discoveries about the Universe. In short, TMT will herald a new generation of telescopes and will serve its partner communities as a flagship research facility. TMT is an international partnership involving India, the USA, Canada, Japan, and China. Three main institutes constitute TMT-India: The Aryabhatta Research Institute for Observational Sciences (Nainital), the Indian Institute of Astrophysics (Bangalore) and the Inter-University Center for Astronomy and Astrophysics (Pune). The institutes are working closely with Indian industry to deliver key subsystems of the observatory, including polished segments of the main mirror, segment support assemblies, the onsite mirror re-coating facility, sensors and actuators for telescope controls, and software. These institutes also provide scientific input through their participation in the Scientific Advisory Committee. In this talk I will provide an overview of the scientific goals and technical architecture of the observatory. I will provide a status report on the construction activities, and describe the important scientific and technical contributions that are being made by India. I will also describe the challenges towards setting up the governance and management of an international partnership, and the ways in which Indian leadership is fostering an effective and collaborative working partnership.


About Speaker: Ravinder Bhatia gained his Batchelor’s degree in Aeronautics from Imperial College (1991), his Ph.D in Experimental Astrophysics and Aerospace Engineering from Queen Mary College (1998), and his Masters degree in International Relations from Cambridge University (2005). He has worked on international collaborations in technology development for over twenty years, in astronomy, Earth observation and oceanography. Previous assignments have included Project Systems Engineer for the Atacama Large Millimeter/subillimeter Array (ALMA), Senior Thermal/Cryogenics Engineer for the European Space Agency, Visiting Research Fellow at the UK National Oceanography Centre, and Senior Postdoctoral Scholar at Caltech.



[38] Topic: Analysis of Asian regional characteristics on greenhouse gaseous concentrations obtained by NIES flask sampling network

Speaker: Dr. Shohei Nomura
Affiliation: National Institute for Environmental Studies (NIES), Tsukuba, Japan
Date (yyyy-mm-dd): 2013-08-08
Time: 16:00hr
Venue: ARIES Auditorium

Abstract: This will be a short talk on the results from a networked based observations of greenshouse gases (GHGs).


About Speaker: Dr. Shohei Nomura is a scientist at NIES, Tsukuba, Japan



[34] Topic: Photometric Study of Eclipsing Binary System SS433

Speaker: Kishalay De
Affiliation: IISc, Bangalore
Date (yyyy-mm-dd): 2013-07-08
Time: 15:30hr
Venue: New Lecture Room

Abstract: Multi-wavelength photometric studies of SS 433 (also known as V1343 Aquilae) were carried out during the month of May, 2013 using the 104-cm Sampurnanand Optical Telescope at ARIES, Nainital, and their results are presented. The study aims to examine the periodicity in the obtained light curve for the object and correlate the results with previous studies. The present models for the system indicate that it is an eclipsing binary system with a B or A type supergiant and a compact object (possibly a low mass black hole) undergoing supercritical accretion from its companion star. Using data from the present photometric observations, the temperature of the secondary star appears to be around 9,000K - 11,000K, which is in agreement with typical temperatures for late B or early A type stars. Further, the radius estimated using typical luminosity values for B and A type supergiants is close to the expected radius for these stars. Using velocity data from previous spectroscopic studies and assuming an approximately circular orbit for the system, the binary separation turns out to be about 0.3 AU, with individual masses of 3.9 Msun for the compact object and 12.7 Msun for the companion star. Using Eggleton’s approximation for the radius of Roche Lobe for an object in a binary system, the secondary star appears to have filled its Roche Lobe completely. Further, using temperature extracted for the star surface, it is estimated that the radius of the accretion disk is likely to be equal to the equatorial radius of the Roche Lobe for the compact object. The circularization radius for the incoming stream of material is estimated to be around 5.7 Rsun.


About Speaker: VSP Student from IISc



[32] Topic: Dynamical Modeling and Resonance Frequency Analysis of 3.6m Optical Telescope Pier

Speaker: Pradip Gatkine
Affiliation: IIT Bombay
Date (yyyy-mm-dd): 2013-07-05
Time: 14:30hr
Venue: Auditorium

Abstract: The Pier is a very important building block of any large optical telescope. It is very evident that there are several sources of strong vibrations all around the optical telescope. A large height makes it more vulnerable to low frequency oscillations, both as surface waves, as well as bulk oscillations. These vibrations may be transferred to the optical system, which mainly happens through the pier, since it is directly connected to the telescope. In order to avoid enhanced transfer of energy between pier and optical system, it is important to ensure that the resonance frequency of the pier and the telescope fixtures are fairly separated. Hence, the as-built structure of telescope pier was modeled and simulated using FEM analysis in Solidworks Package for finding the resonating modes. Also various test procedures were defined and on-site testing was done using 3C geophones as well as Piezoelectric sensors to validate the model and to closely observe the response of the pier. The main mode in low frequency regime was found to occur at approximately 23Hz by both the testing and simulations. Thus a few parameters about the telescope were fixed. Theoretical supports are also provided for observed modes. Also, a proof of concept was demonstrated for impulse response based resonance frequency determination. It was also demonstrated that a low-cost piezoelectric sensor based test-bench can be used for finding the resonating modes, compared to expensive 3C geophones.


About Speaker: Third Year Undergraduate student Department of Mechanical Engineering IIT Bombay



[33] Topic: Constraints on Progenitors of Core-Collapse Supernovae

Speaker: RAYA DASTIDAR
Affiliation: IIT Hyderabad
Date (yyyy-mm-dd): 2013-07-05
Time: 15:00hr
Venue: Auditorium

Abstract: Observed properties of core-collapse SNe, such as light curve and spectra, are governed by the properties and environment of the progenitor star. Our objective has been to determine metallicity for a large sample of SNe at the location of explosion in their host galaxy and study the effect of metallicity on the properties of SNe types.


About Speaker: M.Sc. 1st year physics IIT Hyderabad



[16] Topic: Origin of Macrospicule and Jet in Polar Corona by A Small-scale Kinked Flux-Tube

Speaker: P. Kayshap
Affiliation: ARIES, Nainital
Date (yyyy-mm-dd): 2013-05-28
Time: 15:30hr
Venue: New Auditorium

Abstract: We report first observations of a small scale flux-tube that undergoes kinking and triggers the macrospicule and a jet on November 11, 2010 in the north polar corona. The small-scale flux-tube emerged well before the triggering of macrospicule and as the time progresses the two opposite halves of this omega shaped flux-tube bent transversely and approached towards each other. After 2 minutes, the two approaching halves of the kinked flux-tube touch each-other and internal reconnection as well as energy release takes place at the adjoining location and a macrospicule was launched which goes upto a height of ~12 Mm. Plasma starts moving horizontally as well as vertically upward along with the onset of macrospicule and thereafter converts into a large-scale jet in which the core denser material reaches upto 40 Mm with a projected speed of 95 km/s in its fast rising phase. We perform 2-D numerical simulation by considering the VAL-C initial atmospheric conditions to understand the physical scenario of the observed macrospicule and associated jet. The simulation results show that reconnection generated velocity pulse in the lower solar atmosphere steepens into slow shock and the cool plasma is driven behind it in form of macrospicule. The horizontal surface waves also appeared with the shock fronts at different heights, which most likely drove and spread the large-scale jet associated with the macrospicule.


About Speaker: P. Kayshap is working as a Senior Research Fellow at ARIES. He is pursuing the solar research on the study of trigger mechanisms of various kinds of transients and plasma dynamics in the solar atmosphere, as well as their MHD aspects to understand physical significance.



[28] Topic: Cometary dust - a probe for early solar nebula

Speaker: Prof. U. C. Joshi
Affiliation: PRL, Ahmedabad
Date (yyyy-mm-dd): 2013-05-23
Time: 15:30hr
Venue: Auditorium

Abstract: The physical and optical properties of cometary dust grains are of great interest at least for two reasons: i) these grains are responsible for much of the light scattered from cometary coma and dust tail; hence grain optics influences the basic appearances of comets; ii) the grains may be unprocessed relics from the time of formation of the solar system or before, hence study of cometary grains is very important to investigate physical conditions that exited in the beginning of the formation of solar system. This information is imprinted in the cometary dust grains. There are several ways that the cometary dust can be studied - in situ measurements using space experiments, ground based observations etc. As space based experiments are expensive and comets show differing properties, ground based studies of comets are very relevant. Photopolarimetry of the coma of comets serves as an important tool to study cometary dust. The talk will focus on a brief overview of comet study and its contribution to basic sciences. Apart from this, we have studied several comets using polarization and photometric methods. Characteristics of the cometary grains as revealed from photometric and polarimetric observations at low phase angle along with the opposition effects based on the study of comet C/2007 N3 (Lulin) by us in recent times will be discussed.


About Speaker: Prof. U. C. Joshi is a retired professor in Astronomy and Astrophysics Division of PRL, Ahmedabad. At present his is visiting faculty in the same place.



[17] Topic: Latitudinal variation of Aerosol Properties from Indo Gangetic Plains to central Himalayan foothills

Speaker: Dr U C Dumka
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-05-14
Time: 15:30hr
Venue: ARIES Lecture Hall

Abstract: Latitudinal spatial variations in aerosol optical properties are analysed over the Indo-Gangetic Plains (IGP) of northern India to a highland location in the central Himalayas during pre-monsoon (April to June) of the 2008 and 2009. Measurements of aerosol optical depth (AOD) were performed using ground based sun photometers at four sites in different aerosol environments. The AOD values increase from Kanpur (a major industrial city in central IGP) to Nainital. Further, aerosol size varies spatially with the dominance of coarse mode aerosols at Kanpur (due mainly to mineral dust transport) compared to fine mode dominated aerosols at Nainital. The spectral variation of single scattering albedo suggests the dominance of dust from IGP to Himalayan foothills (Pantnagar) during the pre-monsoon. More absorbing aerosols are retrieved at Pantnagar than Kanpur. The short wave aerosol radiative forcing (ARF) is estimated and the optical properties of aerosols (e.g. AOD, SSA, asymmetry parameter) are calculated and will be discussed.


About Speaker: ARIES



[12] Topic: Radiatively and thermally driven jets from dissipative accretion discs

Speaker: Rajiv Kumar
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-04-30
Time: 15:30hr
Venue: ARIES New Lecture room

Abstract: As the accreting matter comes close to a black hole, it may form a shock due to centrifugal barrier and may eject the rotating matter along the axis in the form of jets. And the post-shock region puffs up due to shock heating and forms a torus like structure. These post-shock hot electrons emit hard X-ray photons by inverse Comptonization of pre and post-shock soft photons. Radiations from accretion disc can accelerate the outflowing matter. We self consistently compute shock driven bipolar outflows, which are accelerated by accretion disc photons. Although we have earlier studied the issue of radiative acceleration of jets, and formation of jets from shocked accretion disc, but the two have never been connected. We vary all possible disc parameters to see how they affect the jet formation and acceleration. For some extreme parameters the jet terminal speed is found to be as high as 50% the speed of light, although, in most cases the terminal speed for such jets are around 10 to 30 % of the speed of light.


About Speaker: Rajiv is a 4th year student in ARIES. He works in theoretical astrophysics, especially on generation of bipolar jets from accretion discs.



[13] Topic: Study of Chemically Peculiar Red Giants

Speaker: Bharat Yerra
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-04-26
Time: 15:30hr
Venue: ARIES New Lecture room

Abstract: Chemically peculiar red giants, Li-rich K giants and Weak G-band (WGB) stars, are rare class of cool luminous stars whose spctra show strong Li resonance line at 6707 Ang and very weak or absent G-bands of the CH~A$^{2}Delta$ - X$^{2}Pi$ system at 4300 AA. Some of these stars are also associated with other peculiarities like: Infrared excess, rapid rotation, activity, and binarity. The origin of such anomalies in these class of stars are not well understood. To understand the underlying physical process for such anomalies, and to check the relation between their peculiarities, we have initiated a systematic study of Li-rich K giants and WGB stars. In this talk, I will discuss the properties of Li-rich K giants and WGB stars, and the results obtained from various observations.


About Speaker: Bharat is a postdoc in ARIES for the last one year, and has applied for two months extension.



[8] Topic: Oxidation capacity influenced by Convection

Speaker: Dr. Hartwig Harder
Affiliation: Max Planck Institute for Chemistry
Date (yyyy-mm-dd): 2013-03-11
Time: 15:30hr
Venue: Auditorium

Abstract: Self-cleaning processes in the atmosphere occur via oxidation processes, dominated by OH radicals. OH measurements taken in different environments, from remote marine locations, tropical and boreal forests as well as over Europe, and at different altitudes, illustrate our current understanding of HOx chemistry. While in clean air measured OH matches expectations, more polluted air, and also air with biogenic emissions, often shows enhancements of OH that indicate unknown additional processes. Convection can transport such air into higher altitudes, significantly alterating the oxidative chemistry in the upper troposphere.


About Speaker: Group Leader and group hompage http://www.mpic.de/en/research/atmospheric-chemistry/group-harder.html



[4] Topic: On the Processes Influencing the Vertical Distribution of Ozone over the central Himalayas

Speaker: Narendra Ojha
Affiliation: ARIES Nainital
Date (yyyy-mm-dd): 2013-02-19
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: Balloon-borne measurements of ozone vertical distribution and meteorological parameters are presented for a complete seasonal cycle (2011) for the first time, from a high altitude site Nainital (79.5oE, 29.4oN, 1958 m amsl) in the central Himalayas. Balloons, carrying an ozonesonde (EN-SCI 2ZV7 ECC) and a radiosonde (iMet-1-RSB 403 MHz GPS) were launched with a frequency of 3-4 flights per month which resulted in a collection of total 48 profiles during 2011. Maiden observations revealed large variabilities in the ozone distribution and meteorological parameters. Tropopause pressure is estimated to be ~100 hPa from the radiosonde observations and is in agreement with the satellite (AIRS and TES) and model (WRF) results but shows dramatic variability (150-250 hPa) during winter and early spring. Relative humidity in the lower troposphere is highest (80-100%) during summer and is attributed to the arrival of monsoon. Occasionally observed very high wind speed (~40 to 80 m/s) in middle-upper troposphere, particularly during winter, is suggested to be associated with the subtropical jets. Lower tropospheric (2-6 km amsl) ozone shows a prominent seasonality with highest levels during spring (~70-110 ppbv in May) and lowest levels during summer-monsoon (~20-50 ppbv), which is consistent with the surface observations and satellite data over this region. However, ozone seasonality is less pronounced in the middle-upper troposphere. A prominent feature of secondary ozone peaks have been observed on several occasions in the middle-upper troposphere more frequently during spring. Springtime ozone profiles are classified into high and low fire activity periods using MODIS fire counts and influence of biomass burning is estimated to be 19.9±4.6 ppbv in 2 to 4 km altitude range. Regional photochemistry is suggested to be the key process during spring with a significant contribution from the north-Indian biomass burning. Dynamical processes including advection and stratospheric intrusions play key roles except during summer-monsoon. Ozonesonde profiles with the TES operator are shown to be in good agreement with the collocated satellite (TES) retrievals. Estimated tropospheric column ozone show differences between the ozonesonde and TES during winter and is shown to be associated with the tropopause variability. These observations form invaluable datasets for the validation of satellite and model results, which is severely lacking over this region so far.


About Speaker: Mr. Narendra Ojha is Senior Research Fellow at ARIES working on distribution of Trace Gases under guidance of Dr. Manish Naja.



[2] Topic: Magnetic Field Structure around Dense Molecular Cores with Very Low Luminosity Objects .

Speaker: Ms. Archana Soam
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-02-12
Time: 15:30hr
Venue: Audotorium

Abstract: We present the results of polarization measurements of stars projected on four dense cores that are found to harbor Very Low Luminosity Objects detected by the Spitzer Space telescope. The observed dense cores are IRAM 04191+1522, L1521F, L673-7 and L1014. In IRAM 04191+1522, the separation between the magnetic field direction inferred from the optical polarization and the outflow direction is 84 degree while the separation between the magnetic field inferred from the submillimeter polarization and the outflow direction is ~ 3 degree. IRAM 04191+1522 exhibits a wind-blown morphology conspicuous in the WISE 12μm image. The direction of the maximum velocity gradient in IRAM 04191+1522 is found to be in a direction roughly perpendicular to the direction of the magnetic field inferred from the submillimeter observations. In L1521F the offset between the outflow direction and the magnetic field from our optical polarization is found to be ~ 48 degree. In L673-7 dense core, the magnetic field lines are found to be more chaotic with a slight hint of the outflow being parallel to the field towards the northern parts of the cloud. The offset between the magnetic field orientation and the outflow is found to be ~ 8 degree. In L1014, the separation between the magnetic field orientation and the outflow is found to be ~ 15 degree. The minor axis of the cloud is almost parallel to the magnetic field orientation at the periphery of the cloud.


About Speaker: Archana is ARIES 4ye student. Her Ph. D is on Polarimetry carrying under the supervision of Dr. Maheshwar Gopinathan.







[3] Topic: Star formation in Wolf-Rayet galaxy Mrk~996 : Devasthal Fast Optical Telescope observations

Speaker: Mr. Sumit Jaiswal
Affiliation: ARIES
Date (yyyy-mm-dd): 2013-02-05
Time: 15:30hr
Venue: Audotorium

Abstract: The Halpha observation of the Wolf-Rayet (WR) galaxy Mrk~996 using the newly installed 1.3 meter Devasthal Fast Optical Telescope (DFOT) are presented. Mrk~996 is a well studied galaxy, however, Ha flux and star formation rate (SFR) in the galaxy are poorly constrained by different investigators over a range of 0.2 - 3.8 ~M_sun/yr. It is classified as nE, blue compact dwarf galaxy with extremely dense gas in the core. The H-alpha analysis presented here is corrected for line contamination, Milky-way extinction, internal extinction, stellar continuum and the underlying stellar absorption. The age of the star-burst is estimated as $8 Myr. It is also noticed that the ionized gas as traced by the Ha emission is in a disk shape, which is misaligned with respect to the old stellar disk. This misalignment is indicative of a recent tidal interaction in the galaxy. We believe that the galaxy-galaxy tidal interaction is the main cause of the WR phase in Mrk~996.


About Speaker: Mr. Sumit Jaiswal work on Wolf-Ray Galaxy. He at presnt is in 4th year of his Ph.D, whic he is pursuing with Dr. A. Omar.