List of thesis/review talks


[295] Topic: Spectro-photometric study of star-forming galaxies.

Speaker: Abhishek Paswan
Affiliation: ARIES
Date(yyyy-mm-dd): 2017-12-01
Time: 15:30hr
Venue: Auditorium

Abstract: Galaxy formation and evolution is one of the most important issues in modern astrophysics. Galaxies evolve through formation of stars and their consequential effects. The evolution is also affected by several factors such as interactions or merger with other galaxies, environmental effects and feedback processes from AGN. In order to obtain a complete picture and test the theories of galaxy formation and evolution, galaxies in various stages and conditions need to be explored observationally in greater details. In this thesis, we have chosen two different samples of star-forming galaxies across the Hubble types - late-type galaxies (LTGs; spirals, irregulars and dwarfs) and early- type galaxies (ETGs; ellipticals and lenticulars), representing various evolutionary stages of galaxies over cosmic time. These samples are unique in the sense that the selected LTGs are Wolf-Rayet (WR) galaxies known to harbour very young (< 10 Myr old) star-forming regions and the selected ETGs are extremely blue galaxies with very high star formation rates (SFRs; 0.5 – 20 M_sun /yr), unlike normal ETGs which are mainly seen as quiescent galaxies. In order to understand star formation rates (SFR) and mechanisms responsible for regulating star formation, photometric and spectroscopic data for the galaxies in our samples were taken with the 1.3-m Devasthal Fast Optical Telescope (DFOT), 2-m Himalayan Chandra Telescope (HCT), Giant Meter Radio Telescope (GMRT) and archival surveys (GALEX, SDSS, IRAS and FIRST/NVSS). We constrained SFRs in galaxies and investigated that tidal interactions and/or merger of galaxies or HI clouds are most likely mechanisms for triggering star formation across all the Hubble types of galaxies. Metallicity variations within the galaxies were used to infer chemical evolution due to recent star formation and tidal interactions. In ETGs, we could estimate magnetic fields and star formation rates using radio data. Our finding supports that AGN feedback plays an important role in regulating star formation in massive starburst galaxies. On the other hand, low mass dwarf galaxies are likely to sustain a low level of star formation over long periods of time with occasional starburst, most likely triggered by tidal encounters.


About Speaker: PhD Scholar at ARIES



[268] Topic: Study of Galactic Star Forming Regions

Speaker: Ms Neha Sharma
Affiliation: ARIES
Date(yyyy-mm-dd): 2017-07-20
Time: 12:00hr
Venue: Auditorium

Abstract: The nearby isolated molecular clouds are the compelling laboratories to study the evolution of globules and the various processes of star formation. Stars can be formed in two different ways, spontaneous and triggered. In this talk, I will briefly describe the radiation-driven implosion mode of triggered star formation using three different studies. (1) Magnetic field study by polarization measurements, (2) molecular line studies, and (3) spectroscopy. Magnetic field plays a crucial role in the evolution of these molecular clouds as well as it affects the star formation processes. Hence a comprehensive study of magnetic field towards these molecular clouds is required to understand these processes. I have studied the magnetic field geometry and strength in various environments of molecular clouds e.g., cloud-cloud collision scenario, bright-rimmed clouds (BRCs), high-latitude clouds etc. Along with magnetic field study, to understand RDI processes, I will discuss the molecular line observations and subsequent results using four molecular lines towards two BRCs having different orientations of magnetic field lines with respect to the incoming ionizing radiation. To understand the effect of RDI mode of triggered star formation on the accretion properties of young stars, I have carried out optical and NIR spectroscopic observations and compared these results with non-triggered star-forming regions like Taurus. Furthermore, I will describe the research projects which I would like to continue at ARIES using the available and upcoming instruments. 


About Speaker: She has applied for PDF position at ARIES.



[266] Topic: Formation of massive stars: Observational signatures of newly evolved theories

Speaker: Dr Tapas Baug
Affiliation: TIFR
Date(yyyy-mm-dd): 2017-07-10
Time: 11:30hr
Venue: Auditorium

Abstract: Formation mechanism of massive stars (> 8 Msun) is an outstanding issue in astrophysics. It is still unknown how a massive star gains that much mass in a short time of about a Myr. This long standing puzzle about the formation of massive stars remains unresolved mainly because of their rarity, fast evolution and elusive pre-main sequence phase. Several theories have been proposed to describe the formation mechanism. Here, I shall briefly describe two theories (viz., Cloud-cloud collision and filamentary accretion) that are getting attention of the community because of their increasing observational evidences. Recently, we also found signatures supporting these two theories towards two star-forming regions, and these results will be discussed in a greater detail in my talk. Towards the end of the talk, I will briefly discuss a couple of projects carried out by me with TIRSPEC and TIRCAM2 instruments mounted on the 2-m HCT and 3.6m DOT, respectively. Finally, I shall also discuss the projects that I would like to pursue at ARIES using the available observing facilities.


About Speaker: Dr. Tapas Baug has applied for the PDF position at ARIES.



[248] Topic: Evolution of magnetic activities in late-type stars

Speaker: Mr. Subhajeet Karmakar
Affiliation: ARIES
Date(yyyy-mm-dd): 2017-03-31
Time: 10:15hr
Venue: Auditorium

Abstract: Cool stars with convective outer envelope show similar-type of magnetic activities to that of the Sun hence have a similar type of dynamo. Although, the observations of these stars have introduced a range of stellar rotation periods, gravities, masses, and ages, which put into the debate on the magnetic dynamo. The important observational evidences of these magnetic activities are the presence of dark spots on the surface, short- and long-term variations in spot-cycles, and flares. In this thesis, we have chosen five active stars with luminosity class V to III to investigate the evolution of magnetic activities. These active stars are LO Peg, 47 Cas, AB Dor, CC Eri and SZ Psc. Using ~24 yrs long multi-band data, we found that the surface of LO Peg rotates differentially showing solar-like SDR pattern with a period of ~2.7 yr. The surface coverage of cool spots is found to be in the range of ~9--26 % in LO Peg. Several moderate-sized flares and two superflares on active dwarfs 47 Cas, AB Dor, and CC Eri are also analyzed. A large flare on evolved RS CVn type stars was also observed and analyzed. The time-resolved spectral analysis during these flares shows the variation in the coronal temperature, emission measure, and abundances. The peak temperatures in these moderate flares are found to be in the range 10--90 MK, whereas the peak flare temperatures in superflares are found to be mode than 120 MK. In most flares, during the decay, a sustained heating was detected. Using the hydrodynamic loop modeling, we derive loop-lengths of the flares of the order of 10^10 cm. In nutshell, we found that the magnetic activities in these star changes with time.


About Speaker: Mr. Subhajeet Karmakar is a research scholar and pursuing PhD under supervision of Dr Jeewan Pandey. This is his PhD submission presentation.



[244] Topic: Study of Galactic Star Forming Regions and Related Instrumentation

Speaker: Neha Sharma
Affiliation: ARIES
Date(yyyy-mm-dd): 2017-01-20
Time: 15:00hr
Venue: ARIES Auditorium

Abstract: The nearby isolated molecular clouds are the compelling laboratories to study the evolution of globules and the various processes of star formation. Magnetic field plays a crucial role in the evolution of these molecular clouds as well as it affects the star formation processes. Hence a comprehensive study of magnetic field towards these molecular clouds is required to understand these processes. In this thesis, we have studied the magnetic field geometry and strength in various environments of molecular clouds e.g., cloud-cloud collision scenario, bright-rimmed clouds (BRCs), high-latitude clouds etc. When unpolarized starlight passes through the intervening interstellar dust grains that are aligned with their short-axis parallel to the local magnetic field, it gets linearly polarized. The plane-of-the-sky magnetic field component can, therefore, be traced by doing linear polarization measurements of background stars projected on the clouds. We have chosen the regions to map magnetic field geometry on the basis of two different classifications of star formation, triggered and spontaneous. Triggered star forming regions e.g. cometary globules, bright-rimmed clouds are mainly associated with HII regions having a high mass star in the center of it. When massive star forms it photoionizes the surroundings, forming HII regions, that display highly irregular structures such as filaments, pillars, CGs and BRCs. In the radiation-driven implosion (RDI) mode of triggered star formation, the incoming ionizing radiation from that massive star further compresses these small clouds to collapse and make them gravitational unstable to form new stars. We have chosen a HII region Sh2-262 having multiple BRCs to map the magnetic field geometry and strength. On the basis of magnetic field lines orientation in these BRCs we compared our result with the MHD simulations and studied the RDI mode of triggered star formation. More so, we compared these results with the previously studied HII regions, Sh2-131, Sh2-185, Sh2-236 and Sh2-126. Along with magnetic field study, to understand RDI processes, we performed molecular line observations using four lines in two BRCs having different orientations of magnetic field lines with respect to the incoming ionizing radiation. We carried out optical and NIR spectroscopic observations to estimate the mass accretion rates in young stellar objects associated with triggered star forming regions and compared them with non-triggered star-forming regions like Taurus. Furthermore, we made an optical design of Wide-field polarimeter (Wi-Fi Pol) for 1.3m Devasthal Optical telescope and developed a polarimetric data reduction pipeline.


About Speaker: Ms Neha Sharma is research scholar at ARIES and working in the field of Astronomy for her PhD under supervision of Dr Maheswar Gopinathan. This is her thesis Pre-submission talk.



[239] Topic: Multi-band Studies of Blazars with XMM-Newton

Speaker: Nibedita Kalita
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-09-30
Time: 15:30hr
Venue: Auditorium

Abstract: Blazars are sub-class of the radio-loud Active Galactic Nuclei (AGN), which emits highly luminous, polarized and non-thermal radiation covering the entire electromagnetic spectrum from a highly compact center (i.e., SMBH). The blazars with higher luminosity and jet angle are known as FSRQs (Flat spectrum radio quasars), while the BL Lac objects show comparatively low luminosity and smaller jet angle (in both cases the jet angle is < 10 degree). Moreover, the SED synchrotron peak of FSRQs lies in the radio to optical range but for BL Lacs the synchrotron hump peaks in UV/X-rays. One of the most interesting phenomenon that blazars show is the multi-frequency flux variation on diverse timescales. The aim of this thesis is to explore the twisted emission mechanisms involved in the local environment of the SMBH that resides at the center of blazars and to study variability properties in multi-wavelength scenario. We have undertaken two different approach to understand the blazar emission; (1) temporal study in multi-frequency domain and (2) X-ray spectral study. The work presented in this thesis is based on the observations made by XMM-Newton observatory. As part of the first approach, we have studied variability on Intraday & Long (years) timescales and correlated variability between optical, UV & X-ray bands for the FSRQ 3C 273 and found that two electron populations with different Lorentz factors are involved in low and high energy emissions. A hardness ratio analysis in the X-ray regime indicates that the particle acceleration mechanism dominates the cooling mechanism during most of the time. An extensive study with possible correlations, variability timescales and QPOs in a sample of ISP blazars in their outburst state, with the most efficient techniques like SF, ACF, DCF & PSD to understand the complex emission from the relativistic jet and the jet structure has also carried out. We have studied the relation between synchrotron peak of multi-band SED and the X-ray IDV for a sample of a dozen of blazars (includes 10 LSPs and 2 ISPs). Here we have concluded that the highest energy electron available for syncrotron emission will have retarded effect on X-ray IDV. X-ray spectral study of the border line blazar 3C 273 in the energy range 2.5-10 keV, from 2000 through 2015 revealed some new information about the source. A new minimum flux state of 3C 273, even lower than the historical minimum during 2003-2004, was observed in 2015. A harder-when-brighter trend is observed in these long-term multi-epoch observations of 3C 273 for the first time. With simultaneous study of the X-ray continuum and ultraviolet emissions during the quiescent state of the source, we have detect a significant anti-correlation between the X-ray spectral slope and the X-ray to UV flux ratio. From this detection we conclude that the 2.5-10 keV X-ray emission is the result of IC scattering of soft UV seed photons in a thermal corona based above the accretion disc.


About Speaker: Nibedita Kalita is a 5th year PhD student working with Dr Alok Gupta. This is her Pre PhD submission talk.



[231] Topic: Study of Aerosol Distribution and associated Meteorology over the central Himalayas

Speaker: Raman Solanki
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-08-12
Time: 15:30hr
Venue: Auditorium

Abstract: Air pollution is intrinsically linked with meteorological parameters and this linkage further strengthens over complex mountainous terrain, an attempt to understand this association over a mountain ridge in the central Himalayas through measurements of aerosol vertical distribution, surface layer characteristics and local boundary layer (LBL) evolution is being made. This study presents ground based measurements taken at ARIES, Nainital (Manora Peak, 79.5oE, 29.4oN and 1958 m AMSL) over a period of October 2011 to February 2014. Intermittent LiDAR observations were made during March 2012 to May 2013 out of which 57 suitable cases have been subjected to analysis. A comparison of ground based LiDAR observations with the CALIPSO satellite derived aerosol backscatter profiles has been carried out for 37 suitable cases. The mean percent bias for different seasons are found to be +18±42%, +22±28%, +32±36% and +18±51% for MAMJ-2012, SON-2012, DJF-2012-13 and MAM-2013 respectively. Surface layer characteristics have been studied during spring (2013) and winter (2013-14) season, utilizing the 3-D wind components and virtual temperature observed with sonic anemometers (sampling at 25 Hz) mounted at 12-m and 27-m height on a meteorological tower. A new criterion of SNR > 6 dB for the LBL characterization has been implemented; the resulting estimations are found to be in agreement with radiosonde measurements over the site. The daytime average observed LBL height ranges from 440±197 m in November (late autumn) to 766±317 m 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 height of 650 m during nighttime. The RWP measurements of LBL are further utilized to evaluate biases in model simulated boundary layer and the implications of these biases in context with trace species model simulations.


About Speaker: Raman Solanki is pursuing his PhD from ARIES Under the supervision of Dr Narendra Singh, and he is registered with University of Delhi.( It is a pre-submission Seminar)



[229] Topic: Study of ozone and precursors over the Himalayan region

Speaker: Mr Piyush Bhardwaj
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-08-04
Time: 15:30hr
Venue: Auditorium

Abstract: Ozone and related trace gases (CO, NOx, VOCs, etc.) play essential roles in determining air quality, oxidizing capacity of the atmosphere, budgets of various other trace gases and also climate change. The emissions of these gases are increasing over Indian subcontinent owing to rapid growth in economy and higher energy needs. Further, satellite retrievals also indicate high levels of pollution across Indo-Gangetic plain and this pollution under favorable meteorological conditions can be transported to other regions as well, including the pristine Himalayas. In light of above facts, an extensive study performed during a PhD thesis was aimed to understand some of the underlying processes and to fill the gaps through surface based observations of ozone and related trace gases over the Himalayan region during SusKat field campaign and balloon borne observations of ozone and met parameters over Manora Peak, Nainital. During the SusKat observations, it was realized that the discrepancies between the model and observation results could be mainly due coarse resolution of input emission inventories. Additionally, further tuning in the model setup, including testing of various land surface models etc are needed. The use of a chemical box model could also provide in-depth information on the underlying atmospheric chemistry of the region. Here, I propose to setup and use the box-models, improvement in WRF-Chem setup over the Himalayan region, improvement in emission inventories. Some campaign based specific vertical measurements of ozone and meteorological parameters could be carried-out during my PDF tenure at ARIES to investigate above mentioned objectives.


About Speaker: Mr Piyush Bhardwaj has applied for the PDF position at ARIES.



[215] Topic: Studies of Nearby Star Forming Galaxies

Speaker: Sumit Jaiswal
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-30
Time: 15:30hr
Venue: Aries Auditorium

Abstract: Star formation plays a major role in galaxy evolution and its energetics over cosmic time. We have selected a sample of 26 Wolf-Rayet (WR) galaxies to study the star formation scenario in galaxies. The galaxy-galaxy tidal interaction is expected to be fundamental mechanism which triggers star formation in galaxies. We have performed HI 21-cm line and H-alpha line imaging of these galaxies to see the interaction features in the selected galaxies. The H-alpha observations together with archival data from various surveys provide very important correlations between star formation rates estimated using different radiation mechanisms. The radio-FIR correlation in WR galaxies is also estimated.


About Speaker: Ph.D. Student



[212] Topic: On the nature of radio-quiet weak emission line quasars.

Speaker: Parveen Kumar
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-17
Time: 15:45hr
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 unrecognised 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. For this we carried out spectral and polarisation measurements of a sample of 19 such RQWLQs. Out of them only 9 sources show non-significant proper motion, and all of them show percentage polarisation (P) less than 1%, except two sources J142505.59+035336.2 and J154515.77+003235.2 with highest polarization 1.59 ± 0.53%. This small percentage polarisation of RQWLQs seems too low for them to be the radio-quite analogue of Bl-lac objects. We also report a statistical comparative study of the spectral slope, temporal variation of the continuum flux at different time scales using a sample of 45 RQWLQs with 900 redshift-luminosity matched control sample of QSOs and 120 blazar collected from the literature. The structure function analysis shows that the mechanism triggering the optical variability in RQWLQs seems similar to that in QSOs and unlike blazar which are generally highly variable at all time scales. Similarly, the spectral slop distribution of RQWLQs differ at high significance from that of blazars, suggesting that the mechanism of RQWLQs central engine might be resembling more with that of normal QSOs, perhaps with less developed BLR as a cause of their weak emission lines; unlike the Bl-lac/blazar objects whose continuum emission are dominated mainly by their relativistic jet. The paper has been written and submission is expected in next two three weeks.


About Speaker: Mr. Parveen Kumar is a 4th year student working with Dr. Hum Chand



[213] Topic: High resolution simulation of CO2 transport by a regional model WRF-CO2 over South Asian region

Speaker: Srabanti Ballav
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-17
Time: 14:30hr
Venue: Auditorium

Abstract: The increase of atmospheric CO2 concentration due to anthropogenic activities and hence induced climate change has captured the attention and concern of human society. In this regard, the high resolution forward transport model simulations of CO2 at hourly to synoptic timescales have attracted considerable interest in recent time. This becomes important for predicting the future climate to a high degree of certainty. Extensive studies using high resolution CO2 forward transport models are carried out over the United State, Europe and East Asia. However, such studies are very few over South Asia. In view of this, a high resolution regional forward transport model, Weather Research Forecast model for CO2 (WRF-CO2) is being setup for South Asia to better understand the spatial and temporal CO2 variations over this region. Here, a fully coupled, online, regional air quality model WRF-CO2 has been setup and used for the first time to simulate long term CO2 over South Asian region. Comparison of the model results with the ground–based measurements indicates that the model reproduces the spatial and temporal variation of CO2 concentration with higher bias during the growing season. Model results from WRF-CO2 are able to resolve fine scale structures and are facilitating interpretation of CO2 observations. The WRF-CO2 model was able to reproduce the diurnal pattern of CO2 concentration for two observation stations but amplitude of diurnal cycle of CO2 is not captured by the model, particularly over growing season.


About Speaker: She is a Post-Doctoral Fellow at ARIES and this is her first year review talk.



[210] Topic: On the INOV Properties of X-ray Bright NLSy1 Galaxies and Photometric Reverberation Mapping of AGN.

Speaker: Mr. Vineet Ojha
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-16
Time: 15:45hr
Venue: Auditorium

Abstract: Broadly my research work would be based on the “Multi-wavelength study of Active galactic Nuclei(AGN)”. This year I have mainly focused on a class of AGN called Narrow line Seyfert 1 (NLSy1) galaxy. The sample consist of well selected 18 NLSy1 galaxies, which are at least detected in X-ray at more than 3σ level. The aim to choose X-ray bright NLSy1 is to explore the origin of X-ray emission since generally Seyfert galaxies are less prominent in high energy band. The other motivation was the recent surprising discovery of gamma-ray emission from dozen of NLSy1 galaxies, which has been associated to the presence of jets in their center, generally found in elliptical radio galaxies/rather than in spiral galaxies. So one possibility is that may be the cause of X-ray emission in X-ray detected NLSy1 galaxies might also be associated to the mild jet activity in their center, as proposed gamma-ray detected NLSy1 galaxies. Higher duty cycle of Intra-night optical variability is one of the diagnostic commonly used to quantify significant jet activity where even small fluctuation in flux can get Doppler boosted. Therefore we have used the ARIES 1.3m DFOT telescope for the INOV study of our sample. As of now about 16 sources have been monitored each lasting for more than 3.5 hours. The data has been analyzed and paper is almost in final stage. Out of the total 16 session we have not found any source which show variability after applying robust statistical tests. This suggests the absence of jet dominance as for as X-ray emission is concerned, though our source being faint the improvement required higher sensitivity using 2m class telescopes. Our group is also involved in making the catalog of NLSy1 galaxy based on large data-set of 1.5 million AGN from SDSS-DR12, which I plan to use to prepare a sub-sample for their multi-wavelength study especially with ARIES 3.6m DOT for optical and astro-sat for X-rays for detail study in my thesis. In addition, I was also a part of photometric reverberation campaign carried on 15 night from 1.3m telescope. My involvement was assisting the observation and then reduction of the data in two broad and one narrow band, which has been also completed. This program is to characterize the L-R relation of broad line region of low luminosity AGN.


About Speaker: Mr. Vineet is a 2nd year student working with Dr. Hum Chand.



[211] Topic: Study of cool gas outflows from AGNs

Speaker: Ms. Sapna Mishra
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-16
Time: 14:30hr
Venue: Auditorium

Abstract: This year I have focused on cool outflows associated with class of AGN known as Blazars. It is believed that the cool gas clouds (eg.MgII absorption system) with velocities βc ≤ 5000 km/s relative to the background quasars are associated to quasar itself (associated system) however absorber with velocity offset beyond this limit are ‘intervening system’ and their presence is completely independent of background quasar. Recent evidence, however, appears to question this canonical view and suggests that even associated systems can have significantly relativistic velocities relative to the background quasar, in case the quasar is undergoing powerful jet activity and/or ejecting high speed accretion-disk outflows (Bergeron et al.2011). A possible signature of this would be if the occurrence rate, dN/dz, of ‘intervening’ absorbers is found to differ for background sources with and without powerful jets. The reason behind this departure is attributed to the powerful jets activities along the line of sight of observer which are responsible for an excess in value of dN/dz and hence are the main source of intrinsic cool outflows. With this motivation whether or not the existence of excess cool absorbers is related to background source we have used a sample of 97 Blazars with 0.5


About Speaker: Ms. Sapna is a 2nd year student working with Dr. Hum Chand.



[207] Topic: Optical Study of Core Collapse Supernovae and their progenitor environment.

Speaker: Raya Dastidar
Affiliation: Aries
Date(yyyy-mm-dd): 2016-06-15
Time: 15:45hr
Venue: Auditorium

Abstract: Observed properties of core-collapse supernovae (ccSNe), such as light curve and spectra are governed by the properties and environment of the progenitor star. Stripped envelope supernovae, a subclass of ccSNe, takes under its wings type Ib, Ic and IIb SNe. As the name aptly suggests, the progenitor star is stripped of its envelope prior to explosion. The extent of stripping depends on the environment of the star and/or the presence of a massive binary companion. We present in this report the broad band BVRI investigations of SN 2012P in the galaxy NGC 5806 obtained during 2012 Jan 24 to Jun 27. A photometric follow up was initiated within 2 days after the discovery (Jan 22), but due to the late discovery of the event the peak was not covered. We used χ2 minimization technique to determine the explosion epoch by fitting the SN 1993J light curve to our light curve. This suggested a probable explosion epoch which is 16 days prior to its discovery. Hence, we adopted 2012 Jan 6 as the possible explosion epoch. Further, we eliminated the host galaxy contamination underlying the SN position using High Order Transform of Psf And Template Subtraction software with template images acquired on 2013 April 14, almost a year later. It is found that the light curve of SN 2012P obtained from the difference images closely resembles SN 1993J, a prototype of this subclass, during the first∼50 days, but the event SN 2012P is considerably fainter than other well studied type IIb events.


About Speaker: Ms. Raya Dastidar is a 2nd year student working with Dr.Brijesh Kumar



[208] Topic: Bright Rimmed Cloud: A Potential Site of Triggered Star Formation

Speaker: Piyali Saha
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-15
Time: 14:30hr
Venue: Auditorium

Abstract: Bright Rimmed clouds (BRCs) are small molecular clouds located at the periphery of evolved HII regions with their 'bright rims' facing towards ionising star(s) side. They are believed to be the potential sites of triggered star formation due to the pressure exerted by the incoming ionising radiation from the massive ionising star(s). Thus, they are good examples of the radiation driven implosion (RDI) mode of triggered star formation. But, star formation frequency, star formation efficiency and stellar mass function due to RDI are still unknown. Details of RDI mode can be acquired by observing a number of BRCs that are classified as triggered and non-triggered based on previous studies. For this purpose, pilot study has been done on two BRCs, namely SFO 18 and SFO 38 which are considered as non-triggered and triggered respectively. We have mapped thsese BRCs with 12CO, C18O, N2H+ and HCN (J=1- 0 transition) lines to understand the dynamics, excitation temperature, column density and optical depth traced by these lines. By using continuum emissions in far-infrared region we have estimated dust temperature, spectral emissivity index and other physical parameters of the dust present in these two BRCs. Priliminary results will be discussed in my talk.


About Speaker: Ms. Piyali Saha is a 2nd year student working with Dr. Maheswar G.



[198] Topic: Probing physical properties of dark molecular cloud L1157

Speaker: Ekta Sharma
Affiliation: Aries
Date(yyyy-mm-dd): 2016-06-14
Time: 14:30hr
Venue: Auditorium

Abstract: In order to understand the whole process of star formation, it is important to have a comprehensive understanding of the evolution of dense cores. The low mass star-forming regions are ideal labo- ratories for such studies because low mass young stars evolve much more slowly and the sample of low mass stars is also relatively large as compared to high mass stars. Therefore, the complete knowledge about different physical properties of the cloud can be extracted out using different observations. Here, the L1157 dark molecular cloud has been studied. The work is being reported into two parts: 1) Magnetic field studies in the dark cloud using optical polarimetry and 2) Molec- ular line studies using radio observations of CO, C18 O, N2H+, HCN molecules. The plane-of-the sky component of the magnetic field is obtained from polarization maps and different parameters from these spectral lines data is calculated. This will help in charaterising about the different evolutionary stages of the cloud that will eventually give rise to star formation.


About Speaker: Mrs.Ekta sharma is a 2nd year student working with Dr. Maheswar G



[206] Topic: REVIEW REPORT (Second year) Broad-band photometric survey of zenith sky at Nainital

Speaker: Pankaj
Affiliation: Aries
Date(yyyy-mm-dd): 2016-06-14
Time: 15:45hr
Venue: Auditorium

Abstract: We present the scheme and preliminary results of a broadband photometric survey of zenith sky at latitude (29.4 deg) of Nainital. The aim of the survey is to generate fainter standard stars in the 30 arcmin strip of the zenith sky. This data can be used for a wide vari- ety of astronomical topics as well as technical characterization of telescope and instruments. This limited zenith sky survey is being done at broad-band U,B,V,R and I lters using 1kХ1k CCD mounted with the 104-cm telescope, the work involves observation-calibration of the photometric images.


About Speaker: Mr. Pankaj is a 2nd year student working with Dr. Brijesh Kumar



[205] Topic: Optical Studies Of Stripped Envelope Supernova

Speaker: Anjasha Gangopadhyay
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-13
Time: 14:30hr
Venue: Auditorium

Abstract: Context We present the optical studies (ugriz, BVRI) of a type IIb supernova SN2015as. Super- novae(SNe) IIb show a variety both in light curve and spectral features. An analysis of this has been done. Data has been taken from 104-cm Sampurnanand Telescope, 130-cm Dev- asthal Fast Optical Telescope (DFOT), 200-cm Himalayan Chandra Telescope and 182-cm Asiago Ekar Telescope. Four epochs of UV data has also been taken with Swift UVOT. Aim We study the optical light curve evolution of a Type IIb supernova (SN) 2015as starting from 1 to 150 day after discovery and the spectral evolution of this SN at two epochs. We also present the apparent, absolute magnitude light curve and colour curve of SN2015as. Method Raw data(Optical) taken from different telescopes was first preprocessed using IRAF soft- ware. Basic photometric reductions has been done using the DAOPHOT package. Results and Discussion Although the peak of the BVRI lightcurve could not be covered since the first observation was taken after 17days from discovery, but the ugriz evolution was studied from 2 days after discovery. We fit a spline function to r and i bands to estimate peak magnitude and time. The r and i band light curves peaked around 22 and 27 days respectively after explosion with a peak magnitude of 14.26 and 14.96 respectively. The extinction corrected (V-I) and (R-I) light curves show that the SN 2015as is much bluer than other SN of this group. Also, the absolute magnitude curve for the V band shows that the absolute magnitude is much less as compared to other members of this group and peaks around -17 mag. From the spectral evolution, we see that the +19 day spectrum of SN2015as showed broad P-cygni absorption of Hα (λ6563Å) and absorption due to Hβ, Hγ and Ca II H and K. The spectra around 19 days also shows He features at λ5876Å. This marks the property of type IIb SN that shows transition from initial H to He features. Also, in late time spectra red region shows OI and Mg II lines.


About Speaker: Ms. Anjasha Gangopadhyay is a 2nd year student working with Dr. Kuntal Mishra



[202] Topic: Flare, Surge Eruption and the evolution of Photospheric Doppler enhancements

Speaker: Aabha Monga
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-07
Time: 14:30hr
Venue: Auditorium

Abstract: In this review, I am going to present the multi-wavelength analysis of C6.1/SF are occurred on June 12, 2010 from active region NOAA AR 1081 with the complexity of βγ and was associated with Type II radio burst and Coronal Mass Ejection (CME). We have used ARIES Hα data, SDO- AIA/HMI, SoHO-LASCO and STEREO/SECHHI data for this study. The are is accompanied by surge like ejection and later produce Type II radio burst with a slow CME( 382 Kms/sec) and initially CME speed was high ( 700 Kms/sec). Here we report the co-spatial evolution of the Doppler enhancements and the chromospheric Hα ribbons observed during X1.2 Class are observed on May 15, 2013. The velocity enhancements exactly match the Hα brightness enhancements with the delay of approximate 2 minutes delay.


About Speaker: Mrs. Aabha Monga is a 4th year student working with Dr. Wahab Uddin.



[201] Topic: Multi-Wavelength study of Magnetic CVs

Speaker: Arti Joshi
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-07
Time: 15:45hr
Venue: Auditorium

Abstract: We present analyses of archival X-ray data obtained from the XMM-Newton satellite of an intermediate polar V2400 Oph. The X-ray variations occur at the 1003-s synodic period which is strongly indicated in the power spectrum of the time series. The blackbody temperature of irradiated poles of the white dwarf atmosphere is found to be 90 eV, much higher than those found in their synchronous analogues, the Polars. The EPIC-PN spectra shows the presence of soft X-ray components. Blackbody-like emission, similar to that seen in soft IPs - however through higher absorption, probably arises from the white dwarf surface. The temperature of the optically thin postshock plasma is well constrained 13 keV, being strongly absorbed by dense material with an equivalent hydrogen column density of 8.2×1022 cm -2, which partially cover 36±2 % of the Xray source together with Fe Kα emission line. The new observations support V2400 Oph to be a discless accreting system. We also present the phase-resolved spectroscopy in 0.1-10.0 keV energy range and found that spectral parameters are phase dependent. Photometric and Polarimetric observations of eighteen unidentified magnetic CVs were also carried out in 130 nights from 1-m class telescopes of ARIES, Nainital. Among all these CVs we also present optical results of the four candidates IPHASJ013+622, IPHASJ025+635, IPHASJ034+533 and IPHASJ051+294. Three of the systems IPHASJ013+622, IPHASJ025+635 and IPHASJ051+294 were found to be eclipsing from photometric data. Orbital periods of these CVs lie above the period gap of 2-3 h, which indicates that these can be classified as an intermediate polars.


About Speaker: Ms. Arti Joshi is a 4th year student working with Dr. J. C. Pandey.



[200] Topic: Investigating the Behaviour of Exploding Stars

Speaker: Mridweeka Singh
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-06
Time: 14:30hr
Venue: Auditorium

Abstract: Supernovae are the dominant sources of stellar feedback, which plays an important role in regulating galaxy formation and evolution. During the previous five observing seasons from October 2014 to April 2016 we observed a number of events covering various subtypes of SNe such as Ia, Ia-pec, Ib and IIP starting from nearly 10 days after discovery and lasting upto approximately 200 days. Amongst these we present photometric and spectroscopic evolution of a type Ia-pec event SN 2014dt in M61. We present the light curve studies, evolution of colors and compare the luminosity of SN 2014dt with other peculiar events of Ia class. The spectra of SN 2014dt at 22d and 67d after explosion is compared with SN 2005hk at similar epochs.


About Speaker: Ms. Mridweeka Singh is a 3rd year student working with Dr. Kuntal Mishra.



[189] Topic: Study of the Tropospheric trace gases over the Indian subcontinent

Speaker: Piyush Bhardwaj
Affiliation: ARIES
Date(yyyy-mm-dd): 2016-06-01
Time: 14:30hr
Venue: Auditorium

Abstract: The Indian subcontinent is among the most populated and highly polluted regions in the world and emissions are increasing over this region due to rapid economic growth here. These increasing emissions have strong implications not only for the large population residing in this region but it can also reach other parts of the world via long range transport. This region is among the least studied parts of the world and limited observations hampers the better understanding of the changing atmospheric chemistry over the region. This thesis describes results from two field campaigns viz., SusKat and GVAX over the Himalayan region; satellite based study of biomass burning over the Indian subcontinent, and balloon borne measurements of ozone and meteorological parameters over ARIES, Manora Peak. The seasonal and interannual distribution of biomass burning activity (2003-2013) indicated distinct seasonal cycle over this region and show that the fire activity has increased during last five years (2008-2013). Large differences were observed in the budgets of trace species emitted during these fires. The emissions show biannual peaks in spring (Mar-May) and autumn (Sep-Nov) season with higher emissions in the later season. For the first time, a field campaign for the measurement of trace species was conducted in Kathmandu Valley, Nepal during Jan-Jun 2013. The ozone and CO levels at Bode, Nepal in the valley were found to be higher than Pantnagar, India. The regional scale pollution from IGP is suggested to contribute to the higher levels during an event in spring season. For the first time high resolution WRF-Chem model setup was done over the Himalayan region and model is able to capture variations in temperature, RH and winds. Model also showed good agreement in daytime levels of CO however, ozone and NOx were over and underestimated. The long term change in the vertical distribution of ozone was studied using balloon borne measurements at ARIES, Manora Peak. The contribution of spring time biomass burning to the ozone levels in lower troposphere is also estimated. Results obtained using the high frequency balloon-borne measurements of meteorological parameters during Ganga Valley Aerosols experiment (GVAX) at ARIES, Nainital indicated high wind speed (~85 m/s) near the subtropical jet. The observations also showed better agreement of wind speeds at 250 hPa (altitude of subtropical jet) than other levels with reanalysis datasets The Satellite based retrievals indicated negative bias in temperature profiles in the lower altitude region, and positive bias near the tropopause. WRF simulated results are able to capture variations in temperature, humidity and wind speed profile reasonable well. The detailed results will be discussed during the talk.


About Speaker: Mr Piyush Bhardwaj is a Research Scholar in atmospheric science group and pursuing PhD with Manish Naja. This is a presentation related with his pre PhD thesis submission.



[171] Topic: Multi-wavelength Studies of Active Galactic Nuclei

Speaker: Jai Bhagwan
Affiliation: ARIES, MANORA PEAK, NAINITAL
Date(yyyy-mm-dd): 2016-03-04
Time: 15:30hr
Venue: ARIES Auditorium

Abstract: Active Galactic Nuclei (AGN), refers to the existence of energetic phenomena in the nuclei, or central regions, of galaxies which can not be attributed to stars. AGN has a super-massive black hole at its center which accretes matter. Two major classes of AGNs are radio-quiet and radio-loud AGN. In my Ph.D. thesis, I have worked on a sub-class of radio-loud AGN called blazars. The blazars, I selected for my studies are TeV emitting blazars and known as TeV blazars. Blazars emit radiation in the complete EM spectrum. Their flux and polarization are highly variable on all diverse timescales and emission is predominately nonthermal. My thesis results has 2 parts: (1) Multi-wavelength (optical/UV, and X-ray) observations of the TeV blazar PKS 2155 - 304 with XMM-Newton, (2) Multi-band optical observations of 3 TeV blazars; on diverse timescales. (1) Using ~ 12 years XMM-Newton archival simultaneous data in optical/UV and X-ray bands of PKS 2155 - 304, we studied flux and spectral variability on diverse timescales and have tried to model the spectral energy distribution (SED). In a specific observation, we noticed the evidence of particle acceleration and synchrotron cooling both are at work for the first time. We also estimated the various parameters of SEDs. (2) In multi-band optical studies of 3 TeV blazars, we have made new observations using 5 telescopes (2 in ARIES, 1 in Bulgaria, 1 in Greece, and 1 in Serbia). We have studied flux and color variations in these 3 TeV blazars on diverse timescales as short i.e. few tens of minutes and as long i.e. few years. We discuss the possible physical mechanisms most likely responsible for the observed flux variability.


About Speaker: Mr. Jai Bhagwan joined ARIES as a Ph.D. student in August 2010 and after completing one year of pre-Ph.D. course work he joined his research project in supervision of Dr. Alok C. Gupta. In December 2013, he joined PG Teacher, Physics job in a Government college in Rohtak, Haryana. His Ph.D. work is completed and he will be submitting his Ph.D. thesis in Raipur University on next week.



[161] Topic: A Study on dynamical Aspects of aerosol over the central Himalayan region

Speaker: Krishna Kumar Shukla
Affiliation: ARIES
Date(yyyy-mm-dd): 2015-11-30
Time: 15:30hr
Venue: Auditorium

Abstract: To study the dynamical aspects of aerosols, we have utilized continuous and simultaneous datasets performed during an Indo-US collaborative project the Ganges valley aerosols experiment (GVAX) during June 2011-March 2012 over a high altitude site Manora Peak, Nainital in the central Himalayan region due to its unique topography. A detailed discussion about the dynamics and estimation of diurnal/seasonal variation of ABL height by using different methods have been done in this thesis and found that it varies between ~ 0.6-1 km, above ground level (AGL) in all the seasons. The estimation of ABL cloud base height (CBH) by using Doppler Lidar and ceilometer have been done and found good correlation R2=0.76 between both the CBH. We have studied the diurnal/seasonal variation of vertical velocity (VV) (it shows the upslope and downslope wind during daytime and nighttime respectively over the site) and VV variance (it shows the intensity of turbulence over the site). We have also observed that the aerosol optical depth is modulated with the periodicity of ~ 60-80 min (gravity wave) and with period of ~ 25-45 (Rossby wave) days dominant over the observational site. We have observed an additional atmospheric warming due to waves (Gravity and Rossby) of ~ 40 and 16 % respectively.


About Speaker: Mr. Krishna Kumar Shukla is Research Scholar in Atmospheric Science group and pursuing his PhD with Dr. D V Phani Kumar. This is a PhD pre-submission talk.



[141] Topic: Multiwavelength investigation of Core-Collapse supernovae

Speaker: Mr Subhash Bose
Affiliation: ARIES
Date(yyyy-mm-dd): 2015-08-17
Time: 15:30hr
Venue: Auditorium

Abstract: Supernovae (SNe) are one of the most energetic cosmic events in the universe and they are prime candidates responsible for heavy element enrichment in present universe. The study of these exotic events are fascinating in itself. Core-Collapse supernovae (CCSNe) are the end fate of massive stars with wide range of properties and so the observable parameters of these explosions are also very diverse. Circumstellar environment and history of pre-SN evolution also plays a key role in diversifying their properties. In this thesis we characterize a number of CCSNe events which has been extensively observed in photometric, spectroscopic and polarimetric modes at optical wavelengths. This thesis utilizes data collected primarily from telescopes in India viz. 104cm ST and 130cm DFOT at ARIES, 2mIGO at IUCAA and 2mHCT at IIA. Complementary data were also collected from several international network of telescopes and Swift UVOT observations. 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 characterize five CCSNe events (SNe 2012aw, 2013ab, 2013ej, 2013hj and 2014G) in detail. Along with the determination of various physical parameters by modeling the observables, we also probe peculiarities which they exhibit in their observed light curves and spectra. Our detailed observations and spectroscopic modelling revealed ejecta-CSM interaction in SNe 2012aw and 2013ej, and also signature of emergence of recombination phase for the first time in SNe II. Such detections are crucial to improve our understanding of these event. Another vital component of this thesis is utilizing type II SNe as a distance estimator, which has immense cosmological as well as astronomical importance. SNe due to high intrinsic brightness are always an attractive probe for extragalactic distance measurements, however SNe II require an approach which is entirely different than standard candle methods. We implement Expanding photosphere method (EPM) to estimate distances to host galaxies of eight type II SNe and also introduce some improvements in the existing methodology. Our study explored various issues and uncertainties involved in EPM and also demonstrated its potential as a reliable redshift independent technique.


About Speaker: This is a pre-submission talk of PhD thesis work.



[112] Topic: Investigation of Star Forming Regions and Young Stellar Objects

Speaker: Archana Soam
Affiliation: ARIES
Date(yyyy-mm-dd): 2015-02-24
Time: 15:30hr
Venue: New Auditorium

Abstract: The study of magnetic fields in molecular clouds formed in various environments have enormous potential towards understanding the underlying physics behind the role played by the magnetic fields in the formation of molecular clouds and the subsequent star formation. The closer and isolated molecular clouds provide the fascinating laboratories where the importance of magnetic fields can be explored towards ongoing activities like evolution of the cloud and star formation. This needs a extensive study of magnetic fields on the large scales of these regions. Therefore, in general, the focus of this thesis is to explore the magnetic fields morphology and strength in various environments of molecular clouds to understand the open issue of the role played by magnetic fields in interstellar medium (ISM). The regions where we have mapped the magnetic fields are broadly classified into the categories viz. triggered star forming and spontaneous star forming sites. In triggered star forming regions, we have chosen the multiple bright-rimmed clouds (BRCs) and cometary globules (CGs) associated to some HII regions surrounded by a high mass star in the center. When a massive star forms, it photoionizes the surroundings, forming an HII region which display highly irregular structures such as BRCs. The radiation driven implosion process explains the photoionization induced collapse of a dense, isolated cloud that is illuminated from one side by a source of ionizing radiation. In the presence of magnetic fields, the dynamical evolution of the globule and ionized gas streaming out of the globule surface get modified significantly depending on the strength and the orientation (w.r.t the direction of incoming ionizing radiation) of the magnetic field. These HII regions are selected because of their structural simplicity and proximity to the sun. The advantage of studying multiple BRCs associated with the same HII region is that one can perform a comparative study of the magnetic field morphology at various locations of the HII region w.r.t. the direction of the ionizing radiation from the central source. Magnetic fields in a significant number of BRCs and CGs located in northern hemisphere have not been explored comprehensively. In order to examine the role played by the magnetic fields in the formation and further evolution of structures like BRCs and CGs on the periphery of HII regions, an attempt of mapping the large scale magnetic fields has been made using optical, near-IR (NIR) and submillimeter (submm) polarisation techniques. The observed polarisation is caused by the selective extinction of the light as it passes through the elongated dust grains that are aligned with their minor axis parallel to the local magnetic fields of the cloud. Moreover, our investigations reveal the effects of ionising radiation on the inherent magnetic field structures in these regions. In one part of the thesis, the plane of the sky magnetic fields morphologies in BRCs and CGs associated to HII regions Sh 2-185, Sh 131, Sh 236, Sh 126, Orion and Ophiuchus molecular clouds, are studied. Various orientations of fields lines w.r.t. the incoming high energy radiation from the nearby ionising source have been found. Based on these orientation, the evolution of BRCs and CGs are attempted to be understood by comparing the observational results with the prevailed magnetohydrodynamics (MHD) simulations. Firstly, we categorized the results of observations of the magnetic fields direction in BRCs and CGs as parallel, perpendicular and inclined w.r.t. the incoming ionising radiation. Using these observations and comparison with simulations, the radiation driven implosion (RDI) process has been attempted to be understood in this work. Along with the evolution of globules in context of the magnetic fields, we have also mapped the ionized gas using radio continuum observations towards a open cluster NGC 1893 containing a number of O type stars. The magnetic field structure have been found responsible for the morphology of these clouds. The fields lines are found to be following the ionised gas mapped using the radio observations. It has been widely accepted that the magnetic fields play an important role in the spontaneous star formation process. The influence of magnetic fields in all stages of cloud and star formation is still unclear. In a magnetic field dominated scenario for isolated low-mass star formation, the cores are envisaged to gradually condense out of a magnetically subcritical background cloud, through ambipolar diffusion. To under- stand the evolution of magnetic fields in the cores of different ages (ages determined based onto the chemical evolution), we have studied the magnetic fields in a number of prestellar cores. Magnetic fields morphology in some of the cores harboring very low luminosity objects (VeLLOs) have also been made in this thesis. These studies will help in understanding the standard models of low mass star formation and key role played by the magnetic fields in these processes. In order to understand the disk formation in the low mass stars, we have studied the magnetic field structure and following alignment/misalignment between the mean magnetic field direction and the rotation axis (the outflow axis is presumed to be the rotation axis of the core) in a core with a proto-brown dwarf candidate as a central object. Magnetic field strength have been estimated using the modified Chandrasekhar-Fermi (CF) relation. The magnetic fields direction in general is found to be parallel to the minor axes and aligned with the outflow direction from the central object. These result support the standard models of low mass star formation. This thesis also contains a small catalog containing fainter polarized standard stars available in the fields of already found brighter polarized standard stars described in the literature. These brighter standard stars, when observed with big aperture telescope, get saturated. Hence the fainter standard stars listed in this thesis will solve the issue of the saturation of the stars.


About Speaker: Archana Soam is 6th year student in ARIES, who is about to submit her thesis. Her supervisor is Dr. Maheswar Gopinathan



[113] Topic: Theoretical and Numerical Investigations of Accretion-Ejection Mechanism

Speaker: Rajiv Kumar
Affiliation: ARIES
Date(yyyy-mm-dd): 2015-02-23
Time: 15:30hr
Venue: New Auditorium

Abstract: The goal of this thesis is 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 Kumar is a sixth year student of ARIES. He is about to submit his thesis. His supervisor is Dr. Indranil Chattopadhyay



[103] Topic: Study of supernovae and massive stars and prospects with the 4m International Liquid Mirror Telescope

Speaker: Brajesh Kumar
Affiliation: ARIES, student
Date(yyyy-mm-dd): 2014-10-31
Time: 15:00hr
Venue: New Auditorium

Abstract: Massive stars are the progenitors of the most energetic explosions in the Universe such as core-collapse supernovae (CCSNe) and gamma ray bursts. During their life time they follow various evolutionary phases (e.g. supergiant, luminous blue variable and Wolf-Rayet). They strongly influence their environments through their energetic ionization radiation and powerful stellar winds. Furthermore, the formation of low- and intermediate-mass stars are also being regulated by them. The Carina nebula region, which hosts a large population of massive stars and several young star clusters, provides an ideal target for studying the feedback of massive stars. In this thesis, we investigated a wide field (32 × 31) region located in the west of the Carina nebula and centered on the massive binary WR 22. For our study, we used new optical photometry (UBVRI H_alpha), along with some low resolution spectroscopy, archival near infra-red (2MASS), and X-ray (Chandra, XMM-Newton) data. We estimated several parameters such as reddening, reddening law, etc. and also identified young stellar objects located in the region under study. Among the various types of CCSNe, Type IIb are recognized with their typical observational properties. Some of them show clear indication of double peaks in their light curves. The spectral features of these SNe show a transition between Type II and Type Ib/c events at early and later epochs, respectively. It has been noticed that the occurrence of these events is not common in volume limited surveys. In this thesis we have studied the properties of the light curve and spectral evolution of the Type IIb supernova 2011fu. The observational properties of this object show resemblance to those of SN 1993J with a possible signature of the adiabatic cooling phase. When light passes through the expanding ejecta of the SNe, it retains information about the orientation of the ejected layers. In general, CCSNe exhibit a significant level of polarization during various phases of their evolution at different wavelengths. We have investigated the broad band polarimetric properties of a Type II plateau SN 2012aw and compared it with other well-studied CCSNe of similar kinds. In the framework of the present thesis, we have also contributed to the development of the 4m International Liquid Mirror Telescope (ILMT) project which is a joint collaborative effort among different universities and research institutes in Belgium, India, Canada and Poland. We performed various experiments including the spin casting of the primary mirror, optical quality tests of the mercury surface, mylar film experiments, etc. The possible scientific capabilities and future contributions of this telescope are also discussed. We propose our plans to identify the transients (specially supernovae) with the ILMT and their further follow-up scheme. The installation of the ILMT will start very soon at the Devasthal observatory, ARIES Nainital, India.


About Speaker: Mr. Brajesh Kumar has completed his full tenure of seven years as ARIES PhD student. This talk is being organized as his thesis pre-submission talk.



[91] Topic: MULTI-WAVELENGTH STUDIES OF STAR FORMING REGIONS

Speaker: Ramkesh Yadav
Affiliation: ARIES
Date(yyyy-mm-dd): 2014-07-30
Time: 15:00hr
Venue: New Auditorium

Abstract: Star formation in extreme environments such as HII regions is always challenging and can be significantly different from that in quiet environments. HII regions are generally associated with OB stars, which usually form in clustered mode and have profound effect on the parental molecular cloud. The observations of star forming regions can be used to address several questions regarding star formation such as; what are the observational properties of different phases of star formation? How star formation proceeds within a molecular cloud? Whether the star formation is a coeval process? If not then which star forms first? Whether with the formation of massive star(s) in the region, star formation ceases or alternatively trigger(s) new generation of stars through various processes. Therefore, HII regions containing massive fragments or protostars are ideal targets to study different phases of star formation. Which mechanism (spontaneous or triggered) is dominant in a region, is necessary and vital to understand the star formation process within a complex. In this thesis we have tried to answer a few of the such interesting questions. With the advent of new data from deep optical, near-infrared, mid-infrared and X-ray surveys, a considerable interest has been evolved to study low mass young stellar objects (YSOs) as well as to study the evolution of circumstellar disks around the YSOs associated with young star clusters. Several X-ray studies of low-mass PMS stars have been carried out which revealed very strong X-ray activity. The influence of a circumstellar disk, and particularly the influence of accretion on X-ray activity has been of special interest. X-ray studies of PMS stars in star-forming regions have yielded contradictory results. Hence we have re-analyze the X-ray properties of Class II and Class III sources and the relation between rotation and X-ray activity in TTSs using the sample of the YSOs identified by Pandey et al. (2013) and the rotation period of the YSOs determined by Lata et al. (2012), Lata et al. (2014) for the YSOs in the field of young open cluster NGC 1893.


About Speaker: Ramkesh Yadav is seventh year student in ARIES, completing his PhD under the guidance of Dr. A. K. Pandey.



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

Speaker: Devesh Path Saria
Affiliation: ARIES
Date(yyyy-mm-dd): 2014-07-21
Time: 15:00hr
Venue: New Auditorium

Abstract: Astrometry of stars in star clusters was not much 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 the present study is 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 26 × 22 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 probability 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 reddening, distance, 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. The search prospered with the detection of 40 known and 9 new probable variable stars for which we present phased light curves and periods. To conclude, astrometry has entered an all new era which is going to see a rather fast boost with the GAIA data coming up in the coming years.


About Speaker: Sixth year PhD student, under the guidance of Dr. Ramakant Singh. This is his thesis pre-submission talk in ARIES.



[86] Topic: Probing Central Engine and Environments of Active Galactic Nuclei

Speaker: Ravi Joshi
Affiliation: ARIES
Date(yyyy-mm-dd): 2014-07-04
Time: 15:30hr
Venue: New Auditorium

Abstract: Owing to the high luminosity, quasars can be seen up to the very large distances, as a result their continuum and emission lines studies provides a unique tool to understand the driving parameters of central engine and the protogalaxy environment; and the absorption lines seen in their spectra give an important clue about the AGN feedback processes and the evolution of intergalactic medium, both of these features has been explored here in this thesis. The thesis probe the nature of microvariability properties of broad absorption line quasars (BALQSOs), using both radio-loud and radio-quiet subtypes. It first aim to answer the observed high fraction of variability duty cycle (similar to the blazars) for BAL quasars subclass, which are primarily believed to be radio-quiet in nature. Enlarging the sample of radio-quiet BALQSO by a factor of three, we have shown, for the first time, that only ∼16 per cent of BALQSOs show continuum variability. In a similar study, the extremely radio-loud BALQSOs have shown a similar duty cycle to that of their radio-quiet counterparts, resulting in supporting the models where the outflows, causing the broad absorption lines, may arise from the large variety of viewing angles from the jet axis or perhaps being closer to the disc plane. In a search for an elusive radio-quite counterparts of blazars, the newly discovered AGN class of weak-emission line quasars is found to be the potential candidate. Furthermore, we explore the hypothesis that, whether a weak jet component in radio-quiet AGNs is responsible for the origin of rapid small-scale optical variations or not? Using a sample of 83 radio-quiet quasars whose members has been studied for continuum variability, we have ruled out the weak jet component model in radio-quiet quasars. To probe the quasar environments, the thesis uses both the associated and intervening low ionization MgII absorption lines seen in AGN spectra. In the context the recent evidence of excess (factor ~2) number density, dN/dz, of MgII absorption systems towards blazars over the value known for normal quasars, which has questioned the canonical view of intervening and associated absorption systems, we explore towards large sample of core-dominated and lobe-dominated quasars. One of our main result was that the associated absorbers can be seen even up to mildly relativistic speeds, i.e., several times more than the canonical limit of 5000 km/s adopted in the literature for associated absorbers. The dependence of magnetic filed on the presence and/or absence of the intervening absorbers at cosmic distances along quasar sightlines having polarized light has also been explored. This study has revealed a large contribution of the intervening absorber to the enhancement of residual rotation measure at around 21cm wavelength. Finally, to understand the key question of BALQSOs being overall X-ray weak (i.e., either intrinsic or absorbed), we have explored the CIV absorption line variability to probe the physical conditions near the central engine of a very rare class of X-ray-bright BALQSOs. We found a kinematic shift and strength variability of the CIV BAL trough resulted in a largest kinematic shifts, exceeding by factor of about six as compared to the highest deceleration known till date.


About Speaker: Ravi Joshi is sixth year student of ARIES, working under the guidance of Dr. Hum Chand. This is his thesis pre-submission talk in ARIES.



[82] Topic: Study of Transients and Waves in the Solar Atmosphere

Speaker: Pradeep Kayshap
Affiliation: ARIES, 4th year student
Date(yyyy-mm-dd): 2014-06-19
Time: 15:30hr
Venue: New Auditorium

Abstract: Transients and magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere, which play a crucial role in the energy and mass transport. Therefore, understanding of the drivers and physical properties of these phenomena is at the forefront of solar physics research. Under the framework of the topic of my Ph.D. thesis, some transients at diverse spatio-temporal scales, as well as the role of MHD waves and pulses in these transients have been investigated. In the first chapter, I present an updated overview, reviewing comprehensively the physics and recent developments in various transients and MHD waves, and finally outline the plan of my various thesis chapters. In the second chapter, I report the estimated plasma properties of an active region surge using SDO/AIA, HMI observations, and conclude by our model that thermal pulse in the lower solar atmosphere can trigger the observed surge. The third chapter describes that the internal reconnection in the kinked small-scale magnetic fluxtube evolving at the polar cap of the Sun, triggers a macrospicule and associated coronal jet. The stringent 2-D MHD model depicts that the small-scale reconnection originates a velocity pulse, which steepens in the polar corona and generates the observed macrospicule and jet like plasma perturbations. Another case study of Alfven wave driven polar coronal jet, using Hinode/EIS spectral observations, is also presented in the same chapter. It is found that the reconnection in the 2-D vertical current sheet in polar corona triggers Alfven waves and related vertical plasma flows, which constitute the observed jet-like motion. In the fourth chapter, I investigate the source regions of the plasma flows and signature of the Alfvén waves in the quiet-Sun (QS) and coronal holes (CH) using the spectroscopic observations of Hinode/EIS, which have significant physical implications on the localized coronal heating and mass transport to the nascent fast solar wind. I have finally reported the first observational evidence of sausage-pinch magnetohydrodynamic (MHD) instability in a large-scale eruptive prominence tube in the fifth chapter, and discuss its physical significance in the solar coronal eruptions and magnetized plasma. In conclusion, the original research works as described in various chapters of my thesis, shed new light to the physical properties and drivers (MHD waves, pulses, instabilities) of the solar transients at diverse spatio-temporal scales.


About Speaker: Pradeep is fourth year student of ARIES, who did his PhD research under the guidance of Dr. A. K. Srivastava who was a faculty of ARIES till December 2013.







[23] Topic: Study of Ozone and other Trace Gases Distribution in the Lower Atmosphere

Speaker: Narendra Ojha
Affiliation: ARIES, 6th year student
Date(yyyy-mm-dd): 2013-05-16
Time: 15:30hr
Venue: ARIES New Lecture room

Abstract: Tropospheric ozone plays a key role in the air quality, atmospheric chemistry and climate change; however, its budget and its role in these processes are not well understood mainly due to lack of sufficient measurements. Satellite and model studies revealed elevated levels of ozone and other pollutants over the Indo-Gangetic Plain (IGP) in the Northern India; however, in lack of in situ measurements, the understanding of underlying physical, chemical and dynamical processes is very limited. Moreover, since the climatic impacts of tropospheric ozone are dependent upon its vertical distribution, the systematic and long-term measurements of ozone distribution are needed. In view of this, weekly balloon flights have been conducted to measure vertical distribution of ozone (EN-SCI 2ZV7 ECC Ozonesonde) and meteorological parameters (iMet-1-RSB 403 MHz GPS Radiosonde) from a high altitude site Nainital (79.5oE, 29.4oN, 1958 m amsl) in the central Himalayas since January 2011. Additionally, surface ozone measurements have been made at two sites, Pantnagar (79.5oE, 29.0oN, 231 m amsl) and Dehradun (78.1oE, 30.3oN, 640 m amsl), in the IGP region since 2009. Weekly air samples are also collected at Nainital for analysis of CO and greenhouse gases CO2 and CH4 in collaboration with NIES, Japan. Chemical box model (NCAR Master Mechanism), a regional chemistry transport model (WRF-Chem) and data from global models (MATCH-MPIC and MOZART) are used to understand the observed variabilities. Surface ozone at Pantnagar site in the IGP shows daytime build-up with levels sometimes as high as 100 ppbv. Ozone seasonal variations exhibit highest levels during spring (39.3±18.9 ppbv in May) and lower levels in summer-monsoon (16.8±8.9 ppbv in August) and winter (10.8±12.1 ppbv in January). This ozone seasonality is in agreement with the meteorological parameters and satellite observations of tropospheric NO2 and CO (681 hPa). A global model (MATCH-MPIC) captures the seasonality but overestimates the ozone levels. Model simulated daytime H2O2/HNO3 values are higher indicating NOx-limited chemistry over this region. Box model simulations are used to corroborate this and to estimate integrated net ozone production in a day (72.9 ppbv). Strong positive correlation (r2 = 0.96 in May) between the daytime ozone at IGP and nearby Himalayan site suggests transport of pollution from IGP to the cleaner Himalayas via boundary layer evolution. Estimated 3-monthly AOT40 index, using the observed ozone data, indicates threat for vegetations in the IGP region. Balloon-borne observations revealed large variability in the vertical distribution of ozone and meteorological parameters. Tropopause pressure from radiosonde observations agrees with the satellite (AIRS and TES) and model results, but shows dramatic variability (150-250 hPa) during winter and early spring. Lower tropospheric (2-6 km amsl) ozone shows a prominent seasonality with spring maxima (~70-110 ppbv in May) and summer-monsoon minima (~20-50 ppbv), which is consistent with the surface observations. Springtime ozone profiles are classified using MODIS fire counts, and ozone levels during high fire activity periods are observed to be higher by 19.9±4.6 ppbv in 2-4 km altitude range, as compared with low fire activity period. Signature of ozone downward transport, noticed during winter, is corroborated with observed reduction in relative humidity (radiosonde and AIRS satellite) and enhancement in potential vorticity (WRF). However, model simulated ozone profiles discern enhancements at lower altitudes than observations. A comparison of ozonesonde observations with collocated satellite (TES) retrievals shows reasonable agreement. Tropospheric column ozone (TCO) from the ozonesonde observations show a typical seasonality comprising of spring maxima (47.2±9.8 DU) and winter minima (30.4±10.1 DU). The long-term data of CO2, CH4 and CO during September 2006-December 2011, obtained from the sample analysis, has been analyzed for the seasonal variations and long-term trends. CO2 shows a prominent seasonality over Nainital with the spring maximum (395.9±5.9 ppmv in May) and post-monsoon/autumn minimum (374.4±5.8 ppmv in October). CO2 seasonal cycle at Nainital is similar to that at Mauna Loa, however, the seasonal amplitude in CO2 is much larger at Nainital (~21.5 ppmv) as compared with the Mauna Loa (~6.5 ppmv). Long-term trends in CO2, CH4 and CO have been investigated by deseasonalizing the time series and a linear regression fit. The estimated trend in CO2 over Nainital (1.88 ppmv per year) is consistent with the trends over Mauna Loa (1.60 to 2.43 ppmv per year) and global marine observations (1.64 to 2.40 ppmv per year). CH4 levels discern a small positive trend of 4 ppbv per year, while, CO levels show a negative trend of 7.3 ppbv per year.


About Speaker: Narendra is the 6th year student in ARIES working under Dr. Manish Naja.