Biweekly+Astrophysics+Seminar

IISc Astrophysics Seminars are normally held on Tuesdays at 4 pm in Lecture Hall II, the Physical Sciences building.


 * **Date/Time** || **Title** || **Venue** || **Presenter** ||
 * 04/01/2018 || **Explaining GRB prompt emission spectrum with photospheric emission model**

Although the observed spectra for the GRB prompt emission is well constrained, the underlying radiation mechanism is not very well understood. We explore the photospheric emission model by studying the Comptonization of fast cooled synchrotron photons below the photosphere when the electrons and protons are accelerated to relativistic energies by repeated dissipative events. Unlike previous simulations, we implement realistic photon to electron number ratio ~1e5 that is consistent with the observed radiative efficiency in addition to incorporating continuous energy transfer to electrons through Coulomb collisions. Using our Monte-Carlo code, we have successfully generated the observed GRB emission spectrum for electrons accelerated to highly relativistic energies with Lorentz factor ~100 by dissipative events ~40 in number, starting from moderate values of optical depth ~20. We find that the shape of the photon spectrum is independent of the initial photon energy distribution and baryonic energy content of the jet and hence independent of the emission mechanism. || Physics LH-II || Mukul Bhattacharya U. Texas, Austin ||
 * 16/01/2018 || **Pictures of dark matter using gravitational lenses**

Galaxies generically consist of an inner luminous part that is mainly baryonic matter in stars, and an outer "halo" that is mainly dark matter. Why this happens is not well understood. To improve the situation, one would like to have maps of baryonic and dark matter in many galaxies. Gravitational lensing makes this possible. So far, only a few systems are known where such mapping is feasible - but over the next few years, that situation will totally change: there will be an abundance of data, requiring a large community effort to analyse it. This talk will describe a "citizen-science" project to make pictures of dark matter with gravitational lenses, in which everyone interested - not only specialists - will be able to join the fun. || Physics LH-II || Prasenjit Saha, Univ. of Zurich ||
 * 24/01/2018 || **Quasi-periodic oscillations from post-shock accretion column of polars**

A set of strongly magnetized accreting white dwarfs (polars) shows quasi-periodic oscillations (QPOs) with frequency about a Hz in their optical luminosity. These Hz-frequency QPOs are thought to be generated by intensity variations of the emitted radiation originating at the post-shock accretion column. Thermal instability in the post-shock region, triggered by efficient cooling process at the base, is believed to be the primary reason behind the temporal variability. Here we study the structure and the dynamical properties of the post-shock accretion column including the effects of bremsstrahlung and cyclotron radiation. We find that the presence of significant cyclotron emission in optical band reduces the overall variability of the post-shock region. In the case of a larger post-shock region above the stellar surface, the effects of stratification due to stellar gravity become important. An accretion column, influenced by the strong gravity, has a smaller variability as the strength of the thermal instability at the base of the column is reduced. On the other hand, the cool, dense plasma, accumulated just above the stellar surface, may enhance the post-shock variability due to the propagation of magnetic perturbations. These characteristics of the post-shock region are consistent with the observed properties of V834 Cen and in general with Cataclysmic Variable sources that exhibit QPO frequency of about a Hz. || Physics LH-II || Prasanta Bera, IUCAA, Pune ||
 * 23/02/2018


 * Physics**
 * Colloquium** || **Vortices and the droplet growth bottleneck**

Raindrops in clouds form in about ten minutes, and this is too fast to be explained by diffusion or gravity. Remembering that clouds are turbulent, in this talk I will ask how a vortex can speed up the process of droplet growth. We show that there are two regions in this flow: close to and far away form the vortex, and the behaviour is different in each. This changes the answer. || Physics Auditorium || Rama Govindarajan, ICTS ||
 * 07/03/2018 || **Dynamics of dust clouds suspended in plasmas: a paradigm for complex multiple scale flows**

Phenomena in the dust clouds electrostatically suspended in plasmas (the fourth state of matter) replicate certain features of microscopic to astronomically large scale processes, well inside a table top plasma physics experiment. Some of the dynamical features of dusty plasma vortices are remotely shared, for example, by the galactic accretion/excretion discs and highly stable vortex flows on Jovian planets. The complex dust dynamics also shows behavioral isomorphism to many living and non-living systems operating away from their thermodynamic equilibrium. The 2D hydrodynamic formulation is recently employed to analyze the spectacular vortex flow dynamics of laboratory dusty plasmas, allowing to access both its linear and nonlinear regimes recovered in the laboratory. The characteristics of vortex and boundary flows in these highly charged dust clouds are investigated for multiple parameters, namely, the kinematic viscosity, ion drag co-efficient, neutral friction, boundary conditions and the driving field. In the low Reynolds number liner regime, the problem is also treatable as a 2D toroidal eigen value problem applicable to experimental setup, explaining vortices with induced multiplicity and spectral features introduced by boundaries. The nonlinear regime shows interscale coupling between vortices and a structural bifurcation ensuring their continued stability by means of vortex replication, isomorphic to behavior of certain biological systems and explaining such transition recovered in a more recent dusty plasma experiment. || Physics LH-II || Devendra Sharma, IPR, Gandhinagar ||
 * 09/03/2018


 * Physics**
 * Colloquium** || **Astrochemistry: Microwave Spectroscopic, Shock Wave Processing and Computational Studies**

Over the last two decades at IISc, we have established two experimental facilities that have potential use in astrochemistry, though our objective in establishing these facilities were different. We built a pulsed nozzle Fourier transform microwave spectrometer to investigate weakly bound complexes formed in a molecular beam at 2-3 K. These were usually characterized as hydrogen bonded or van der Waals complexes, though there was no consensus on what these two terms meant. Our initial experimental results helped us resolve this issue and lead a task group formed by IUPAC to redefine hydrogen bonding. Laboratory microwave spectroscopy and radio-astronomy have grown hand-in-hand and our laboratory started investigating molecular complexes that could be found in interstellar space. In parallel, we built a single pulse shock tube in collaboration with the Laboratory for Hypersonic and Shock Wave Research. This was established to carry out high temperature chemical kinetics at 1000 – 2000 K. The shock tube could also be used to investigate shock wave processing of materials in conditions similar to interstellar space. In collaboration with the University of Rennes, France, shock wave processing of various types of carbon, including fullerene were carried out. Computational chemistry has guided us in both these projects and naturally, our group started working on computational astrochemistry. We proposed an Energy, Stability and Abundance (ESA) principle recently which has helped us in predicting molecules that are likely to be observed in interstellar space. More recently, we have shown that interstellar hydrogen bonding could explain some exception to the ESA principle. This talk will summarize results from both microwave and shock wave experiments as well as computational chemistry. || Physics Auditorium || Arunan Elangannan, IPC-IISc ||
 * 13/03/2018 || **Dark matter using gravitational lenses: a citizen science project**

The universe is made of 25% Dark Matter. We have no idea what it is, but we can observe its effect. It bends space-time: big clumps of masses like galaxies act similar to a optical lens on light sources behind them. Finding and modeling those lensing situations let us determine the Dark Matter distribution of the lens, data that possibly helps answering many open questions -- but to do so, we need help from volunteers. The first part of this talk introduces the concepts of citizen science applied to strong gravitational lensing, but it's main part is a hands on demonstration of the system -- **please bring your laptop**! || Physics LH-II || Rafael Küng, Univ. of Zurich ||
 * 14/03/2018 || **Multi-observable transient astrophysics **

The most explosive and transient phenomena in the universe harbour the most powerful, natural particle accelerators like active galactic nuclei (AGNs), gamma-ray bursts (GRBs), X-ray binaries (XRBs) etc. These phenomena serve as laboratories for studying particles accelerated well beyond the TeV energies at the LHC and possibly sources of ultra high energy cosmic rays, neutrinos and gravitational waves. Despite intensive research, fundamental properties of these transients are unknown. The location and mechanisms of particle acceleration, flaring patterns and connection to these mechanisms, etc are open questions. Complexity of environments and processes often make it hard to disentangle different effects. This suggests complementing conventional observables like the broadband SED with temporal statistical observables extracted from lightcurves (power spectrum and flux distribution), polarization etc. As a population too, characteristic patterns such as origin and types of variability of these sources, contribution to cosmological backgrounds, etc., is a subject of ongoing research. In fact, study of such observables are complementary and potentially crucial cross checks to neutrino and gravitational wave observations in the multi-messenger era. In this presentation, I demonstrate the potential of using multiple observables such as temporal and polarimetric ones to understand the microphysics of extreme environments in individual transients as well as their role as a population. || Physics LH-II || Nachiketa Ckakraborty, Max-Planck-Institute fuer Kernphysik, Heidelberg ||
 * 13/04/2018


 * Physics**
 * Colloquium** || **Large Scale Anisotropy in the Universe**

The cosmological principle states that the Universe is homogeneous and isotropic on large distance scales. I will discuss the origin of this principle and its relationship with fundamental Physics. There currently exist many observations which indicate a potential violation of this principle. These include anisotropy in radio polarization, radio flux, optical polarizations, CMBR large scale anisotropies as well as the hemispherical anisotropy in CMBR. I will describe these observations and their theoretical implications. || Physics Auditorium || Pankaj Jain, IIT-Kanpur ||
 * 18/04/2018 || **Magnetohydrodynamic simulation of magnetic null-point reconnections in NOAA AR12192 initiated with an extrapolated non-force-free-field**

Magnetohydrodynamics of the solar corona is simulated numerically. The simulation is initialized with an extrapolated non-force-free magnetic field using the vector magnetogram of the active region (AR) NOAA 12192 obtained on the solar photosphere. Particularly, we focus on the magnetic reconnections occurring close to a magnetic null-point that resulted in appearance of circular chromospheric flare ribbons on October 24, 2014 around 21:21 UT, after peak of an X3.1 flare. The extrapolated field lines show the presence of the three-dimensional (3D) null near one of the polarity inversion lines, where the flare was observed. In the subsequent numerical simulation, we find magnetic reconnections occurring near the null point, where the magnetic field lines from the fan-plane of the 3D null form a X-type configuration with underlying arcade field lines. The footpoints of the dome-shaped field lines, inherent to the 3D null, show high gradients of the squashing factor. We find slipping reconnections at these quasi-separatrix layers, which are co-located with the post-flare circular brightening observed at the chromospheric heights. This demonstrates the viability of the initial non-force-free field along with the dynamics it initiates. Moreover, the initial field and its simulated evolution is found to be devoid of any flux rope, which is in congruence with the confined nature of the flare. || Physics LH-II || Avijeet Prasad, PRL ||
 * 01/08/2017 || **Probing cosmology with galaxy clustering**
 * 01/08/2017 || **Probing cosmology with galaxy clustering**
 * 01/08/2017 || **Probing cosmology with galaxy clustering**

The principal difficulty in inferring cosmological information from observations of galaxy clustering is galaxy bias, the difference between the distribution of galaxies and the distribution of the underlying dark matter. While the distribution of the gravitationally dominant dark matter can be reliably computed from first principles using cosmological N-body simulations, the distribution of galaxies cannot be robustly predicted from first principles because of uncertainties in the detailed physics of galaxy formation - gas cooling, star formation, feedback etc. To bridge the gap between N-body simulations and observed galaxies, we employ a novel technique, Subhalo Abundance Matching (SHAM) which is based on assuming a strictly monotonic relationship between galaxy luminosity and halo mass at the epoch of accretion. This implicit model for bias allows us to predict the clustering of galaxies as a function of cosmology, and thereby use the observed clustering of galaxies to place constraints on the cosmology. We carry out tests of the SHAM technique against hydrodynamic cosmological simulations, finding that SHAM successfully matches the stellar masses and luminosities of galaxies at a wide range of epochs, albeit with small amounts of scatter. I will then go on to discuss the cosmological constraints obtained from this novel technique, demonstrating that this powerful technique can provide strong cosmological constraints using only low redshift data from the nearby Universe. || Physics LH-II || Vimal Simha, University of Western Cape ||
 * 19/09/2017 || **Large deviation theory applied to turbulence dynamics: the example of rare transitions for atmosphere jets**

I will review some of the recent developments in the theoretical and mathematical aspects of the non-equilibrium statistical mechanics of turbulent flows. At the intersection between statistical mechanics, turbulence, and geophysical fluid dynamics, this field is a wonderful new playground for applied mathematics. It involves large deviation theory, stochastic partial differential equations, homogenization, and diffusion Monte-Carlo algorithms. As a paradigmatic example, we will discuss trajectories that suddenly drive turbulent flows from one attractor to a completely different one, in the stochastic barotropic quasigeostrophic equation. This equation is a generalization of the stochastic two dimensional Navier—Stokes equations that models Jupiter's atmosphere jets. We use a rare event algorithm, based on statistical mechanics, that allows to sample extremely rare trajectories. This allows us to compute transitions between attractors, with different number of jets, that could be studied using direct numerical simulations. Using this tool, we compute transition rates and instantons (most probable transition paths) and discuss there interpretation through Freidlin–Wentzell theory. || Physics Multimedia Room || Freddy Bouchet, ENS de Lyon et CNRS ||
 * 26/09/2017


 * Physics Colloquium** || **Cold gas in hot halos**

I discuss the origin and evolution of cold gas in the circumgalactic medium (CGM). Whereas hot gas is generally to faint to be seen, the cold gas can be seen both in quasar line spectroscopy and Ly-alpha emission, and is an important tracer both of galactic winds and infalling fuel for star formation. I discuss a number of interesting physical processes such as cooling induced fragmentation, the impact on small scale structure on Ly-alpha radiative transfer, and the impact of B-fields on local thermal instability. || Physics Auditorium || Siang Peng Oh, UCSB ||
 * 03/10/2017 || **Bulges in disc galaxies more compact and brighter than ellipticals at intermediate redshifts**

Examining bright disc galaxies at intermediate redshifts (0.4-1.0), in both optical and infrared using images from HST-ACS and WFC3, we have discovered a class of bulges (12%, 43 out of 358) which are more compact and brighter than elliptical galaxies. These bulges can not be classified as pseudo (which are dimmer and elongated) or classical (which are as bright and compact as ellipticals). Such bulges have not been reported in literature, even for local redshifts where there have been dense galaxy decomposition studies covering large samples. We denote them as "strange" bulges. Disc galaxies with strange bulges are intensely compact considering that they are about 1 kpc shorter in half light radius and disc scale length and about twice as massive as discs with pseudo bulges and 1.5 times more massive than those with classical bulges. These bulges are an anomaly is also reflected in the fact that the bulge accounts for more than 40% of total optical galaxy light which is a rarity at such high redshifts. Another interesting feature is that these galaxies have double the star formation rates and UV-luminosities than disc galaxies with pseudo and classical bulges which have comparable values of these two parameters. Analysing their evolution with the reference frame of 6413 bright local discs and elliptical galaxies, we examine if they are descendants of red nuggets and have recently acquired the disc through accretion. || Physics LH-II || Sonali Sachdeva, IUCAA ||
 * 17/10/2017 || **Large scale anisotropy tests with radio galaxies**

The observable Universe is simply huge! ∼ 10^26 meters in every direction, ∼ 14 billion years old and contains ∼ 10^80 hydrogen atoms. The modern cosmology is the science of the entire Universe. We, here on a small planet, can only assume that the Universe is knowable and physics is followed everywhere in the same manner. Furthermore it is reasonable to assume that the observable Universe is statistically same for all observers, located anywhere in the Universe. Today, we demand this uniformity as “Cosmological Principle” which assumes homogeneity and isotropy at large distance scales. There have been many observational tests for isotropy. The Cosmic Microwave Background Radiation (CMBR) temperature distribution is isotropic to one part in 10^5, this strongly supports the isotropy assumption. Further there are other observations supporting isotropy e.g. Ultra-High Energy Cosmic Ray (UHECR), Gamma-ray bursts (GRBs). However, there are also several observations indicating anisotropy over a very large scale (a few Gpc scale) e.g. optical polarization from quasars; radio polarization from galaxies; CMBR quadrupole, octopole and dipole alignment; number count and intensity dipole in radio galaxies etc. If these anisotropies are real and not some instrumental or observational artifacts then this potentially opens many theoretical possibilities to explore. In this talk, I will review these observations of large scale isotropy/anisotropy and discuss some existing proposals to explain observed anisotropies. || Physics LH-II || Prabhakar Tiwari, Technion, Israel ||
 * 02/11/2017 || **Efficient hydrodynamical simulation of IGM and its application**

The physical conditions prevailing in the intergalactic medium (IGM) provide important clues on how the cosmological large scale structure formation proceeded with time. High resolution Ly-α forest seen in the spectra of QSOs together with the cosmological high resolution hydrodynamical simulations allows one to constrain cosmological and astrophysical parameters related to the IGM physics. Simulations of high-z (z > 2) Ly-α forest show a tight correlation between temperature and density (the effective equation of state). On the other hand at low-z (z < 0.5) it is shown that due to different physical processes such as shock heating, various feedback processes, turbulence and radiative cooling the effective equation of state can get modified appreciably. We present a new semi-numerical method (using Gadget-2) for evolution of IGM temperature from high-z to low-z. The resultant thermal history is consistent with other low-z simulations in the past. Our method is computationally less expensive and it allows us to explore a large parameter space. The Ly-α forest spectra generated from this simulation are remarkably similar to the observed spectra. We compared these simulated spectra with unprecedented quality HST-COS Ly-α forest spectra towards 82 QSOs to constrain HI photoionization rate (Γ_HI ) with appropriate errorbars in 4 redshift bins at z < 0.5. We also compute systematic uncertainties arising from possible degenerate thermal histories of the universe. Using the cosmological radiative transfer code we find that our new constraints on Γ HI can be easily achieved without any contribution to the UV background from galaxies. Our study confirms that there is no crises at low redshift in accounting for the observed Lyman continuum photons using standard known luminous astronomical sources. || Physics LH-II || Prakash Gaikwad, IUCAA, Pune ||
 * 05/12/2017 || **Letting the data speak for themselves: what observations tell us about galaxy formation**

We infer the star formation rates in dark matter halos at different redshifts from halo merger histories expected in a Lambda CDM cosmology using Bayesian inference and Bayes ratios to restrict the model complexity, constrained to match the observed stellar mass/luminosity functions of galaxies at different redshifts and the local cluster galaxy luminosity function, which has a steeper faint end than that of field galaxies. The only other assumptions that we make are that the star formation rate of central galaxies depends on the halo mass and redshift and that when a galaxy becomes a satellite its star formation rate is quenched exponentially and it can eventually merge with the central galaxy on a dynamical friction timescale. We find that 1) the star formation in the central galaxies of high mass halos (>10e12) has to be boosted at high redshift beyond what is expected from a simple scaling of the dynamical time; 2) below z=2 the star formation in halos below 1e11 must be quenched, which is not directly expected in standard stellar feedback models and is most easily explained by some form of preheating, and implies that there is a significant old stellar population in present-day dwarf galaxies with M_star < 10e8 and steep slopes for the high redshift stellar mass and star formation rate functions 3) the stellar mass of galaxies assembles in one of three ways depending on halo mass: > 1e12 the galaxies assemble through mergers and should hence have a spheroidal morphology and between 1e11 and 1e12 (e.g MW) it assembles slowly and at z>2 has less than 5% of its mass in place, which has extreme observational consequences. || Physics Multimedia Room || Neal Katz, UMass Amherst ||
 * 06/12/2017 || **Probing the circumgalactic medium: an absorber-centric approach**

In the modern theoretical paradigm of galaxy formation and evolution, the circumgalactic medium (CGM) has received a great deal of attention as the astronomical environment "holding the keys" to a comprehensive understanding of how galaxies acquire gas to fuel their star formation and expel it in the form of chemical and mechanical feedback. The CGM is a dynamic, complex, multiphase, extended (~few 100 kpc) gaseous region surrounding galaxies, which harbors gas and metal masses comparable to those in galaxies themselves. Nonetheless, owing to its low density, direct detection of the CGM, in emission, is beyond the reach of present day telescopes. Quasar absorption line spectroscopy is an effective alternative to probe the otherwise invisible, diffuse gas in the CGM. In the talk, I will give an overview of our recent studies, using archival HST/COS spectra, on the molecular hydrogen (H2) and weak MgII absorbers, and their connections to galaxies. The prospects of CGM studies, with the advent of upcoming next-generation large telescopes, such as TMT, will also be discussed briefly. || Physics Multimedia Room || Sowgat Muzahid, Leiden Observatory ||
 * 12/12/2017 || **Unrevealing the properties of jet physics through Blazar observations**

Blazars count among the most violent sources of high energy emission in the known universe. They are characterized by highly variable nonthermal emission across the entire electromagnetic spectrum and their spectral energy distribution (SED) features two peaks. In this talk I will be discussing about a few recently observed "unconventional" properties of these blazars such as detection of very hard spectra, rapid variability (a few minute time scales), possibility of detection of orphan flare and state change during their multiwaveband observations and their implications on present understanding about these sources. I will also present results on nearby Seyfert galaxy NGC1275 on the recent observations made by ASTROSAT, NuStar and Swift-XRT. || Physics Multimedia Room || Amit Shukla, Univ of Wurzburg ||
 * 03/01/2017 || **Quasar evolution and outflows in X-ray**
 * 03/01/2017 || **Quasar evolution and outflows in X-ray**
 * 03/01/2017 || **Quasar evolution and outflows in X-ray**
 * 03/01/2017 || **Quasar evolution and outflows in X-ray**
 * 03/01/2017 || **Quasar evolution and outflows in X-ray**

The evolution of the quasar luminosity function with redshift has been a hot topic of research since last several decades. The question stands: "why are there more luminous and more numerous quasars at high redshift (z~1-2) compared to the local universe (z~0)". Popular belief is that the quasar phase of high redshift galaxies were triggered by galaxy mergers which subsequently subsided due to the ‘feedback’ due to the Active galactic nuclei (AGN), which stops the supply of matter from being accreted to the super-massive black hole. Here we present some interesting results from our sample study of local AGN in X-rays where we investigated the effects of ionised outflows on host galaxies (WAX sample). We will also present results on two other samples of Low luminosity AGN and Quasars with molecular outflows, and try to find out how exactly the AGN and its outflows impact the host galaxy. We have used the X-ray observations from XMM-Newton, Chandra and Suzaku for our sample studies. || Physics LH-II || Sibasish Laha, Queens University Belfast, UK ||
 * 24/01/2017 || **Did a Low-Mass Supernova Trigger the Formation of the Solar System? Clues from Stable Isotopes and 10Be**

About 4.6 billion years ago, some event disturbed a cloud of gas and dust, triggering the gravitational collapse that led to the formation of the solar system. A core-collapse supernova, whose shock wave is capable of compressing such a cloud, is an obvious candidate for the initiating event. This hypothesis can be tested because supernovae also produce telltale patterns of short-lived radionuclides, which would be preserved today as isotopic anomalies. Previous studies of the forensic evidence have been inconclusive, finding a pattern of isotopes differing from that produced in conventional supernova models. Here we argue that these difficulties either do not arise or are mitigated if the initiating supernova was a special type, low in mass and explosion energy. Key to our conclusion is the demonstration that short-lived 10Be can be readily synthesized in such supernovae by neutrino interactions, while anomalies in stable isotopes are suppressed. || Physics LH-II || Projjwal Banerjee, Shanghai ||
 * 21/02/2017 || **On the coupling between lower and upper atmosphere of the Sun**

Solar atmospheric structures are magnetically coupled from the photosphere through the different layers to the corona. In the past, the different atmospheric events were treated separately, particularly for the small-scale structures/events due to the limitations of observations. But, the advent of new instruments with higher spatial, temporal and spectral resolutions are improving our understanding of the small-scale events, their dynamics and coupling through different layers. Using multi-wavelength observation from the ground and space-based facilities, we study the small-scale transients in the lower atmosphere and their role in determining the dynamics and generation of waves in the upper solar atmosphere. These kinds of multi-wavelength observations may help us understanding the energy propagation through different layers which may lead to understanding the long-standing coronal heating problem. || Physics LH-II || Tanmoy Samanta, IIA || 2:00 pm || **Revealing 13 Billion Years of Thermal Evolution of the Universe**
 * 28/02/2017

The ordinary matter content of the Universe is ten thousand times hotter today than naive expectations from the otherwise well-established Lambda-CDM cosmological model. It is thought that this is because of an epoch of reionization and reheating at around redshift z ~ 6 to 10 when the Universe was about a Gyr old. Understanding when reionization took place and what caused it is one of the most important open problems in cosmology today, and has relevance for a wider array of other problems in physics. In this talk, I will discuss attempts at revealing the complete thermal evolution of the Universe. I will begin by showing that, contrary to the classical understanding, the post-reionization Universe does hold clues about reionization: the small-scale structure of the intergalactic medium (IGM) preserves a record of the cosmological thermal history. I will show how classical descriptions of this small-scale strucuture fail at redshifts z = 2--5, and after presenting a generalised theoretical characterisation that is valid at these redshifts, I will present the first measurement of this structure at redshifts 2 < z < 3 based on an unprecedented data-set of hundreds of close quasar pair spectra. I will then introduce the technique of 21 cm cosmology, which in the upcoming decades aims to use large radio telescopes such as the India-supported SKA to provide a complete three-dimensional tomographic map of the as-yet-unexplored epoch of reionization. In this direction, I will discuss my work that has produced the highest dynamic range cosmological simulations of the 21 cm signal from reionization. Finally, I will discuss attempts at tracking down the cause of reionization by focussing on the possible role played by accreting supermassive black holes. || Physics LH-II || Girish Kulkarni, Cambridge ||
 * 07/03/2017 ||  ||   || ASI Meeting Week ||
 * 14/03/2017 || **A halo model for cosmological neutral hydrogen**

The evolution of neutral hydrogen (HI) across redshifts is a powerful probe of cosmology, large scale structure in the universe and the intergalactic medium. We build an analytical halo model to describe the distribution of HI in the post-reionization universe (z ~ 5 to 0). We obtain the best-fitting parameters from a rich sample of observational data: low redshift 21-cm emission line studies, intermediate redshift intensity mapping experiments, and higher redshift Damped Lyman Alpha (DLA) observations. Our model describes the abundance and clustering of neutral hydrogen across redshifts 0 - 5, and is a useful tool for investigating different aspects of galaxy evolution as well as in the current and future intensity mapping experiments. || Physics LH-II || Hamsa Padmanabhan, ETH Zurich ||
 * 16/03/2017 || **Quenching, blackhole feedback and anisotropic thermal conduction**

Feedback from central supermassive blackholes is often invoked to explain the low star formation rates in massive galaxies. However, the detailed physics of the coupling of the injected feedback energy with the intracluster medium is still unclear. Using high-resolution magnetohydrodynamic cosmological simulations, we investigate the role of anisotropic thermal conduction in shaping the thermodynamic structure of clusters, and, in particular, in modifying the impact of black hole feedback. Stratified anisotropically conducting plasmas are formally always unstable, and thus more prone to mixing, an expectation borne out by our results. The increased mixing efficiently isotropizes the injected feedback energy which in turn significantly improves the coupling between the feedback energy and the intracluster medium. This facilitates an earlier disruption of the cool core, reduces the star formation rate by more than an order of magnitude, and results in earlier quenching despite an overall lower amount of feedback energy injected into the cluster core. These results highlight the important role of thermal conduction in establishing and maintaining quiescence of massive galaxies. || Physics LH-I || Rahul Kannan, MIT ||
 * 21/03/2017 || **The interconnection between an accreting black hole and its environment**

In active galactic nuclei (AGN) the radiation from the accretion disk is primarily emitted in the far or extreme ultraviolet, in the energy range ~10-100 eV. This UV radiation is completely absorbed by hydrogen in our own Galaxy and hence unobservable. However, this central radiation ionizes the gas and dust present in the immediate vicinity of the black hole (0.01 – 100 parsecs). This reprocessing produces characteristic signatures in the spectra of AGN – the strong broad and narrow emission lines observed in the optical and the ultraviolet (UV), and the absorption lines common in the UV and X-rays. Understanding the reprocessing of the UV continuum can (a) give crucial insight into the intimate surroundings of the black hole, and (b) provide direct observable signatures of the accretion disk environment, from which the physics of accretion onto super massive black holes may be understood.

For smaller, stellar mass black holes in binaries (BHBs), the radiation from the accretion disk is directly observable in X-rays (~ 1 keV). As X-rays do not suffer from Galactic extinction, this gives us direct observations to connect the central radiation to the properties of the gas. In case of the BHBs, the signature of matter-light reprocessing is found as absorption lines in the X-ray spectra, at > 1 keV. Hence only with the launch of the high resolution X-ray spectrometers on XMM-Newton and Chandra, at the turn of the century, this has become an addressable topic.

To study various aspects of the interaction between the black hole and its nearby environment, I have applied various photoionization tools. In my Talk I shall present the status of our understanding of the light-gas interaction in astrophysical black holes and elaborate on how they are being studied using the absorption and emission lines. || Physics LH-II || Susmita Chakravorty, IISc ||
 * 28/03/2017 || **Long lived spiral structures in galaxies**

Spiral structure in disk galaxies is modelled with a set of collisionless N-body simulations including live disks, halos, and bulges with a range of masses. Two of these simulations make long-lasting and strong two-arm spiral wave modes that last for about 5 Gyr with constant pattern speed. These two had a light stellar disk and the largest values of the Toomre Q parameter in the inner region at the time the spirals formed, suggesting the presence of a Q-barrier to wave propagation resulting from the bulge. The relative bulge mass in these cases is about 10%. Models with weak two-arm spirals had pattern speeds that followed the radial dependence of the Inner Lindblad Resonance. In addition to these, we also report a few more cases where two-armed spirals are developed and are maintained for a several rotation time scales. || Physics LH-II || Kanak Saha, IUCAA ||
 * 31/03/2017


 * Physics Colloquium** || **Coronal Mass Ejections from the Sun: how do they affect us?**

We live in a society that is increasingly reliant on spaceborne technologies. These technologies are very vulnerable to disturbances in the near-Earth space environment. It is imperative to understand the causes and consequences of such space weather disturbances in order to come up with effective mitigation strategies. One of the prime progenitors of space weather transients are Coronal Mass Ejections (CMEs), which are blobs of coronal plasma that the Sun occasionally hurls at us. We investigate the forces governing the dynamics of these CMEs as they travel from the Sun to the Earth. Many of the physical mechanisms involving CME propagation are only beginning to be understood, and there is a wealth of detailed data that offer us opportunities to test and confirm our ideas. We will conclude with an outlook on the progress we have recently made and some key questions that remain to be addressed. || Physics Auditorium || Prasad Subramanian, IISER Pune ||
 * 04/04/2017 || **The Molecular Universe: study by means of modelling, experiment and observation**

Till date more than 200 molecules have been reported in the interstellar medium (ISM). Molecules have been seen everywhere from intergalactic space to star forming region, and their types from simple molecules to long chain carbon molecules. The ISM condition is very different than that of our Earth atmosphere. How these molecules form in the low dense and cold ISM condition is very interesting.To identify these molecules in space is also very difficult. In my talk I will try to present how we can theoretically study the evolution of chemical species in ISM conditions. Also, molecules act as good traces of physical condition of molecular cloud. I will describe some observational results which helps to know physical and chemical condition of a typical low mass protostar. || Physics LH-II || Dipen Sahu, PRL ||
 * 11/04/2017 || **Probing the dark side of the Universe with strong gravitational lensing**

Most of the matter and energy content of the Universe is thought to be in the form of dark matter and dark energy. Some of the largest international projects are driven by the need to understand properties of these dark components of the Universe. Strong gravitational lensing is a phenomenon where multiple images of a distant background galaxy can be seen due to light rays being deflected by a massive galaxy in the foreground. Gravitational lenses are rare but have a wide range of applications. These include studying the distribution of dark matter and its evolution over time in galaxies and galaxy clusters, the dark matter fraction, understanding how dark energy affects growth of structure and its evolution over time. In my talk, I will present my ongoing projects which use strong lensing to address these questions. || Physics LH-II || Anupreeta More, Kavli IPMU, Japan ||
 * 18/04/2017 || **High-energy Astrophysical Radiation, Exoplanets and Astrobiology**

Astrophysics and biology might appear to be worlds apart, but a closer examination brings to light their connection at the most fundamental level. Stellar nucleosynthesis produced elements that are spread in the interplanetary medium and ended up in planets, like the Earth. Our biosphere is primarily powered by solar photons whose energy is used to produce biologically useful chemicals by a process we all know as photosynthesis. The atmosphere acts as a buffer between the astrophysical radiation environment and conditions conducive to life on Earth. I aim to explore the interaction between the two. I will describe the interaction of high-energy astrophysical radiation with extrasolar planets, their atmospheric and biological effects, with implications in astrobiology and exoplanetary science. I will also discuss how this radiation creates conditions which can be both detrimental and favorable for life to originate and evolve in the Universe. || Physics LH-II || Dimitra Atri, Blue Marble Space Institute of Science, USA ||
 * 02/05/2017 || **Tale of X-ray eclipses**

The X-ray binaries have a neutron star or a black hole that accretes matter from a companion star and emits X-rays. The size of the X-ray binaries has a wide range, from a hundredth of a light second to several hundred light seconds and the radius of the companion star also has a wide range, from earth-radius to tens of solar radius. In many X-ray binaries, the companion star subtends a significant angle to the compact star, and as a result, a good fraction of such X-ray binaries show X-ray eclipses. I will discuss X-ray eclipse observations with many space observatories that we have used to investigate various aspects of X-ray binaries like their evolution, reprocessing of the X-rays in the surrounding medium etc. In the study of orbital evolution of the binaries we had some surprising discoveries, including orbital period glitches in an X-ray binary and a massive circum-binary planet. || Physics Multimedia Room || Biswajit Paul, RRI ||
 * 21/06/2017 || **Inertial waves in rotating turbulence and in the core of the Earth**

Rotation imparts elasticity to a system so that the Coriolis force acts as the restoring force (a consequence of angular momentum conservation in the inertial frame of reference). The resulting oscillations are called inertial waves. Columnar flow structures that resemble Taylor columns have been observed in several investigations on rotating turbulence; however their mechanism of formation remains a subject of debate. In the talk, the role of inertial waves in the formation of columnar structures (by using a rapidly rotating layer of localized turbulence and buoyancy in a periodic box) will be discussed. Using helicity as a diagnostic, we have shown that the columnar structures are actually low-frequency inertial wave-packets. In the second part of the talk, I will present recent results from a strongly-forced geodynamo simulation, where, for the first-time, we have identified internally-driven inertial waves triggered from the equatorial region. Our results suggest that these waves help maintain the coherence of the columnar flow in the core. The potential role of these waves in the dynamo generation is under investigation and will be briefly discussed. || Physics Multimedia Room || Avishek Ranjan, University of Cambridge ||
 * 27/06/2017 || **Recent Developments in Reconnection Theory: the Plasmoid Instability and Self-Generated Turbulence**

In recent years, new developments in reconnection theory have challenged classical nonlinear reconnection models. One of these developments is the so-called plasmoid instability of thin current sheets. Within the framework of the resistive MHD model, this instability alters qualitatively the predictions of the classical Sweet-Parker model, leading to a new nonlinear regime of fast reconnection in which the reconnection rate itself becomes independent of the Lundquist number. This regime has also been seen in Hall MHD as well as fully kinetic simulations. Plasmoids, which can grow by coalescence to large sizes, provide a powerful mechanism for coupling between large (global) and small (kinetic) scales as well as an efficient accelerator of particles to high energies. A new phase diagram of fast reconnection has been proposed, guiding the design of experiments. In three dimensions, the instability produces self-generated and strongly anisotropic turbulence in which the reconnection rate for the mean magnetic field remains approximately at the two-dimensional value, but the energy spectrum deviates strongly from standard MHD turbulence phenomenology. || Physics Multimedia Room || Amitava Bhattacharjee, Princeton University ||
 * 05/01/2016 ||  || Physics LH-II || Bhargav Vaidya, Torino ||
 * 19/01/2016 ||  || Physics LH-II || Sonali Sachdeva, IUCAA ||
 * 16/02/2016 ||  || Physics LH-II || Girish Kulkarni, Cambridge ||
 * 25/02/2016 ||  || Physics LH-II || Surajit Paul, Univ. of Pune ||
 * 08/03/2016 ||  || Physics LH-II || Tarun Deep Saini, IISc ||
 * 15/03/2016 ||  || Physics LH-II || Ruta Kale, NCRA ||
 * 29/03/2016 ||  || Physics LH-II || Vikram Khaire, IUCAA ||
 * 10/05/2016 || **The timing behaviour of neutron star X-ray binaries in the thermal Comptonization context**
 * 25/02/2016 ||  || Physics LH-II || Surajit Paul, Univ. of Pune ||
 * 08/03/2016 ||  || Physics LH-II || Tarun Deep Saini, IISc ||
 * 15/03/2016 ||  || Physics LH-II || Ruta Kale, NCRA ||
 * 29/03/2016 ||  || Physics LH-II || Vikram Khaire, IUCAA ||
 * 10/05/2016 || **The timing behaviour of neutron star X-ray binaries in the thermal Comptonization context**

Neutron star low-mass X-ray binaries exhibit X-ray variability in the order of milliseconds. In the frequency domain these are termed as kilohertz quasi periodic oscillations (kHz QPOs). To interpret the energy dependence of the r.m.s. and phase lag of these kHz QPO in a thermal Comptonization model framework, we solve the linearised time-dependent Kompaneets equation which describes the Comptonization process in the non-relativistic limit. We consider oscillatory perturbations in the soft photon source or in the heating rate of the plasma. The model incorporates the possibility of a fraction of the Comptonized photons η, impinging back into the soft photon source. We show that the model is capable of estimating parameters such as the size of the corona, but it is sensitive to the details of the time averaged spectral modeling. Hence we apply the model to estimate the size of the corona L as a function of lower kHz QPO frequency for two different spectral models namely the hot and cold seed models. We find that for the hot-seed spectral model the size of the corona increases with decreasing kHz QPO frequency, while there is no such trend when the spectral model is the cold-seed one. We also obtain the average ranges of L and η for both spectral models. Finally, we develop a Monte Carlo scheme for the Comptonization process and use it to estimate η for different geometries and compare the values with those required by the observations. || Physics LH-II || Nagendra Kumar, IUCAA ||
 * 21/06/2016 || **A production scenario of the galactic strangelets and an estimation of their possible flux in the solar neighborhood **

Finite lumps of strange quark matter in the form of strangelets, the theorized absolute ground state of QCD, are supposed to be more stable than the Fe56 nuclei. Recent simulation studies suggest that a major source of strangelets in the Galaxy may be the fragmentation of bulk strange matter tidally released in the merger of strange stars in compact binary stellar systems. Here, we determine a plausible baryon number (or mass) distribution of such strangelets by invoking a statistical disassembly model often used in nuclear systems. Strangelets, thus produced, are likely to be accelerated by the shock front generated in the same merger event thereby gaining a power law energy spectrum with spectral index close to -2. We estimate the fluxes of such accelerated strangelets of different masses in the neighborhood of the Sun considering diffusive propagation of strangelets in the stochastic magnetic field of the interstellar medium. The determined integral fluxes are found to be consistent with the null results of the PAMELA experiment. The reported limit of sensitivity of the AMS-02 experiment suggests that the experiment should be able to detect strangelet events, as per the prediction of the proposed model, thereby (possibly) vindicating the strange matter hypothesis. || Physics LH-II || Sayan Biswas, Bose Institute, Kolkata ||
 * 12/07/2016 || **Estimating power spectrum from interferometric data**

Second order statistical measures like structure function or power spectrum are known to be powerful tools for various astrophysical and cosmological studies. They are equally useful in quantifying the turbulent small scale structures of the diffuse interstellar medium in the local universe, or the high redshift cosmological signals like the neutral hydrogen 21 cm signal from the EoR (Epoch of Reionization) or post-EoR era. In this presentation, I will talk about efficien Large Scale Anisotropy in the Universe t estimation of power spectrum from the radio interferometric observations. I will briefly describe improved estimators developed recently to handle some of the complicated issues like large data volume, noise bias, foreground contamination etc. that are relevant for both astrophysical and cosmological studies. || Physics LH-II || Nirupam Roy, IISc ||
 * 02/08/2016 || **High Time Resolution Pulsar Studies with the GMRT**

The Giant Metrewave Radio Telescope (GMRT), owing to its high sensitivity and extensive frequency coverage at metre and centimetre wavelengths, is an attractive prospect for high time resolution studies of pulsars. Further, the recent development of a real-time coherent dedispersion pipeline for the existing back-end allows one to completely eliminate the dispersive effects of the interstellar medium. In this presentation, I will talk about our efforts towards the development of this coherent dedispersion system, and present recent science results that have been obtained using it. In particular, I will present our work on probing the polarisation and spectral properties of microstructure emission in pulsars using the GMRT. The high sensitivity of the GMRT allows us to detect microstructure emission in a number of pulsars, including ones where such emission has never been detected before. I will discuss the algorithms we have developed for automated characterisation of microstructure timescales, along with preliminary results from a statistical study of micropulses using this system. Lastly, I will highlight the potential for such studies with the upgraded GMRT, which will have bandwidths ~ 8 times larger than the current system, using a wide bandwidth coherent dedispersion system that we have commissioned very recently. || Physics LH-II || Kishalay De, IISc ||
 * 09/08/2016 || **Gravitational Lensing with SN Ia in the SNLS**

Type Ia supernovae have become an essential tool of modern observational cosmology. By studying the distance-redshift relation of a large number of supernovae, the nature of dark energy can be unveiled. Distances to Type Ia SNe are however affected by gravitational lensing which can induce systematic effects in the measurement of cosmology. The majority of the supernovae is slightly demagnified whereas a small fraction is significantly magnified due to the mass distribution along the line of sight. This causes naturally an additional dispersion in the observed magnitudes. There are two different ways to estimate the magnification of a supernova. A first method consists in comparing the supernova luminosity, which is measured to about 15% precision, to the mean SN luminosity at the same redshift. Another estimate can be obtained from predicting the magnification induced by the foreground matter density modeled from the measurements of the luminosity of the galaxies with an initial prior on the mass-luminosity relation of the galaxies. A positive correlation between these 2 estimates will signify the detection of lensing magnification. It will also make it possible to tune the initially used mass-luminosity relation resulting in an independent measurement of the dark matter clustering based on the luminosity of SNe Ia. Evidently, this measurement depends crucially on the detection of this correlation also referred to as the lensing signal. This thesis is dedicated to the measurement of the lensing signal in the SNLS 5-year sample. || Physics LH-II || Ayan Mitra, UPMC, Paris ||
 * 29/08/2016 || **Cosmological Inflation, Primordial Magnetic Fields and their non-Gaussian imprints**

I will start with a brief introduction to cosmological inflation and the observational evidence for cosmic magnetic fields. I will then outline various mechanisms for generation of primordial magnetic fields from inflation and discuss the constraints arising from the strong coupling, backreaction and the anisotropies due to the induced bispectrum of the generated magnetic fields for the simplest gauge invariant model of inflationary magnetogenesis. In the second part of my talk, I will discuss non-Gaussian imprints of cosmic magnetic fields by means of a cross-correlation between the primordial curvature perturbations and magnetic fields. Such a correlation serves as a new contribution to the non-Gaussian signatures induced by primordial magnetic fields. We obtain a simple consistency relation for this cross-correlation in the squeezed limit while the signal is maximized for the flattened configuration where the magnetic non-linear parameter becomes large. Towards the end, I will also discuss primordial magnetogenesis in a non-singular bouncing scenario wherein a scale invariant spectrum of magnetic fields can be obtained. || Physics Multimedia Room || Rajeev K Jain, Univ. Southern Denmark ||
 * 30/08/2016 || **Radio frequency heating and current drive in fusion plasmas**

It is widely recognized that the energy supply is one of the largest challenges that mankind will be facing during this century. Nuclear fusion intends to be one of these sources, its main objective being to transform the energy paradigm: from today's dependence on natural resources and environmental impact into a technology-dependent resource. This talk intends to give a picture of where fusion research stands today and the perspectives: the achievements, the difficulties, the current status of fusion experiments which will demonstrate the scientific feasibility of fusion power, and the perspectives toward the first demonstration power plant, DEMO. We have developed the numerical simulation model to understand the radio frequency waves and its implications on auxiliary heating and current drive, which is important for the steady state operation of the present and future fusion reactors. I will discuss the model with the physical processes involved and present results. || Physics Multimedia Room || Animesh Kuley, Univ. of California, Irvine ||
 * 13/09/2016 || **Back to Dark Matter Astrophysics for Dark Matter Direct Detection Searches**

Properties of dark matter (DM), determined through direct (and, also, indirect) detection experiments, depend on synergies between astrophysics and particle physics. For example, the density and velocity distribution function of the dark matter in our neighborhood is crucial in determining the collision rates in DM direct detection experiments. Unfortunately, there is a wide dispersion of observationally determined DM density (and profiles); moreover, the `standard halo model (SHO)', unfavored by observations and simulations, is predominantly used by the particle physics community. Using some of the latest compilation of observational tracers, we make the first ever observational estimate of the DM phase-space of the Milky Way halo up to 200 Kpc (i.e almost r200). Our results bring out deviations from the SHO as well as differences from numerical simulation predictions, and points to the importance of precise determination of visible matter density and the local standard of rest. Finally, we make some comments on the prospects using data from GAIA, and future missions like THEIA. || Physics LH-II || Subhabrata Majumdar, TIFR ||
 * 16/09/2016


 * Physics Colloquium** || **Lenticular Galaxies: At the Join of Hubble's Tuning Fork**

Lenticular galaxies have a bulge and disk but no spiral arms. The prominent bulge makes lenticulars similar to elliptical galaxies, while the disk makes them similar to spiral galaxies, but with no arms. The overall structure of galaxies like these, and even more complex ones, can usually be described in terms of a several parameters which act as proxies for the luminosity, size and shape of galaxy structural components. I will discuss in my talk how current observations and software allow these parameters to be determined for large samples, and how the statistical correlations between parameters can shed light on the origin and evolution of the galaxies. I will primarily focus on lenticulars. || Physics Auditorium || Ajit Kembhavi, IUCAA, Pune ||
 * 20/09/2016 || **Strong Gravity Frame-dragging Effect in the Astrophysical Context**

I will discuss on the exact frame-dragging (Lense-Thirring) frequency in the Kerr spacetime as well as inside and outside of a rotating neutron star. In case of a Kerr black hole (Kerr parameter a <= 1), the precession frequency becomes arbitrarily high very near the ergoregion but this frequency remains always finite and well-behaved in case of a naked singularity (a > 1), as it is proportional to the distance 'r' instead of the 'inverse cube law of distance' in all other known astrophysical cases. This feature can help us to distinguish between a black hole and a naked singularity, if it in fact exists. In case of frame-dragging rate along the equatorial distance of a pulsar, LT frequency decreases initially away from the centre, becomes negligibly small well before the surface of it, rises again and finally approaches to a small value at the surface. Moving from the equator to the pole, it is observed that this local maximum and minimum in the frame dragging rate along the equator disappears after crossing a critical angle. We also show that the magnetic field has a non-negligible impact on frame dragging. The maximum effect of the magnetic field appears along the polar direction, where the LT frequency decreases with increase in magnetic field, and along the equatorial direction, where its magnitude increases. For intermediate angles, the effect of the magnetic field decreases, and goes through a minimum for a particular angular value at which magnetic field has no effect on frame-dragging. Beyond that particular angle LT effect increases with increasing magnetic field. We try to identify this 'Null Region' for the case of a magnetized neutron star, both inside and outside, as a function of the magnetic field. || Physics LH-II || Chandrachur Chakraborty, TIFR ||
 * 27/09/2016 || **Closed Universe and Cosmic Microwave Background**

While recent observations indicate that the geometry of our Universe is spatially flat, the experimental error bars allow the possibility of a spatially curved geometry (a closed Universe). Most recent data is compatible with a closed Universe with a radius of at least 4.5 times that of the surface of last scattering. We study the evolution of the background geometry and gauge-invariant scalar perturbations in an inflationary closed FLRW model and calculate the primordial power spectrum. We find that the inflationary dynamics is modified due to the presence of spatial curvature, leading to corrections to the nearly scale invariant power spectrum at the end of inflation. When evolved to the surface of last scattering, the resulting temperature anisotropy spectrum shows deficit of power at low multipoles. By comparing our results with the recent Planck data, we discuss the role of spatial curvature in accounting for CMB anomalies and in the estimation of the spatial curvature. || Physics LH-II || Brajesh Gupt, Penn. State Univ. || 11:30 am || **Flux Transport Dynamo models: Understanding the solar magnetic field generation process**
 * 28/09/2016

Solar cycles are nothing but the magnetic cycle of sun and in order to understand solar cycle and its properties, we need to understand how sun is generating its own magnetic field and organizing them. Flux Transport model is the most successful model to understand the solar magnetic field generation process. But it has some inherent limitations. In most of the flux transport dynamo models, a single cell meridional circulation is used and recently there are several observational evidences that the meridional circulation of Sun may not have a single cell structure rather it might have a double cell or multi-cell structure. I shall discuss that this new observations is not imposing any serious threat and our model works perfectly fine. Many processes in this models are inherently 3D and in 2D we can model them very crudely by using some simple parametric form. So I shall explain next generation 3D Flux Transport Dynamo model which will be more realistic in model structure. Build up of Solar Polar fields using this model will also be discussed. Apart from that we have included high resolution observed non-axisymmetric convective flows from SDO Dopplergram data in our model to see its behaviour on the Babcock-Leighton process and to put a better constraints on the surface diffusivity value. || Physics LH-II || Gopal Hazra, IISc ||
 * 04/10/2016 || **Dark Energy Survey: Dark matter and Baryons**

Dark Energy Survey (DES) is one of the largest cosmological surveys currently on the sky. In the most part of my talk I will present some of the early science results from the weak lensing (WL) of DES Science Verification (SV) data. I will show the measurement and testing of shears from SV data and present the selection of the foreground galaxy sample. I will talk about the indirect detection of dark matter which will be measured using the mass map generated from the WL shear. Quantitatively, the correlation between the dark matter and the foreground galaxies and clusters matches with the semi-analytical simulations. I will show some of the initial physical parameters of the pressure profile from the cross correlation signal which use the DES WL and Planck Sunyaev--Zel'dovich maps. In the latter years of DES I expect to improve the constraints of pressure profiles from the DES groups and clusters. || Physics Multimedia Room || Vinu Vikram, Argonne Nat. Lab. ||
 * 25/10/2016 || **The cosmic web and the Spin of Galaxies**

Galaxies gain angular momentum in the linear stage of structure formation according to Tidal torque theory. This theory predicts alignments between the spin of halos and the tidal shear field. However, non-linear evolution and angular momentum acquisition may alter this prediction significantly. In this talk, I will discuss the issue of angular momentum of galaxies and its current status. Further, I will present our observational results of alignments of galaxies with large scale structure. We use a reconstruction of cosmic shear field from observed peculiar velocities combined with spin axes extracted from observed data sets to test whether or not galaxies appear aligned with principal axes of the shear field. We use 2MRS catalog for our study. We find an alignment for a subsample of galaxies in 2MRS. Specifically, the spin axis of elliptical galaxies that are used in velocity field reconstruction, show statistically significant alignment with the axis of the fastest collapse. || Physics LH-II || Isha Pahwa, IUCAA, Pune || 1:30 pm || **Star Cluster Dynamics and Merging Black Hole Binaries**
 * 03/11/2016

Detection of gravitational waves from merging black hole binaries by the advanced Laser Interferometer Gravitational-Wave Observatories (aLIGO) have reignited widespread interest in understanding the astrophysical origins of black hole binaries. Massive star clusters have been shown to be efficient factories of binary black holes that would merge in the local universe. I will talk about massive star cluster evolution with a focus on how black holes form and dynamically evolve in them. I will discuss our key results on dynamically created binary black holes and their detectable properties and put them in the context of the ground-breaking discoveries by aLIGO. || Physics Auditorium || Sourav Chatterjee, Northwestern Univ. ||
 * 09/11/2016 || **Kinetic Physics of Turbulent Collisionless Astrophysical Plasmas**

Plasmas are ubiquitous in nature. Many astrophysical plasmas (e.g. Solar wind, galactic cooling flows, some black hole accretion disks and planetary magnetospheres) are observed or believed to be almost collisionless as well as in a turbulent state. Under such conditions, conventional fluid theories of plasma turbulence and dissipation become questionable. We provide a general overview of the field and discuss some of the recent results related to dissipation in collisionless plasmas, transition of turbulence from fluid to kinetic regimes as well as some astrophysical applications. || Physics Multimedia Room || Tulasi Nandan Parashar, University of Delaware ||
 * 15/11/2016 || **The impact of star formation driven galactic winds on the circumgalactic medium**

I will present a series of idealized three-dimensional hydrodynamic simulations that we use to study the dynamics and thermal structure of the circumgalactic medium (CGM). Our simulations quantify the role of cooling, galactic winds driven by stellar feedback, and cosmological accretion of gas in setting the properties of the CGM in dark matter halos ranging from 10^11–10^12 M_sun. As in calculations without stellar feedback, we find that above a critical halo mass of 10^11.5 M_sun, halo gas is supported by thermal pressure created in the virial shock. The thermal properties of the halo gas at small radii (near any central galaxy) are regulated by feedback triggered when t_cool/ t_ff ≤ 10 in the hot halo gas. Below the critical halo mass, however, there is no thermally supported halo and self-regulation at t_cool/ t_ff~10 does not apply. Instead, the halo gas properties are determined by the interaction between the cosmological inflow of gas and the outgoing galactic winds. The halo gas is not in hydrostatic equilibrium, but is supported against gravity by bulk flows (turbulence and coherent inflow/outflow), and its phase structure depends on both the energy per unit mass and the mass-loading factor of the galaxy outflows. The properties of our idealized simulations can account for some of the properties of the multiphase halo gas inferred from HST-COS observations, including the presence of significant mass at a wide range of temperatures, and the characteristic OVI column densities and kinematics. I will also (time permitting) briefly mention a related project in which we adopt a similar idealized approach applied to the launching of galactic winds by supernovae with the goal of self-consistently determining how the wind velocity and mass-loading scale with host galaxy properties. || Physics LH-II || Drummond Fielding, U. C. Berkely, USA ||
 * 29/11/2016 || **The Complete Local-Volume Groups Sample: Radio properties and feedback implications of galaxy groups in the Local Universe**

Much of the evolution of galaxies takes place in groups where feedback has the greatest impact on galaxy formation. By using an optically selected, statistically complete sample of 53 nearby groups (CLoGS), observed at both radio (GMRT) and X-ray (Chandra and XMM-Newton) frequencies, my work aims to characterize the radio-AGN population in groups and examine their impact on the intra-group gas and member galaxies. In this regard, first results from low-frequency GMRT radio images of the nearby (<80 Mpc) central brightest group elliptical from the high richness CLoGS sub-sample are presented at 235 and 610 MHz. Using the sensitivity to older electron populations at 235 MHz and the resolution of 610 MHz as a key to identify past and current AGN activity, I will discuss the properties that central group radio sources present in our sample (radio morphology, spectral index, energetics etc), along with information on the group environment that they lie into, with combination of the radio results with findings from the X-ray observations. || Physics LH-II || Konstantinos Kolokythas, IUCAA, Pune ||
 * 05/12/2016 || **Principle of Least Action in General Relativity**

Constructing a well-posed variational principle and characterizing the appropriate degrees of freedom that need to be fixed at the boundary are non-trivial issues in general relativity. I will discuss a few toy examples in classical mechanics and field theory before going into general relativity. For spacelike and timelike boundaries I will show that the action principle for general relativity is well posed, only when a suitable counter-term [the Gibbons-Hawking-York (GHY) counter-term] is added to the action principle. Also I will show that the degrees of freedom to be fixed on the boundary are contained in the induced 3-metric. These results, however, do not directly generalize to null boundaries on which the 3-metric becomes degenerate. In this talk I will address the following questions: (i) What is the counter-term that may be added on a null boundary to make the variational principle well-posed? (ii) How do we characterize the degrees of freedom which need to be fixed at the null boundary? || Physics LH-II || Sumanta Chakraborty, IACS Kolkata ||
 * 06/12/2016 || ** On the spectral problem for the gyrokinetic-Vlasov equation. **

In this talk we present the linear theory of collisionless kinetic modes in a toroidal geometry, such as ionic instabilities, by using the exact geometric reduction of the Vlasov equation yielded by waterbag invariants, which are reminiscent of the geometric Liouville invariants. For high toroidal wavenumber, using a WKB-type analysis in a coordinate system aligned with the magnetic field lines, we demonstrate that one can construct eigenmode solutions of the two-dimensional integro-differential operator in toroidal geometry by solving a series of one-dimensional integral equations in the poloidal direction coupled to a one-dimensional Schroedinger equation in the radial direction. After showing some properties of the spectral problem, we illustrate such construction by numerical examples in the context of tokamak plasmas such as the CYCLONE benchmark. || Physics LH-II || Nicolas Besse, Observatoire de la Cote d"Azur, France ||
 * 08/12/2016


 * Physics Colloquium** || **Understanding general Relativity after 100 years: a novel perspective**

This year General Relativity is 100 years old. I would discuss the kind of insights and perspective we have evolved over the period, and what directions that point to for further probing and exploration? || Physics Multimedia Room || Naresh Dadhich, Jamia Millia Islamia, Delhi ||
 * 15/12/2016 || **Circularly Polarized Light from Magnetized Current Filaments**

We investigate the radiation spectra and degree of circular polarization emitted by plasma electrons due to their motion in the fields generated by Weibel Instability/Current Filamentation Instability (WI/CFI) in magnetized/unmagnetized interpenetrating plasma flows. The detailed kinetic processes, the radiation and its polarization signatures are modelled using a combination of particle-in-cell (PIC) simulations using OSIRIS framework and a post-processing radiation diagnostic, jRad. We explore the role of plasma composition (electron-positron vs electron-ion) and initial magnetization on the degree of circular polarization of the radiation emitted by electrons confined in the current filaments generated due to WI/CFI. It has been found that the field structures in electron-ion plasmas with high ion-electron mass ratios (mi/me>>1) evolve at the ion time scales. When the plasma is magnetized initially, an azimuthal drift in the plasma electron appears at the edge of the filament. The steady motion of the electrons within the magnetized current filaments gives rise to the emission of circularly polarized radiation. We find that the net degree of circular polarization of radiation from multiple filaments is the average of contribution from individual filaments. We also find that the degree of circular polarization increases with the magnetization, and that it saturates at ~20% for very high magnetization values. In addition, the degree of circular polarisation also increases for larger mi/me. This study is of relevance to understand the recent observation of circular polarization in Gamma Ray Burst afterglows as well as for laboratory experiments of colliding plasmas. || Physics LH-II || Ujjwal Sinha, GoLP/IPFN, Lisbon || Turbulent reacting flows are ubiquitous in engines: for e.g. in gas turbines, ramjets, scramjets, rockets and in nature: for e.g. in forest fires, the entire atmosphere or supernovae. These are extremely rich: multiscale, multi-physics phenomena, which span from the hydrodynamic scales, of the order of a meter for an engine to thousands of kilometers for a supernova down to sub-millimeter scale flame thickness (for both chemical and nuclear flames) to the angstrom level molecular scales where chemical or nuclear reactions occur. To understand the fundamentals of turbulence flame interaction, recently a Lagrangian viewpoint called Flame Particle Tracking (FPT) has been introduced [1,2]. Flame particles are surface points [3] that always remain embedded on, by comoving with a given iso-scalar surface within a flame. In this talk, using Direct Numerical Simulations of Hydrogen-Air chemical flames and FPT we would study the finite lifetime of such flame particles and the time evolution of several associated properties. This could allow us to further understand how turbulence creates and destroys flame surface, which eventually determines the statistical propagation rate i.e. turbulent flame speed or enhanced ignitability [4]. Next using a global viewpoint, aided by theory and experiments, we will look into turbulent flame speed [5-7] which determines whether a hydrocarbon flame could be stabilized in a high speed engine flow, or whether a nuclear fusion powered deflagration would transition to detonation towards a supernova Ia. Recent experiments on expanding turbulent premixed flames suggest a self-similar scaling law for turbulent flame speed which if proven to be generally valid, could offer a route for deflagration to detonation transition in cases involving extreme scale separation such as in a supernova Ia.
 * || **EARLIER TALKS** ||  ||   ||
 * 11/08/2015 || **Local and Global Viewpoints to Analyse Turbulence-Flame Interaction**
 * || **EARLIER TALKS** ||  ||   ||
 * 11/08/2015 || **Local and Global Viewpoints to Analyse Turbulence-Flame Interaction**
 * || **EARLIER TALKS** ||  ||   ||
 * 11/08/2015 || **Local and Global Viewpoints to Analyse Turbulence-Flame Interaction**
 * || **EARLIER TALKS** ||  ||   ||
 * 11/08/2015 || **Local and Global Viewpoints to Analyse Turbulence-Flame Interaction**
 * 11/08/2015 || **Local and Global Viewpoints to Analyse Turbulence-Flame Interaction**

References: [1] S. Chaudhuri, Proceedings of the Combustion Institute 35, 1305 (2015). [2] S. Chaudhuri, Physical Review E 91, 021001 (2015). [3] S. B. Pope, International Journal of Engineering Science 26, 445 (1988). [4] F. Wu, A. Saha, S. Chaudhuri, and C. K. Law, Physical Review Letters 113 (2014). [5] S. Chaudhuri, F. Wu, D. Zhu, and C. K. Law, Physical Review Letters 108 (2012). [6] S. Chaudhuri, V. y. Akkerman, and C. K. Law, Physical Review E 84, 026322 (2011). [7] S. Chaudhuri, F. Wu, and C. K. Law, Physical Review E 88, 033005 (2013). || Physics LH-II || Swetaprovo Chaudhuri, Department of Aerospace Engineering, IISc ||
 * 25/08/2015 || **Neutrino Astrophysics: What we have learned and the way forward**

Neutrinos are produced in a variety of astrophysical sources which comprise our Sun, the Earth, the Early Universe and in explosive environments such as core-collapse supernovae, gamma ray bursts. These weakly interacting particles can travel extremely large distances without changing their properties, carrying unique information about their sources. However, the neutrino fluxes of different flavors may get mixed while traversing an astrophysical environment, specially dense environments like core-collapse supernovae. Understanding of the neutrino evolution in such dense medium can resolve several unanswered questions about the stellar dynamics. On the other hand the recently discovered high energy (PeV) neutrinos in IceCube experiment have also provided the "smoking-gun" signal of hadronic nature of cosmic-ray acceleration. Although, the precise origin of these neutrinos is yet to be determined, they have successfully put strong limits on several models of ultra-high energy neutrinos. In this talk, we will briefly review the implications of neutrino flavor conversion during stellar core collapse and emphasize the progress in our understanding of high energy neutrino astrophysics in light of the spectacular IceCube neutrino observations. || Physics LH-II || Sovan Chakraborty ||
 * 10/11/2015 ||  || Physics LH-II || Joe P. Ninan, TIFR ||
 * 24/11/2015 ||  || Physics LH-II || Pratik Majumdar, SINP ||
 * 14/12/2015 ||  || Multimedia Room || Arnab Rai Choudhuri, IISc ||
 * 13/01/2015 || **Helicity and Energy Flux Transport in Emerging Solar Active Regions**
 * 13/01/2015 || **Helicity and Energy Flux Transport in Emerging Solar Active Regions**

Solar magnetic fields, together with their helicity, are created in the convection zone by various dynamo processes. These fields and helicity are transported into the corona through solar photosphere and finally released into the interplanetary space via various energetic processes. Thus accurate estimation of energy and helicity budgets in the coronal volume above active region is a vital and primary step for predicting the occurrence of an eruption. With the availability of continuous time sequence vector magnetic field measurements from recent space observatories, it has become possible to study for a physical understanding of eruptions. Therefore, in this talk, I shall discuss the details of magnetic helicity and energy in the active region magnetic structure, and their measurement procedures and few results. In addition, I will also discuss methods of coronal magnetic field reconstruction from boundary observations, as they are required for the estimation of volume integrated relative magnetic helicity of the active region. || Physics LH-II || Vemareddy Panditi, IIA ||
 * 27/01/2015 || **Turbulence in space and astrophysical plasmas - from fluid to kinetic scales **

Plasma turbulence is observed in a wide variety of space and astrophysical objects. Turbulence is driven by injecting energy at large scales through stirring or instabilities. This energy cascades forward to smaller scales by nonlinear interactions described by the framework of magnetohydrodynamics (MHD) which treats the plasma as a conducting fluid. I will briefly review the phenomenological models and observations that describe this cascade. At small scales, the fluid description of MHD breaks down and individual particle motion becomes important. This is also where kinetic damping comes into play and dissipates the turbulent energy into heat. We investigate this entire process using MHD and particle-in-cell (PIC) simulations. We find that both formulations agree nicely at large scales in their energy dynamics and energy spectra. Very thin current sheets are seen to play an important role in the energy dissipation process. PIC simulations reveal that their thickness is limited to the skin-depth, which MHD is not able to capture. This shows that kinetic physics has important implications for a variety of processes in plasma astrophysics. || Physics LH-II || Kirit Makwana, Chicago ||
 * 10/02/2015 || **Kinematics and emission from a relativistic magnetized jet **

We present general relativistic models of treating kinematics and emission of plasma flow embedded in an accretion disk-jet system in the vicinity of the SMBH. The model treats the orbital kinematics of flows which transit from the disk onto a relativistic jet shaped by a magnetic surface with foot points near the innermost stable circular orbit. The emission model includes Doppler and gravitational shifts, aberration, light bending and time delay effects on the radiatively driven plasma. Light curves are simulated for studying effects of the relativistic beaming, the QPO phenomena and aperiodic variability over timescales ranging between a few 1000 s and a few days. A power law power spectral density shape results with a typical slope of $\sim -2$. The models developed can be applied to radio, optical and X-ray emission from a wide class of compact objects including actively accreting AGN, X-ray binaries and neutron stars. || Physics LH-II || Arun Mangalam, IIA ||
 * 24/02/2015 || **The locations of gravitational collapse: analytical insights and open issues **

The study of cosmological large scale structure using large volume galaxy surveys aided by high resolution numerical simulations is now well into its "precision era". Interpreting these precise measurements requires accurate modelling of the underlying cosmology and, in particular, the interplay of gravity and stochastic initial fluctuations that leads to the formation of gravitationally bound dark matter clumps ("halos"). In this context, analytical approximations such as the excursion set approach are a very useful tool that complement numerical simulations of structure formation. I will introduce the basic ideas underlying the excursion set approach and discuss recent improvements in identifying the locations of gravitational collapse; these improvements have brought the predictions of this approach from "order of magnitude" to "ten percent" agreement with the more accurate results of numerical simulations. I will then highlight some of the open issues and problems in this approach. One of the most interesting of these is a subtle mis-estimate of the collapse time of a given high density peak, which has dramatic consequences for structure formation in the presence of a truncated spectrum of initial fluctuations ("warm dark matter"). I will argue that an improved understanding of this mismatch of collapse times will very likely yield insights into other open questions such as the nature of halo assembly bias, the shape of halo density profiles, etc., all of which have a direct phenomenological bearing on problems ranging from direct dark matter detection to understanding the galaxy-dark matter connection. || Physics LH-II || Aseem Paranjape, IUCAA ||
 * 03/03/2015 || **Structure Formation at High and Low redshifts **

We investigate the properties of quasars, galaxies and halos in the cosmological hydrodynamical simulations: MassiveBlack and MassiveBlack-II, which include a self-consistent model for star formation, black hole accretion and associated feedback. We find that baryons affect strongly the halo mass function, with 20-35% change in the halo abundance below the knee of the Mass Function when compared to dark matter only simulations and provide a fitting function for the halo MF out to redshift z=11 and discuss its limitations. The MassiveBlack simulations are able to reproduce a number of observational properties at both high and low redshifts. However we note that to better match observations more efficient AGN feedback (beyond simple thermal coupling used here) is likely necessary for the largest, rarest objects/clusters at low redshifts. || Physics LH-II || Nishikanta Khandai, NISER ||
 * 10/03/2015 || **Extended Heating in the Solar Wind: The Role of MHD Turbulence and Resonance **

<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;">The solar wind is an incredibly well-diagnosed collisionless plasma that exhibits a rich set of plasma physics phenomenology. As such, we can learn valuable lessons about other collisionless or anisotropic plasmas, including accretion onto the galactic center black hole, the intracluster medium of galaxy clusters, and even fusion experiments on earth. In this talk, I will focus on the long-standing problem of understanding the extended heating of the solar wind in the context of energy exchange between particles and waves, a ubiquitous theme in plasma physics. On the analytical side, I will discuss several resonant interactions (cyclotron and transit time damping) and Fermi Type-B interactions and the use of quasilinear theory to describe them. On the numerical side, I will focus on the use of test particle MHD as a numerical tool for studying wave-particle interactions. In particular, I will describe the computational method and highlight some of the fun numerical challenges in its development while highlighting its strengths and weaknesses. Finally, I will connect the analytical and numerical pieces to describe some of our results thus far on the heating of the solar wind. I'll also discuss where these results can be augmented by other computational approaches, such as hybrid methods or gyrokinetics, as well as discuss other possible applications of the test particle MHD method including relativistic particles and accretion disk turbulence. || Physics LH-II || Ian Parrish, CITA ||
 * 17/03/2015 || **<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;">Computation and characteristics of inflationary three-point functions **

<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;">Inflation is currently considered the most promising paradigm to describe the origin of perturbations in the early universe. It is easily achieved using scalar fields, and there exist a plethora of models to drive inflation. Until rather recently, inflationary models were compared with the cosmological data at the level of two-point functions. Over the last decade it has been realized that non-Gaussianities in general and the three-point functions in particular can play a significant role in arriving at stronger constraints on inflationary models. On the one hand, there has been tremendous development on the theoretical front towards the calculation of non-Gaussianities generated during inflation and in post-inflationary scenarios. On the other, the expectation alluded to above has been corroborated to a large extent by the strong constraints that have been arrived at by the Planck mission on the scalar non-Gaussianity parameter. In this talk, after an introduction to the scalar bispectrum and the corresponding non-Gaussianity parameter, I describe our work towards the numerical computation of the inflationary three-point functions (including those involving tensors) and understanding their characteristics (particularly, their behavior in the so-called squeezed limit). || Physics LH-II || L Sriramkumar, IIT Madras ||
 * 28/04/2015 || **<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;">HI Kinematics of the Large Magellanic Cloud revisited : Evidence of possible accretion and out-flow **

<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;">The Large and Small Magellanic Clouds (L&SMC), our nearest neighbors are the two most exciting objects in the Local Group. These gas rich binary systems, interacting with each other and with our Galaxy, are the ideal testbeds in understanding various aspects of galaxy-galaxy interaction and evolution. The gas distribution in the Clouds are expected to bear footprints of the LMC-SMC-MW interaction. Their kinematics is known to be continuously modified by this interaction. The recent proper motion estimates from HST observations re-defined the orbital history of the Clouds. This study re-visits the gas kinematics of the LMC, using atomic neutral Hydrogen (HI) as tracer, in the light of the recent proper motion estimates. The kinematic parameters of the HI disk of the LMC are re-estimated. We observed evidences of possible gas accretion and out-flows in the LMC that are valuable signatures of interaction with its smaller companion, SMC and the MW. We utilized the all sky survey data sets to trace and analyse the gas distribution to a larger extend up to the Magellanic Complexes. || Physics LH-II || Indu G ||
 * 02/06/2015 || **<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;">Measuring the temperature of the high-redshift intergalactic medium **

<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;"> Understanding the thermal evolution of the high-z intergalactic medium (IGM) is of fundamental importance in cosmology. The temperature and density of the IGM are related by an equation of state of the form $T(\Delta) = T_0 (\Delta)^{\gamma - 1}$ where $\Delta$ is the overdensity. Several previous attempts to constrain the parameters ($T_0$ and $\gamma$) of this equation of state involved the fitting of absorption lines in the spectra of quasars, which leads to somewhat large uncertainties. Recent work has pointed to the existence of characteristic values for the overdensities in the high-redshift universe, at which a flux statistic, known as the mean curvature, exhibits a tight correlation with the gas temperature. Using the mean curvature leads to much smaller uncertainties but does not constrain both the parameters of the equation of state. I will describe how the curvature is found to be sensitive to the additional heating effects in the near-zones of high-redshift quasars, which indicate the beginning stages of helium reionization in the universe. I will also describe how the median and percentiles of the curvature are associated with temperatures measured at different characteristic overdensities, and how these can be used together to efficiently constrain both the parameters of the equation of state. The characteristic overdensities are found to have a direct physical interpretation and describe absorbers having sizes of the order of the Jeans' scale in the IGM. This novel approach could help us to accurately constrain the thermal evolution of the high-redshift universe. || Physics LH-II || Hamsa Padmanabhan ||
 * 05/08/2014 || **PARAS (PRL Advanced Radial-velocity Abu-sky Search): The search for Exoplanets**
 * 05/08/2014 || **PARAS (PRL Advanced Radial-velocity Abu-sky Search): The search for Exoplanets**

PARAS is India's first dedicated Exoplanet search program using the Radial-Velocity (RV) technique. The technique measures the Doppler wobble of a star due to the presence of a planet or planets around it. It is the only ground-based indirect method which can give the projected mass (msin(i)) of the planet. Therefore, transit candidates like those from Kepler or others have to be verified using the RV technique for the planet projected mass determination. RV measurements of close to 1m/s are possible using an optical fiber-fed high resolution Echelle spectrograph which is kept under temperature and pressure control. I will discuss the design of the spectrograph, the challenges I met during the making of the spectrograph and share some unprecedented RV precision we obtained on RV standard stars using a 1.2m telescope during the last two years. I will also discuss our new program on the Search for Super Earths using the current 1.2m telescope and the future 2.5m telescope. The new 2.5m telescope is expected to see first light some time in 2019 and will boost the RV precision at sub-1m/s. || Physics LH-II || Abhijit Chakraborty, PRL ||
 * 19/08/2014 || **<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;">Unraveling the evolution of infall, accretion and outflows in protostars: Infrared spectroscopy with Spitzer & Herschel space telescopes **

<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;">Protostars are new born stars and represent the earliest stages of star formation. The protostellar phase is of fundamental importance to star formation as it is during this phase that the final stellar mass is determined and the protoplanetary disks, the birth places of planetary systems, are assembled. Yet, protostellar evolution remains the least understood phase of star formation. The early evolution of protostars is driven by the competition between infall, accretion and outflows, processes that can heat up the surrounding gas to temperatures of several 100 K to several 1000 K. Many of the important cooling lines of the warm and hot circumstellar gas fall in the infrared wavelengths. These lines provide valuable diagnostics of the physical conditions (density & temperature), elemental abundance and spatial extent of the emitting gas, and, thereby offer vital clues on the heating mechanisms. Infrared spectroscopy, thus, is a powerful tool to study the energetic processes that shape protostellar evolution. We have analyzed infrared (5-200 micron) spectra of over 100 protostars from the nearby star forming regions, obtained with the Spitzer and Herschel space telescopes. The protostars in our sample span three orders of magnitude in luminosity and are in various stages of evolution; this is the largest such sample of protostars to date, for which infrared spectra have been obtained and analyzed. I will present our analysis and discuss our main results, which provide new insights into our understanding of the earliest stages of star formation. || Physics LH-II || Manoj Purvankara, TIFR ||
 * 02/09/2014 || **Supernova Explosions: The Role of Exotic Matter**

Supernova explosions are spectacular astronomical events. At the same time, the understanding of the final journey of a massive star after its fuel has been exhausted is a challenging problem. The outcome of it is a core collapse supernova and the residue may take the form of either a neutron star or a black hole. The core collapse supernova explosion mechanism is being investigated over the last five decades. Still, the detailed theory of a successful supernova explosion is beyond our reach. In most core collapse supernova simulations the shock stalls after traversing a few hundred kilometers. It is not yet understood whether dimension of the problem or microphysics such as equation of state of dense matter and neutrino physics is responsible for a successful core collapse supernova explosion.The shock revival by neutrino heating, after hundreds of milliseconds,was investigated in understanding a successful core collapse supernova explosion. On the other hand, novel phases of dense matter such as hyperon, quark or Bose condensates of pions and kaons might be formed just after the bounce of the Fe core. Recently, it was shown that a quark-hadron phase transition might trigger a core-collapse supernova and produce a second neutrino burst. The question is whether other exotic forms of matter such as hyperon matter may lead to such a conclusion or not. Here I discuss our newly constructed hyperon equation of state (EoS) for core-collapse supernova simulations and neutron stars. This is the first supernova EoS involving hyperons which is compatible with the recently measured 2 M⊙ neutron star. Finally I describe the role of hyperon matter on the supernova explosion and neutrino signal. || Physics LH-II || Debades Bandyopadhyay, SINP ||
 * 23/09/2014 || **Clusters of Galaxies: Substructures and Mergers**

I will talk about the results I have obtained during my PhD from an analysis of the dynamics of a sample of 14 clusters of galaxies using their available X-ray and radio observations. The clusters were selected based on the presence of substructures in their optical images and/or interesting radio sources. I have analyzed the radial profiles and 2-D maps of the X-ray surface-brightness and various thermodynamic quantities of these clusters. Many clusters of the sample are found to have anisotropic X-ray morphologies, and X-ray substructures are seen in a majority of the clusters. We have found evidence for the presence of significant large-scale substructures and major mergers in the cluster A3395. Small scale X-ray substructures/multiple X-ray peaks and signs of galaxy scale mergers (evident as small scale high temperature and high entropy regions in the thermodynamic maps) are seen in the central parts of seven of the clusters. The analysis suggested that all but one of the clusters of this sample are non/weak-cool-core clusters. || Physics LH-II || Kiran Lakhchaura, TIFR ||
 * 11/11/2014 || **Modified Einstein's gravity as a missing link between sub- and super-Chandrasekhar type Ia supernovae**

Type Ia supernovae (SNeIa), a key to unravel the evolutionary history of the universe, are believed to be triggered in white dwarfs having mass close to the Chandrasekhar limit. However, observations of several peculiar, under- and over-luminous SNeIa argue for exploding masses widely different from this limit. We show that modification of Einstein's gravity leads to significantly sub- and super-Chandrasekhar limiting masses, determined by a single model parameter. Explosions of these sub- and super-Chandrasekhar limiting mass white dwarfs explain under- and over-luminous SNeIa respectively, thus unifying these two apparently disjoint sub-classes. Our discovery raises two fundamental questions. Is the Chandrasekhar limit unique? Is Einstein's gravity the ultimate theory for understanding astronomical phenomena? Both answers appear to be no! || Physics LH-II || Banibrata Mukhopadhyay, IISc ||
 * 18/11/2014 || **Gamma Ray Bursts: Prospects in radio bands**

Radio observations of Gamma Ray Burst (GRB) afterglows are excellent means to probe the GRB environments and constrain their density nature. Late time radio observations of the GRB afterglow provide most accurate energy estimate independent of the geometry effects. Radio emission also allows us to see important transitions in the afterglow physics, such as synchrotron peak frequency, the cooling break, the trans-relativistic expansion etc., which in turn provide key diagnostics to the fundamental parameters of the explosion. Here I will present a statistical analysis of radio afterglows of GRBs and derive important conclusions and predictions about their properties and detectability. || Physics LH-II || Poonam Chandra, NCRA ||
 * 02/12/2014 || **Studies in Astrochemistry with Herschel Space Observatory**

Astrochemistry is an emerging interdisciplinary subject which has gathered significant momentum during the last decade. Studies in astrochemistry involve analysis of spectroscopic observations of transitions of molecules in space using inputs from (a) laboratory spectroscopy for correct identification of the observed spectral lines and (b) theoretical or experimental estimates of rates of gas-phase and grain-surface chemical reactions. Many of the molecules are naturally found to emit bright spectral lines at wavelengths between 100-2000 GHz. Due atmospheric attenuation, a significant part of this frequency range is inaccessible from the ground-based observatories. Herschel Space Observatory, the most recent far-infrared space mission, with its high resolution spectrometer (operating at frequencies between 480-1250 GHz and 1410-1910 GHz) has provided a unique platform for spectroscopic studies of molecular material in the ISM. In this talk I will present results from absorption line studies using Herschel. || Physics LH-II || Bhaswati Mookerjea, TIFR ||
 * 09/12/2014 ||  || Physics LH-II || Viral Parekh, RRI ||
 * 16/12/2014 ||  || Physics LH-II || Pratyush Pranav ||
 * 21/01/2014 || **Recent star formation in cluster early-type galaxies**
 * 21/01/2014 || **Recent star formation in cluster early-type galaxies**

Unlike the Milky Way Galaxy, some galaxies in the local Universe are observed to be composed of very old, red stars. Popularly called early-type galaxies, these systems are hypothesized to have been fully formed when the Universe was less than half of its current age. Yet, our current understanding of galaxy formation expects galaxies to continue to form and evolve through to the present era. Indeed, the population of early-type galaxies is observed to have increased in stellar mass over the past eight billion years. This talk addresses this apparent contradiction by studying these predominantly old stellar systems in large, dense clusters of galaxies, in search of evidence for recent star-formation episodes. Using images and spectra from the Hubble Space Telescope, ESO's Very Large Telescope in Chile and the W. M. Keck Telescopes in Hawaii, we studied galaxies residing in four clusters at lookback times as far back as seven billion years. Comparing their dynamical and stellar mass estimates to their luminosity, we find that the galaxies in our sample exhibit strong evidence for recent star formation, independent of the epoch at which they are observed. That is, we have found the recent spark of life in these presumably "dead" systems suggesting that their stars were formed over the course of cosmic history, not in a single burst when the Universe was very young. || Physics LH-II || Koshy George, IIA ||
 * 11/02/2014 || **<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;">Recent Studies on Hydrogen-deficient Stars **

<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;"> Unlike normal stars, hydrogen-deficient stars show very little or no hydrogen in their atmospheres. The origin and evolution of these enigmatic stars is not yet clear. In this talk, I will discuss about the observed surface composition of these stars as clues to their origin and evolution. || Physics LH-II || Gajendra Pandey, IIA ||
 * 11/03/2014 || **<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif;">Diffuse neutral interstellar medium: <span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif; line-height: 1.5;">Results and surprises from H I studies **

<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif; font-size: 12.727272033691406px;">The interstellar medium is known to have significant density and velocity structures over a wide range of spatial scales. These structures are generally interpreted as the signature of turbulence in the ISM. In this presentation, I will show some recent results, derived from observations of the Galactic HI, probing the ISM turbulence from parsec to AU scale using several complimentary techniques. In this context, I will discuss, from an observer's point of view, the need of characterizing the nature of the interstellar turbulence to constrain the temperature of the diffuse neutral ISM. Correctly estimating the temperature of the turbulent multiphase ISM is an important issue, particularly in light of the recent observational results that a significant fraction of the gas is in the thermally unstable phase, and that the standard thermal equilibrium may not be entirely correct. || Physics LH-II || Nirupam Roy, Max Planck Institute for Radio Astronomy, Bonn ||
 * 18/03/2014 || **<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif; font-size: 12.727272033691406px;">Understanding early Solar System processes using isotope geochemistry **

<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif; font-size: 12.727272033691406px;">Variations in the isotopic composition of terrestrial and meteorite samples are well documented. Such variations are typically explained by fractionation and incomplete mixing in the Solar Nebula prior to accretion, late injection of pre-solar material and its inhomogeneous distribution, decay of extinct radionuclides, planetary differentiation, etc. In this talk, I'll provide some examples of such isotopic variations which has implications for early Solar System processes. || Physics LH-II || Ramananda Chakrabarti, IISc || <span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif; font-size: 12.727272033691406px;"> A physical mechanism that can excite the coherent radio emission in pulsars is still a challenging problem in astrophysics, even after 45 years of pulsar discovery. In all models of pulsar radio emission there is general agreement that the radio emission arises due to growth of plasma instabilities in the relativistic electron positron plasma streaming along open dipolar magnetic field. Currently a wealth of high quality observations exist, which over the years have been instrumental in putting stringent constraints to pulsar coherent radio emission models. In this talk we will discuss the observational results that strongly suggests that the pulsar radio emission is excited by coherent curvature radiation. The physical process include formation of an inner acceleration region close to the neutron star surface where magnetic pair creation forms primary plasma with lorentz factors of 10^6 followed by secondary plasma with lorentz factor of about few times 10^2 due to a non-stationary sparking process. For this process to work, highly non-dipolar surface magnetic ﬁeld is essential. Then, further in the radio emission region, plasma instabilities in the secondary plasma leads to the coherent curvature radiation via multi-step process exciting extraordinary (X) and ordinary (O) modes of in the plasma. This talk will also focus on the work we are doing to unravel this physical process. I will also mention issues that remain to be resolved. || Physics LH-II || Dipanjan Mitra, NCRA || Abstract : Sub-stellar Mass Objects (SMO) are astrophysical objects that lack sufficient mass to become a star. Brown dwarfs and planets belong to this class of objects. The physics of SMO begins from their formation mechanism which for brown dwarfs, is similar to that of stars. While brown dwarfs are formed out of the core collapse of massive interstellar cloud, planets are formed by continuous accumulation of matter during the initial stage of star formation. In recent years a large number of planets outside the solar system is discovered. The mass range of brown dwarfs and giant extra-solar planets overlaps making it impossible to distinguish them from each other. In the present talk, I shall discuss the basic physical and chemical properties of these objects as derived from astronomical observation. || Physics Lecture Hall - II || Sujan Sengupta (IIA) || Abstract: The standard scenario of outflows from galaxies has been that of gas driven by thermal pressure of the interstellar medium which is heated by supernovae. Recent observations of galactic outflows have shown that radiation pressure may also be of importance. We will discuss a few issues regarding the physical mechanism behind these outflows and the implications for the evolution of galaxies and the intergalactic medium. || Physics Lecture Hall - II || Biman Nath (RRI) || Abstract: The diffuse radiation field extends over the entire spectral range from gamma rays to the radio with different sources in different bands. I will present our new results on the ultraviolet sky based on observations from Voyager, FUSE, and GALEX. These have greatly complicated our understanding of the origin of the ultraviolet radiation field with implications for the extragalactic radiation field; the structure of our own Milky Way with the reprocessing of the starlight; and the dust in the Solar System. For the first time, our data are much better than our models. || Physics Lecture Hall - II || Jayant Murthy (IIA) || Abstract: The Large and the Small Magellanic Clouds are two neighbouring galaxies believed to be orbiting our Milky Way. The formation of Magellanic Stream and Magellanic Bridge, connecting the Clouds are expected to be formed due to their mutual interaction and their interaction with our Galaxy. These two galaxies are chemically undernourished and hence the stellar properties and the evolution of stars are expected to be different in these galaxies. Recent studies using various observational facilities in the southern hemisphere have altered several assumptions we had about these two Clouds. I shall summarise my endeavour to understand the stellar population, structure of various components like the bar, disk and halo of these two neighbours. || Physics Lecture Hall - II || Annapurni Subramaniam (IIA) || Abstract: Low Luminosity spiral galaxies are generally dark matter dominated systems that that have extended gas disks but show little star formation. They are thus poorly evolved galaxies and do not show much nuclear activity. However, recent studies have shown that a significant fraction do have active galactic nuclei (AGN) that are associated with low mass nuclear black holes. In some cases radio lobes or jets have also been observed. This presentation will focus on observational studies of the nuclear activity of such galaxies and its implications for studies of galaxy evolution. || Physics Lecture Hall - II || Mousumi Das (IIA) || Abstract: We establish the equation of motion of pseudoscalar particles coupled to an electromagnetic field in a classical gravitational background through the use of conformal time and flat geometry. We show that the expansion of the universe can lead to larger mixing than in a stationary universe. We also show that for a broad range of parameters, one can obtain resonance in mixing, i.e, a region where the mixingbecomes maximum. || Physics Lecture Hall - II || Subhayan Mandal (University of Liege, Belgium) || There are magnetic waves in the corona with many different "wiggling periods," or frequencies. These waves are responsible for the coronal heating and solar wind acceleration. In this talk I will review the current status on the detection of these waves and current understanding on the mode physics. || Physics Lecture Hall - II || Dipankar Banerjee (IIA) || TeV blazar Mrk421 was found to undergo one of its brightest flaring episodes on 17 February, 2010 by various experiments in X-rays and gamma-rays. A multiwavelength (Radio to gamma-rays) study of this high state of the source is carried out to understand the most basic questions about the AGN jets, such as what the jets are made of and how matter is accelerated in the jets. Our study suggests that flares during 16 and 17 February, 2010 could arise due to a passing shock in the jet. I will also present results from other AGN's detected by HAGAR telescope. || Physics Lecture Hall - II || Amit Shukla (IIA) || Till around few years back, cosmological results from galaxy cluster surveys were dominated by statistical uncertainties. However, with sample size from a single survey getting progressively larger, constraints are now dominated by systematics. This has led to a complete change in outlook and strategies with which current and upcoming cluster surveys are being executed or planned. Once systematics are suitably controlled, these surveys have formidable cosmological power compared to any other cosmological probes. In this talk, I will give a quick tour of cluster surveys, from Optical and IR to sub-mm and X-Rays, and will point out recent results and future prospects. || Physics Lecture Hall - II || Subhabrata Majumdar (TIFR) ||
 * 15/04/2014 || **<span style="background-color: #ffffff; color: #222222; font-family: arial,sans-serif; font-size: 12.727272033691406px;">On the nature of coherent radio emission from pulsars **
 * 12/7/2011; 4pm || **Rapid X-ray variability of black hole systems** || Physics Lecture Hall - II || Ranjeev Misra (IUCAA) ||
 * 26/7/2011; 4pm || **Physics and Astrophysics of Sub-stellar Mass Objects**
 * 26/7/2011; 4pm || **Physics and Astrophysics of Sub-stellar Mass Objects**
 * 9/8/2011; 4pm || **Galactic outflows with radiation pressure**
 * 23/8/2011; 4pm || **The Diffuse Ultraviolet Sky: A New View on an old Problem**
 * 20/9/2011; 4pm || **Understanding our neighbours - The Magellanic Clouds**
 * 2**7**/9/2011; 4pm || **Nuclear Activity in Low Luminosity Spiral Galaxies**
 * 4/10/2011; 4pm || **Probing Cosmic Magnetic Fields using CMB** || Physics Lecture Hall - II || T. R. Seshadri (Univ of Delhi) ||
 * 18/10/2011; 4pm || **\chi - \gamma mixing in an expanding universe**
 * 15/11/2011; 4pm || **Magnetic Waves in the Solar Atmosphere**
 * 7/2/2012; 4pm || **Multiwavelength study of TeV Blazar Mrk421 during giant flare**
 * 7/2/2012; 4pm || **Multiwavelength study of TeV Blazar Mrk421 during giant flare**
 * 21/2/2012; 4pm || **A New Age of Cluster Surveys for Cosmology**
 * 3/4/2012; 4pm || **Ultra High Energy Cosmic Rays from Mildly Relativistic Supernovae**

The origin of the Ultra High Energy Cosmic Rays (UHECRs) remains an enigma. Interaction with the CMB severely suppress the flux of protons and nuclei from distant sources, at energies above the Greisen-Zatsepin-Kuzmin (GZK) limit. A local sub-population of type Ibc supernovae with mildly relativistic ejecta have been detected for some time as sub-energetic GRBs or X-Ray Flashes and more recently as radio afterglows without detected GRB counterparts, such as SN 2009bb. In this talk we shall discuss the measurements of SN 2009bb using its radio spectra obtained with the VLA and GMRT. This will allow us to see where the engine-driven SNe lie on the Hillas diagram and whether they can explain the post-GZK UHECRs? || Physics Lecture Hall - II || Sayan Chakraborti (TIFR) ||
 * 17/4/2012; 4pm || **Cold gas at high redshift**

I will discuss the evolution of the temperature distribution of gas in damped Lyman-$\alpha$ systems (DLAs), based on our recent GMRT and GBT HI 21cm absorption studies of a large sample of DLAs and strong MgII absorbers at $0.1 < z < 3.4$. We find that most of the HI in high-$z$ ($z > 2$) DLAs is in the warm phase, with high spin temperatures ($T_s \gtrsim 1000$~K). The detection rate of HI 21cm absorption is found to increase with decreasing redshift, with a low detection rate in $z > 2$ absorbers. The detection rate at $z \sim 1$ is similar to that in low-z DLAs, implying that normal galaxies contain significant fractions of cold HI by $z \sim 1$. I will also present new evidence for an anti-correlation between spin temperature and metallicity [Zn/H], which indicates that metallicity is the primary factor in determining the temperature distribution in the interstellar medium. Finally, I will describe recent GMRT and WSRT HI 21cm absorption studies of neutral gas in the Galaxy, which find evidence for an HI column density threshold for cold gas formation, apparently due to self-shielding against the penetration of ultraviolet photons into neutral hydrogen clouds. || Physics Lecture Hall - II || Nissim Kanekar (NCRA) ||
 * 24/4/2012; 4pm || **Snapshots of Infall, Merger and Feedback processes driving galaxy evolution**

The physical processes that drive galaxies to evolve is very complex. Observations at various wavelengths ranging from X-ray to radio are needed to trace various components of the galaxy and then infer the evolutionary sequence. I will describe detailed case studies of a few galaxies, best-targets for a specific physical process. Since some processes are significant but are of very short time-scale, exampler galaxies are often rare. To explain certain evolutionary scenarios appropriate galaxies are also missing in the current literature and we aim at discovering such missing-link galaxies. I will present analysis and discovery of a few 'fireball galaxies', first time falling into a cluster with UV-bright knots of young star formation spreading up to 90 kpc in the trail. Gas infall from cosmic filaments to clusters of galaxies can also be traced by diffuse radio plasma. I will describe our discovery of the exotic radio galaxy 'Speca'. This is only the second spiral-host radio galaxy and the second triple double episodic radio galaxy. The diffuse plasma from its oldest jet episode is not steep but has flat spectrum, possibly re-accelerated by the Mpc-scale accretion shock onto a newly forming cluster at z~0.2. In the process of growth by merger and regulation by feedback processes, NGC3801 is a unique target. We seem to have caught it in the act of changing from a post-merger star forming early-type galaxy phase to a red-and-dead elliptical-like galaxy via wind-driven fast gas-loss and jet-driven shock shells seen in X-rays. || Physics Lecture Hall - II || Ananda Hota ||
 * 15/5/2012; 4pm || **Neutrinos: in physics and astrophysics**

I'll briefly review the neutrino story from Pauli's letter of 4th December 1930, to the very recent results of Daya Bay, from China, and to RENO, from Korea. || Physics Lecture Hall - II || D. V. Ahluwalia (Univ. of Canterbury) ||
 * 21/8/2012 || **Magnetic field generation due to turbulence in linear shear flows**
 * 21/8/2012 || **Magnetic field generation due to turbulence in linear shear flows**

Large-scale cosmic magnetic fields are believed to originate from dynamo action in the electrically conducting fluids. The framework of mean-field electro-hydrodynamics, which has been developed/evolved by using Maxwell's equations together with Ohm's law during the past few decades, aims to address some of the outstanding puzzles related to magnetic fields in the universe. One particular challenge is to explain the generation of magnetic fields over length scales exceeding the length scale of turbulence. In this talk, I will try to discuss the Galilean invariant formulation together with some recent numerical simulations concerning the shear dynamo problem, where the aim would be to understand the Galilean invariant formulation together with some recent numerical simulations concerning the shear dynamo problem, where the aim would be to understand the following question : under what conditions does the equation for mean (ordered) magnetic field admit growing solutions due to non-helical turbulence in a background linear shear flow? || Physics Lecture Hall - II || Nishant Singh (RRI) ||
 * 4/9/2012 || **Energy Deposition Profiles and Entropy in Galaxy Clusters**

I will talk about the fractional entropy enhancement in the intra-cluster medium (ICM) of the clusters using their observed entropy profiles from the REXCESS survey. We have made an estimate of the non-gravitational energy for these clusters in the central regions and outside the core. The relation of the non-gravitational energy with the mass of the cluster and its trend with the central radio luminosity support models of AGN feedback in these clusters. || Physics Lecture Hall - II || Anya Chaudhuri (TIFR) ||
 * 11/9/2012 || **Nucleosynthesis inside GRB Accretion Disks and Associated Outflows**

Most popular models of long duration gamma-ray bursts invoke the core collapse of rapidly rotating stars. The mass of the stars undergoing core collapse is usually greater than 20M<span style="font-family: DejaVu Sans Mono,monospace;">ʘ in the main sequence. This core collapse results in the formation of black holes of 2-3 M<span style="font-family: DejaVu Sans Mono,monospace;">ʘ if it is of Schwarzschild type and 6-7 Mʘ if it is of maximally spinning Kerr type with an accretion disk around them. Such black holes accrete at the rate of 0.001-10.0 Mʘs-1. We investigate nucleosynthesis inside such gamma-ray burst accretion disks with accretion rate upto 0.1 Mʘs-1 since these disks are more likely to synthesize heavy elements. We show that varying accretion rate changes the nucleosynthesis products. We also report how nucleosynthesis is sensitive to the variation of the initial abundance of elements in the accretion disk, namely whether it is Si rich or He rich. In addition to the formation of various isotopes of Fe, Co and Ni we report the synthesis of new elements like Ar35, F21, Mn53 and various isotopes of Cr which have not been reported earlier. Next, we investigate whether these elements survive in the outflows from the disk and we find that the result is sensitive to the fraction of mass ejected to the mass accreted and hence to the velocity of ejection. When the velocity of ejection is small we find that many new elements like isotopes of Ti, V and Cu are also synthesized. Many of these elements have been observed in the X-ray afterglows of several gamma-ray bursts. || Physics Lecture Hall - II || Indrani Banerjee (IISc) || Interstellar medium is observed to have a hierarchy of structures across a large range of length scales. Statistical properties, like power spectrum, structure function or correlation function provide ways to quantify these scale invariant structures and probably can help us understand about their generating mechanisms. It has been found that the slope of the power spectrum of these fluctuations is similar across the length scales ranging from AU to kilo parsecs. Probably, this indicates a single physical process behind the generation of these structures. Resent results on this will be discussed. || Physics Lecture Hall - II || Prasun Dutta (NCRA) ||
 * 18/9/2012 || **Probing Interstellar Medium at different scales**
 * 25/9/2012 || SMOOTHED PARTICLE HYDRODYNAMICS IN THE CONTEXT OF UNDERSTANDING THE FORMATION OF STARS

Techniques in computational fluid dynamics, in recent years, have seen stupendous rise in applications to numerous astrophysical problems. Both grid-based as well as particle-based schemes have been exploited for the purpose. In this talk, I propose to introduce the particle-based Smoothed Particle hydrodynamics algorithm and discuss its success in improving our understanding of the formation of stars. The problem has two aspects : (i) the dynamical processes responsible to trigger the epidemic of star-formation, and (ii) the birth of stars within a sufficiently dense volume of gas, better known as the prestellar core. The present status of the theory will be reviewed. || Physics Lecture Hall - II || Sumedh Anathpindika (IIA) ||
 * 16/10/2012 || **The magnetic Earth: observations and models**

There is evidence that the Earth had a dipolar magnetic field as early as 3.5 billion years ago. Observations of the Earth's magnetic field on the surface reveal its highly dynamic nature. In this talk I shall present some of the main features of the Earth's field, such as time variations and polarity reversals. I also discuss how fluid dynamo models have improved our understanding of the Earth's deep interior. || Physics Lecture Hall - II || Binod Sreenivasan (IISc) ||
 * 30/10/2012 || **Gyro-orbit size, brightness temperature limit and implausibility of coherent emission by bunching in synchrotron radio sources**

We show that an upper limit on the maximum brightness temperature for a self-absorbed incoherent synchrotron radio source is obtained from the size of its gyro orbits. For radio variables, the intra-day variability (IDV) implies brightness temperatures 10^{19} K in the co- moving rest frame of the source. This, if interpreted purely due to an incoherent synchrotron emission, would imply gyro radii >10^{28} cm, the size of the universe, while from the causality arguments the inferred maximum size of the source in such a case is 10^{15} cm.

Such high brightness temperatures are sometimes modeled in the literature as some coherent emission process where bunches of non-thermal particles are somehow formed that radiate in phase. We show that, unlike in case of curvature radiation models proposed in pulsars, in the synchrotron radiation mechanism the oppositely charged particles would contribute together to the coherent phenomenon without the need to form separate bunches of the opposite charges.

At the same time we also show that due to a subtle effect, bunches would disperse over dimensions larger than a wavelength in time shorter than the gyro orbital period 0.1 sec. Therefore a coherent emission by bunches cannot be a plausible explanation of the high brightness temperatures inferred in extragalactic radio sources showing variability over a few hours or longer, thereby ruling out a whole class of models that have been proposed in the literature. || Physics Lecture Hall - II || Ashok Singal (PRL) ||
 * 27/11/2012 || **Clumpy Structures and Violent Disk Instability at Early Epochs of Galaxy Formation**

Clumpy galaxies are a unique population at high redshifts. They host individual star-forming clumps that are orders of magnitude more massive and denser compared to the starbursts seen in the local Universe. Whether these clumps are embedded in an underlying disk with significant rotation or not, is unclear as yet. However, their kinematics clearly reveal that these are dispersion-dominated systems. One of the major challenges is to understand how the clumpy galaxies have evolved into the relatively smooth bulge and disk structures seen in the present-day galaxies. Theoretically, the massive clumps seen at high redshifts are thought to be the result of violent disk instability in the gas-rich, turbulent galaxy disks. Their dynamical evolution happens on timescales much shorter compared to secular processes. Hydrodynamical simulations have attempted to understand the formation and evolution of clumps at spatial resolutions comparable to the current observational data. The basic picture involves fragmentation, clump formation and migration to the central regions, resulting in a bulge component if the clumps manage to survive disruption. In this talk, I will present some of the recent observations of clumpy galaxies, and compare the properties of the star-forming clumps to the basic predictions from the theory of violent disk instability, clump formation and migration. || Physics Lecture Hall - II || Swara Ravindranath (IUCAA) ||
 * 11/12/2012 || ==** Propagating intensity disturbances: Slow mode waves? or Recurring upflows? **==

Quasi-periodic propagating disturbances were first observed in the polar plumes followed by similar observations in the active region fan loops in the solar corona. They were almost universally interpreted as signatures of slow-mode magneto-acoustic waves for more than a decade. Although, the slow mode waves solely can not supply sufficient energy to power the solar wind or to heat the corona, ample amount of observations coupled with theoretical modeling, resulted in several seismological applications. But the recent spectroscopic observations question the uniqueness of the interpretation of these propagating disturbances. The main argument is that the high speed recurring upflows can also produce similar signatures and it is more likely that a significant fraction of the previous observations confirm to these upflows rather than to the slow mode waves. All the observed properties cannot be explained by either of these interpretations due to many limitations, but some of them may help to clearly distinguish the waves from flows which will be discussed. || Physics Lecture Hall - II || Krishna Prasad (IIA) || (Note the unusual day) || **Magnetic fields in our Milky Way Galaxy and nearby galaxies**
 * 14/01/2013
 * 14/01/2013

Magnetic fields in our Galaxy and nearby galaxies have been revealed by starlight polarization, the polarized emission of dusts and clouds at millimeter and submillimeter wave-length, the Zeeman effect of spectral lines or maser line from clouds or clumps, the diffuse radio synchrotron emission from relativistic electrons in the interstellar magnetic fields, the Faraday rotation of background radio sources. It is relatively easier to get a global picture for magnetic fields in nearby galaxies than our Milky Way, while we have measured much more details of magnetic fields in our Milky Way, especially the great results from pulsar rotation measure data. In general, magnetic fields in spiral galaxies probably have a large-scale structure. The fields follow the spiral arms with or without the field direction reversals. In the halo of spiral galaxies magnetic fields exist and probably also have a large scale structure as toroidal and poloidal fields, but seems to be weaker than those in the disk. In the central region of some galaxies, poloidal fields have been detected as X-shape structure. Magnetic field directions seem to have been well preserved during cloud formation and star formation, from large-scale diffuse interstellar medium to molecular clouds to the cloud cores of star formation region or clumps for the maser spots. In general magnetic fields in galaxies are passive to dynamics. || Physics Lecture Hall - II || JinLin Han (National Astronomical Observatories, Chinese Academy of Sciences) ||
 * 22/01/2013 || **MHD of accretion mounds on Neutron stars**

In accreting neutron star binaries, accreted matter is chanelled to the poles of neutron stars forming an accretion mound. We model such mounds by numerically solving the Grad-Shafranov equation for axisymmetric static MHD equilibria. From our solutions we infer local distortion of field lines from initial dipolar structure due to the weight of accreted matter. We study the stability of such mounds by performing MHD simulations using the PLUTO MHD code. We find that pressure and gravity driven modes disrupt the equilibria of the confined accretion mound for heights larger than a threshold. MHD instabilities influence cross field transport of matter as it spreads on the neutron star surface, affecting the efficiency of the screening effects of the spreading matter. We also explore the possible implications of such local field distortions on the cyclotron spectra seen in X-ray emissions from such mounds. || Physics Lecture Hall - II || Dipanjan Mukherjee (IUCAA) ||
 * 29/01/2013 || **Star formation and feedback in the faintest dwarf galaxies**

In the Lambda-CDM universe we are thought to inhabit, cosmic structure is believed to have evolved hierarchically. Smaller dark matter halos coalesced together to form larger halos, which host the large galaxies like our Milky Way. Nearby star forming dwarf galaxies are the closest analogues we have to the first small galaxies that form. It is thought that our limitations in understanding star formation and feedback processes in the smallest galaxies are the reasons for the outstanding problems between simulations of structure formation and observations: the 'core-cusp' problem and the 'missing satellites' problem. Hence it is imperative to observe these small systems and test our understanding of star formation and feedback in these relatively simple systems. We have used data from the largest survey of nearby faint dwarf galaxies in neutral hydrogen (HI), the Faint Irregular Galaxy GMRT Survey (FIGGS), in conjunction with multi-wavelength ultraviolet, optical and infrared data, for our studies. We have investigated the relationship between neutral hydrogen and star formation in these galaxies, at both global as well as local scales. We have also looked at signs of feedback from star formation into the ISM of these galaxies, in the form of the existence of the radio-FIR correlation for these galaxies, and signature of HI outflows in the smallest starburst galaxies. I will talk about the results obtained from the above mentioned investigations. || Physics Lecture Hall - II || Sambit Roychowdhury (NCRA) ||
 * 05/02/2013 || **First stars and the Chemical evolution of the early Galaxy**

One of the open problems of modern cosmology is to understand the nature of the first objects formed in the universe. Until the availability of next generation space telescopes, it is not possible to observe these first objects directly. However the first low mass stars of the Milkyway Galaxy and the local dwarf satellites are still be observable in a greater detail, by the current observing facilities. These low mass stars carry the imprints of the first Supernovae. Currently the lowest metallicity system observable in the Universe are these low mass Milkyway metal poor stars. These extreme metal poor (EMP)([Fe/H] $<$ -2.5) stars were formed at early epochs, when the ISM was polluted only by the first generation of supernovae. The chemical abundances of key elements observed in these stars are sensitive to the masses of the early Supernovae. The chemical feed back of the SN will be used to probe the IMF the Pop-III stars. Near field cosmology is complementary to high redshift SN, GRB and IGM studies. Here we present some recent results exploring the origin of carbon in the early galaxy, based on full kinamatics and carbon abundances using large sample of SDSS spectra. || Physics Lecture Hall - II || Sivarani Thirupathi (IIA) ||
 * 05/03/2013 || **The Challenges of observing 21 cm emission from the Epoch Of Reionisation**

The epoch of reionisation (EoR) is an important phase transition in the early universe, in which the first stars and quasars formed due to the collapse of structures in the early universe reionised the universe. Measurement of the spatial distribution of neutral hydrogen via the redshifted 21 cm line promises to revolutionize our knowledge of the epoch of reionization and the first stars and quasars formed in the universe. In my talk I will give an observers view of the existing theoretical models of this epoch and the challenges of observing signatures of EoR hidden in the foreground emission from other celestial sources, which are five orders of magnitude brighter. Imaging techniques developed for the large low-frequency radio arrays that are being built to detect EoR statistically and also small-scale projects planned by several groups to measure a possible global spectral feature will be described in the talk, emphasizing the ongoing work at RRI. In the next decade or so the Square Kilometer Array (SKA) will be the world's largest and the most sensitive radio telescope. Whereas all precursors/pathfinders aim to study the EoR signal statistically through its power spectrum, SKA will be able to image the neutral hydrogen distribution directly and its focus will therefore be more on tomography. The talk will also briefly discuss the possible astrophysical impacts of the planned SKA studies. || Physics Lecture Hall - II || N. Udayashankar (RRI) ||
 * 19/03/2013 || **Cosmic Reionization: Probing Galaxy Formation and Constraining Cosmological Parameters**

Cosmic reionization is a process whereby hydrogen (and helium) in the Universe is ionized by the radiation from stars and other sources. The study of reionization is of immense importance since (i) it is directly related to the formation of first galaxies and (ii) the detailed history of reionization can affect the determination of cosmological parameters. Research in this area received a big boost due to availability of a variety of observational data accumulated over the past few years with additional progress expected soon from a number of different ground-based and space-borne experiments. In this talk, we will review our understanding of the physical processes related to reionization and then present our recent results on data-constrained reionization scenarios and cosmological parameters. We will also discuss prospects for determining the reionization history of the Universe using future observational probes. || Physics Lecture Hall - II || Tirthankar Roy Choudhury (NCRA) ||
 * 26/03/2013 ||  || Physics Lecture Hall - II || Banibrata Mukhopadhyay (IISc) ||
 * 02/04/2013 || **Prompt emission of GRBs**

Gamma-ray bursts (GRBs) were discovered in late 1960's as flashes of gamma-rays and hard Xrays, known as the prompt phase. Later they were observed throughout the electromagentic spectrum as afterglows. The precise localization of GRBs proved their cosmic origin, which together with high observed flux, placed GRBs as the most energetic events in the universe. More than a dozen satellites have been flown (e.g., Swift, Fermi), numerous afterglow and host galaxy studies have been carried out to identify the physical mechanism of GRBs. These have given a phenomenological perspective regarding the origin of GRBs. From these extensive studies we know that GRBs have two classes. Type I GRBs are formed by merging of binary compact objects, while Type II GRBs are formed due to collapse of very massive Wolf-Rayet (WR) stars. In spite of these discoveries the central engine and the emission mechanism of the prompt phase of GRBs remain a puzzle. These are addressed from a data analysts point of view, using the set of Type II GRBs, which have certain advantages over Type I --- (i) larger set, (ii) longer prompt phase, (iii) brighter afterglow phase. I shall argue that meaningful physical pictures can be identified by closely examining the temporal structures and studying the spectral evolution, rather than analyzing the average spectrum. I shall show that some reasonable assumptions of the spectral evolution can lead to correct identification of the underlying radiation mechanism. This formalism has led to some very recent and tantalizing results like improvement of the GRB luminosity indicator, explanation of very high energy (GeV) emission. || Physics Lecture Hall - II || Rupal Basak (TIFR, Mumbai) ||
 * 16/04/2013 || ** Heating and Dynamics of Solar Atmopshere **

The problem of solar coronal heating and different dynamic phenomena seen in the corona has posed great challenges so the solar physics community. Magnetically dominated solar atmosphere consists of a verity of features such active regions, coronal loops, bright points etc. Therefore, understanding the physics of different kinds of structures are the key to understanding the heating and dynamics. The recent observations from Hinode, and Solar Dynamics Observatory have presented us with unprecedented observations helping us to measure physical quantities in the solar corona and study the dynamics. In this talk, the speaker will present some of the recent observational results and their implications on heating and dynamics of solar atmosphere. || Physics Lecture Hall - II || Durgesh Tripathi (IUCAA) ||
 * 30/04/2013 || **Building X-ray Telescopes**

X-ray telescopes are now a critical component of our study of astrophysical sources. Hard X-ray telescopes operating in the energy range from about 10 -- 100 keV provide a unique window into the physics of extreme environments around compact objects at all scales. Functionally, hard X-ray telescopes are very different from optical or X-ray telescopes. In this talk, I will discuss the construction, working and calibration of hard X-ray telescopes. I will present examples from calibrations of NASA's recently launched NuSTAR (www.nustar.caltech.edu) and upcoming the CZT Imager on board India's Astrosat. || Physics Lecture Hall - II || Varun Bhalerao (IUCAA) ||
 * 28/05/2013 || **Study of Astrophysical Sources in Very High Energy Regime Using Ground Based Gamma-ray and Neutrino Telescopes**

In this presentation I will talk about sources like pulsars, AGN and GRBs in very high energy regime. At these energies we study non-themal Universe. From observations we know that relativistic effects are taking place inside these objects. These sources emit high energy gamma-rays and are also expected to emit neutrinos. I will explain detection principle of gamma-rays and neutrinos with earth based detectors. I will also discuss some important observations for the above mentioned sources with ground based Cherenkov telescopes and IceCube neutrino observatory. || Physics Lecture Hall-II || Debanjan Bose (Vrije Universiteit Brussel,Belgium) ||
 * 30/07/2013 || **Ignition and launching the galactic winds**
 * 30/07/2013 || **Ignition and launching the galactic winds**

Galactic wind -- one of the most spectacular phenomena in astrophysics -- is experienced by nearly every one of ten galaxies. In spite of a 50 years long history the energy sources and driving mechanisms supporting galactic winds are still under a voile: even though it looks obvious that in most cases the energy is provided by stellar activity, it is far from being clear how this energy converts into a collimated mass outflow, what is the conversion efficiency and how it depends on the underlying stellar population. I briefly outline the overall picture and then turn to discuss recent results reached in theoretical considerations of the two driving mechanisms: supernovae explosions and stellar radiation pressure. I emphasize that in spite of certain achievements in understanding characteristics of outflows on large scales, the main questions relevant to the central (driving) engine and to the very initial stages of wind evolution remain unanswered. || Physics LH-II || Yuri Shchekinov, Southern Federal University, Russia ||
 * 06/08/2013 || **Towards the complete picture of radio galaxy physics: theory vs. observations**

Radio Galaxies are the potential laboratories for studying the jet black hole symbiosis in extragalactic black hole accretion system. In this seminar, I will give an overall picture of radio galaxy physics including our recent results. In our recent work, our theoretical and observational study of jet and its dynamics in different episodes of jet activity has revealed various hitherto unknown aspects of the extragalactic jets. We discover that the injection spectral indices are similar in the two different episodes for most of the Episodic Radio Galaxies in our sample. I will discuss the implications of this results in building a self-consistent theoretical picture of the dynamics of FRII jets and the particle acceleration (Fermi first order) physics at the jet termination shocks. || Physics Lecture Hall-II || Chiranjib Konar, ASIAA, Taiwan ||
 * 13/08/2013 || **Star formation efficiency at high redshift and sub-galactic scales**

Massive galaxies in the distant Universe form stars at much higher rates than today. Although direct resolution of the star forming regions of these galaxies is still a challenge, recent molecular gas observations at the IRAM Plateau de Bure interferometer enable us to study the star formation efficiency at sub-galactic scales around redshift z = 1.2. We present a method to obtain the gas and star formation rate (SFR) surface densities of ensembles of clumps composing galaxies at this redshift, even though the corresponding scales are not resolved. This method is based on the identification of these structures in position-velocity diagrams corresponding to slices within the galaxies. We use unique IRAM observations of the CO(3-2) rotational line and DEEP2 spectra of four massive star forming distant galaxies to determine the gas and SFR surface densities of the identifiable ensembles of clumps that constitute them, and derive a spatially resolved Kennicutt-Schmidt (KS) relation at a scale of about 8 kpc. The data globally indicates an average depletion time of 1.9 Gyr, but with significant variations from point to point within the galaxies. || Physics LH-II || Jonathan Freundlich, Observatoire de Paris, France ||
 * 20/08/2013 || **Binary Radio Pulsars: Prospects and Problems**

Depending upon values of different parameters, neutron stars can be visible as radio pulsars. Radio pulsars can be either isolated or binary; and a binary pulsar can have either a white dwarf or another neutron star or a back hole as its companion. Binary radio pulsars are used as probes to fundamental theories of physics, including properties of ultra dense matter, gravitation, evolution of massive stars, etc. In this talk, I will describe some of these aspects. First, I will explain the potential of constraining the equation of state for dense matter from measurements of post-Keplerian orbital parameters of neutron star-neutron star binaries. Here I will briefly touch some probable difficulties to model such parameters for neutron star-black hole binaries (after the first discovery is made). Then I will come to binary evolution and effects of stellar interactions in globular clusters and the need of improved population synthesis studies for binary radio pulsars. I will also discuss the difficulty to detect these objects due to the degradation of the flux as a result of their orbital accelerations and methods to overcome this difficulty. Afterwards, I will briefly describe the international effort to detect gravitational waves using radio pulsar data. I will also address the need of searching for new pulsars. || Physics LH-II || Manjari Bagchi, ICTS-TIFR ||
 * 27/08/2013 || **Primordial Magnetic Fields & Early Structure Formation In The Universe**

From previous studies it is known that the presence of primordial magnetic fields during pre-recombination era could generate extra matter perturbations (over and above inflationary matter perturbations) in the universe, this contributes to matter power spectrum appreciably as an additional power at smaller scales (k ~ 1 -10 h/Mpc). Moreover presence of sufficiently strong magnetic fields can lead to heating of the ambient medium due to decaying turbulence and ambipolar diffusion, and therefore affect the structure formation as thermal history plays a crucial role in this processes. Thus we see that the presence of primordial magnetic fields can have several implications for structure formation, and therefore, in turn, for the matter distribution in the universe. A careful analysis of the various cosmological observables which essentially probe the matter distribution in the universe e.g. CMBR (Cosmic Microwave Background Radiation), weak lensing, Ly-alpha forests etc, can actually probe the existence of primordial magnetic fields also. In this talk I will present some of our results about how can primordial magnetic field affect the structure formation in the Universe and how we can constrain the primordial magnetic field parameters, using weak lensing and Ly-alpha observables. || Physics LH-II || Kanhaiya Pandey, RRI ||
 * 10/09/2013 || **Clues about Jet Propagation and Emission from a Multi-wavelength Study of MOJAVE* Blazars**

I will present the results of our recent and ongoing work on the deep radio (VLA), optical (HST) and X-ray (Chandra) imaging of blazar jets belonging to the MOJAVE sample. VLA imaging has revealed that blazar jets often have complex structures. Many of them are bent, show multiple hot spots and cannot be easily placed into the two primary Fanaroff-Riley categories. Multi-epoch monitoring with the VLBA has produced a comprehensive database of individual jet component speeds on parsec-scales. We have found a close link between the jet speeds on parsec-scales and the radio lobe emission on kiloparsec-scales. Deep Chandra and HST observations of jets in selected MOJAVE blazars have indicated that the X-rays are produced via the inverse-Compton over CMB photon (IC/CMB) mechanism. I will finally discuss the preliminary findings from our currently ongoing investigation of 3 blazars that exhibit a hybrid radio morphology.

LH-II || Preeti Kharb, IIA ||
 * MOJAVE = Monitoring of Jets in AGN with VLBA Experiments || Physics
 * 08/10/2013 || **Galactic Outflows**

Galactic outflows are multiphase hydrodynamic phenomena observed in various wavelengths. In this talk, I will discuss the outflows driven by the galactic radiation, ram pressure, supernovae and AGN. I will describe the dynamics of clumpy outflows acted upon by radiation from galaxy and the ram pressure due to hot phase of outflow, which can explain the criteria for existence of outflows and also the observed threshold of winds. I will then present a hydrodynamic steady wind model for supernovae and AGN driven outflows, where we find that if the AGN powers the outflow then the speed should be greater than 1000 km/s. I will also present the results from an observational study on strong MgII absorbers in quasar spectra, where we have found that many of these absorbers may arise in radiation driven outflows from the quasar itself. || Physics LH-II || Mahavir Sharma, RRI ||
 * 29/10/2013 || **Some X-ray studies of neutron stars**

Neutron stars appear in many varieties with a range of observational features starting from radio to the gamma-rays. Certain aspects of the neutron stars are best studied using the X-rays emitted from these objects, either on their own, or due to accretion of matter from a companion star. I will mention some studies of accreting neutron stars that we have pursued: i) accretion torque, ii) orbital evolution of binary X-ray stars and orbital glitches, iii) quasi-periodic oscillations and their implications, iv) self absorption in X-ray pulsars v) cyclotron absorption lines in X-ray pulsars - study of neutron star magnetic field and v) thermonuclear X-ray bursts and their reprocessing. Some of the important aspects of neutron stars that will be probed much better with ASTROSAT and an X-ray polarimeter and potential use of X-ray pulsars for deep space navigation will also be discussed. || Physics LH-II || Biswajit Paul, RRI ||
 * 05/11/2013 || **Viscosity in collisionless plasmas: from angular momentum transport in black hole accretion disks to aerodynamic drag on solar coronal mass ejections**

Collisionless plasmas are ones where the constituent particles rarely (if at all) collide with each other. Our usual notions of macroscopic transport properties such as viscosity and conductivity, which appeal explicitly to frequent inter-particle collisions, cannot be applied to such plasmas.

We consider the problem of viscosity in two situations involving collisionless plasmas - a) hot accretion disks around black holes and b) the solar wind. One appeals to fluid viscosity in order to explain angular momentum transport in accretion disks around black holes. Viscosity is also invoked in attempting to explain the origin of the "aerodynamic" drag experienced by coronal mass ejections from the solar corona as they travel through the solar wind.

We will outline a first principles formulation of viscosity in collisionless plasmas and show how it successfully explains the essential observational signatures in these two contexts. || Physics LH-II || Prasad Subramanian, IISER Pune ||
 * 17/12/2013 || **<span style="background-color: #ffffff; color: #222222; font-family: &#39;Book Antiqua&#39;,Palatino,serif; font-size: 13px; text-align: start;">Type II Supernovae: illuminating a dusty Universe **

<span style="background-color: #ffffff; color: #222222; font-family: &#39;Book Antiqua&#39;,Palatino,serif; font-size: 13px; text-align: start;">Core-collapse supernova have a considerable impact on the diversity of celestial phenomena, in that the collapsing core of the massive progenitor forms a compact object with exotic states of matter, while the metal-enriched ejecta mixes with the ISM, initiating the next generation of star formation. As the ejecta cools, some of it is expected to condense in to dust, and, indeed, theoretically, type-II SNe, with their massive progenitors, are expected to the main source of dust, especially in the early universe. But are they? In this talk, I will present an investigation of the "supernova dust problem", using both recent theoretical advances in the evolution of massive stars, as well as observations of bright, type-II supernovae in the Chandra-Galex-optical-Spitzer-GMRT era. || Physics LH-II || Firoza Sutaria, IIA ||