ASI XXVII
2 0 0 9

I will propose a unified model to explain QPOs observed from black hole and neutron star systems globally. Considering accretion disks to be damped harmonic oscillators, I will explain various properties of QPOs, particularly the kHz ones, for both the types of the compact object. The model explains successfully QPOs for ten different compact sources: six neutron stars and four black holes. On the other hand, since the discovery of the solution of the Einstein equation for a rotating black hole by Roy Kerr in 1963, the spin parameter (which is essentially specific angular momentum) of the black hole has not been established yet from observed data which could theoretically be allowed in the range of 0-1. In explaining QPOs, I will determine the spin parameter of black holes GRO~J1655-40, XTE~J1550-564, H1743-322, GRS~1915+105.

Study of solar oscillations has provided us detailed information about the rotation rate in the solar interior. With the availability of helioseismic data over an entire solar cycle it is now possible to study the temporal variations in the rotation rate and its gradients. These results provide a test of solar dynamo theories.

The solar gravity modes are the best probes to improve our knowledge on the solar interior, as they spend most of their time in the radiative zone, which represents 98% of the solar mass. Many attempts have been led to observe them using different techniques: either individually, then adding some statistical approach (Gabriel et al. 2000, Turck-Chieze et al. 2004) or more recently, globally leading to the detection of the signature of asymptotical properties of these modes (Garcia et al. 2007). Then, several theoretical works have been done to quantify the effect of detecting g modes on solar modeling and on the rotation profile (Garcia et al. 2008, Mathur et al. 2008). We will give here an update on the g-mode detection as well as an example of a theoretical work showing how their detection would improve our knowledge on the dynamics of the solar core.

Local helioseismology presents valuable tools to study the sub-surface structure and dynamics of magnetic fields in the upper convection zone, most notably those associated with sunspots. The different methods, namely, time-distance helioseismology, helioseismic holography and ring diagram analysis, have progressed substantially in the past two decades, but are still without due considerations of crucial magnetohydrodynamic interactions between magnetic fields and acoustic waves. We breifly review the recent progress followed by a discussion of various issues and problems. We also discuss new developments in 3-dimensional tomographic imaging of flows and structures beneath sunspots from time-distance helioseismology, with a focus on problems associated with near-surface magnetohydrodynamic interactions between the acoustic waves (p modes) and magnetic fields.

The Global Oscillation Network Group (GONG) is a community-based program to conduct a detailed study of solar internal structure and dynamics using helioseismology. In order to exploit this new technique, GONG has developed a six-station network of extremely sensitive, and stable velocity imagers located around the Earth to obtain nearly continuous observations of the Sun's five-minute oscillations, or pulsations. In India, the Udaipur Solar Observatory is hosting one of the six telescopes of the GONG network. This network of telescopes became operational in October, 1995 and has now completed observing the Sun for the full solar cycle, i.e. cycle 23. In this talk, I shall summarize the significant contributions of the GONG observations to the field of helioseismology.

The magnetic field of the Sun originates deep in it's interior and subsequently erupts out of the surface as sunspots and defines the magnetic, radiative and energetic environment of the heliosphere. There, it has profound effects on planetary atmospheres, on our technologies based in space and here on Earth. In this lecture, I will review advances in solar magnetohydrodynamic dynamo theory -- the subject which deals with the origin and variability of solar magnetic fields and present our current state of understanding. I will also briefly discuss attempts to develop global models of solar coronal and heliospheric magnetic fields -- that seek to characterize the magnetic environment of the Sun-Earth-System.

Observations of very high spatial resolution magnetic fields and associated flows are very important in understanding the physical mechanisms behind the small-scale structuring of the solar atmosphere. These observations will impose important constraints on the Magneto Hydrodynamic simulations, especially the simulations of the solar photosphere. They can also play as a tracer or indicator of sub-surface structures and will probably play a major role in constraining the inversion results from the local helioseismology. However, observations of the small-scale magnetic field poses major challenges especially when observed from the ground-based solar telescopes. They evolve much faster than the large-scale structures and also more severely affected by the turbulent Earth atmosphere. Over the last eight years, there are overwhelming observations on the small-scale structures due to the successful implementation of the Adaptive Optics in solar observations. The recent successful launch of Hinode along with a visible light vector polarimetry has provided wealth of informations on the small-scale structures at the solar photosphere. This paper will discuss the recent findings from these observations and also list its limitations. The future challenges to overcome the limitations will also be highlighted.

There have been several instances in recent times when solar wind densities at 1 AU have dropped to values up to two orders of magnitude below the average. In addition, these low values have persisted for extended periods of up to 24 hours or more. Such low-density solar wind anomalies are also accompanied by lower than normal solar wind flows at 1 AU. These rather rare phenomena are now referred to as ''solar wind disappearance events''. One consequence is a dramatic expansion of the Earth's magnetosphere and bow shock. In the case of the well-known disappearance event of 11 May 1999, the expanding bow shock, normally located at ~10 Earth radii, reached an upstream distance of nearly 60 Earth radii, the lunar orbit. Using both ground-based interplanetary scintillation (IPS) observations and space-based observations (SoHO, ACE, and WIND spacecraft), I discuss in this talk, the progress made in our understanding of these unique events on the Sun, in the interplanetary medium, and at Earth. With the exception of co-rotating interacting regions (CIR), disappearance events provide, to the best of our knowledge, the first link between the Sun and space weather effects at 1 AU, arising from non-explosive solar events.

This talk starts with the history of the law of gravitation which essentially emerged from the database of plantary motion and Kepler's analysis thereof. Today we marvel at information technology,especially the rapid communication across continents. This became possible because space technology could launch satellites based on the law of gravitation. Thus we ultimately owe these developments to the painstaking astronomical observataions of planets taken over hundreds of years.\ Other examples will be given to counter the comment that astronomy is a subject without any practical use. It will also be shown how some observations underway today may contain useful information for the survival of our civilization on Earth.

Neutral fluorine lines were identified in the optical spectra of hydrogen deficient stars: Extreme helium, and R Coronae Borealis stars. These stars are considered to be in their advanced stages of stellar evolution. The fluorine lines identified provide the first measurement of fluorine abundance in these stars. The results show that fluorine is overabundant in these stars. The overabundance of fluorine provides us with evidence for the synthesis of fluorine in these stars that I will discuss in light of single star evolution and the expectation from the binary star evolution.

Stars and planetary systems are formed when portions of giant molecular clouds collapse and heat up. Observation of the chemical changes in the molecular composition of the gas and dust particles improves our understanding of the time scales and histories of the different chemical processes which influence the different stages of star formation. We shall review the current understanding of the grain-surface and gas-phase interstellar chemistry in the giant molecular clouds. Starting with the formation of molecular H$_2$ on the grain surfaces, we shall discuss major chemical processes in dark cores, role of deuterium fractionation in dark cores, effects of depletion of molecules onto grain surfaces, corinos and hot cores,formation of large carbon chains and highlights of the radiation induced chemistry in PDRs.

We are pursuing multi-wavelength studies of a few star-forming regions to study the star formation scenario and effects of massive stars on low-mass star formation. The young stellar objects (YSOs) in these regions have been identified using the near-infrared colours and slitless spectroscopy. The colour-magnitude diagram of the YSOs indicates that the majority of these objects have ages between 1 Myr to 5 Myr, indicating a non-coeval star formation in young clusters. There is evidence for triggered star formation in the periphery of cluster regions. We shall discuss a few aspects of triggered star formation in/ around young star clusters.

Study of 16 open clusters has been taken up with the primary aim being the study of initial mass function (IMF) and its dependence on the cluster age as well as the galactocentric distance. The deep CCD photometric observations of all the clusters under study were done in UBVRI passbands using the 2m HCT at the IAO and the 1.02m telescope at the VBO in India. The reduction and data analysis were carried out with the help of packages in IRAF. The distances of the programme clusters have been found to be in the range of 0.916 kpc to 6.9 kpc, while the log(age) of these clusters are found to be spanning over 6.6 to 9. The IMF slopes of the 2 embedded and 6 young open clusters are in good agreement with the Salpeter value, while the MF slopes of the 4 intermediate age open clusters were found to be having steeper slopes compared to that of the Salpeter value. By combining our results with those available in the literature, we have found a weak evidence for the dependence of the MF slopes on the cluster age, while there is no effect of the galactocentric distance on these slopes.

Solar activity affects our space environment, thereby influencing various aspects of human life. The solar magnetic cycle can affect humankind by disrupting radio communication, damage electronic equipment in artificial satellites, trip power grids, and make polar airline routes dangerous. So it is vitally important to develop capabilities for predicting strengths of the 11-year cycles of solar activity. The solar magnetic cycle is believed to be produced by a complex dynamo mechanism involving a combination of deterministic and random processes. Dynamo theorists have now arrived at a consensus regarding processes in a solar dynamo model. In this thesis I will describe a two dimensional kinematic model for the solar magnetic cycle. This model produces a solar like butterfly diagram and also gives the correct phase relation between poloidal field and the toroidal field. I will also describe how the model was used to predict future solar cycles as well as hemispheric dependence of active region helicity. To study evolution of helicity in greater detail a 1-D model of twisted fluxtube rising in a convection zone was also studied. We concluded that subsurface mechanisms play an important role in the distribution of helicity in the active regions.

Solar magnetic fields play an important role in a variety of activity phenomena observed on the Sun. They are present right from Sun’s deep radiative interior up-to the heliopause. Their evolution, mainly due to photospheric dynamics and flux emergence, leads to activity phenomena like flares, filament eruptions, Coronal Mass Ejections (CMEs). Thus, task of measuring solar magnetic fields is of utmost importance in solar physics. However, the measurement of solar magnetic fields is very challenging task. The challenge comes mainly from the fact that the measurements need to be done remotely by sensing the polarization (due to Zeeman effect) of solar spectral lines. Also, the distortions in imaging due to atmospheric "seeing" leads to poor spatial resolution and effects polarization measurements. The focus of this thesis is on the measurement aspects of solar magnetic fields. A new instrument developed for measuring the vector magnetic fields in the photosphere is described. The instrument is called Solar Vector Magnetograph (SVM). The key features of the instrument like symmetric imaging optics, a tunable Fabry-Perot, a dual-beam polarization analyzer, an indigenous instrument control software and a data-reduction and analysis package GUI are described. Finally, the techniques for inferring magnetic field vector from the observed spectro-polarimetric data are described. I conclude with application of vector-fields to sunspot-seismology.

A dual beam polarimeter has been installed as a backend instrument to the spectrograph at the Kodaiakanal Tower Telescope (KTT). An efficient modulation scheme was worked out for the measurement of general polarisation state of the light. It was confirmed through an experiment that the precision in the polarisation measurement is limited by the photon noise. A good comparison was found between the photospheric magnetic field measurements at KTT and Hinode/SOT, after spatial smearing of later measurements by 5.12''x5.12''. Spectropolarimetric observations of several active regions have been carried out towards the goal of understanding the magnetic coupling between the photosphere and chromosphere. For this purpose the spectral lines H alpha (656.28 nm), which forms in the chromosphere, and Fe I line (6569.22 nm), which forms at the photosphere, are used. The results from these observations will be presented in conjunction with the EUV and X-ray structures observed by SOHO/EIT and Hinode/XRT, respectively.

we present high speed photometric observations, to serach for rapid oscillations in chemically peculiar (CP) stars of spectral type A -F. All the observations were taken from 104 cm Sampurnanand telescope aT ARIES equipped with three channel fast photometer. The aim of the present thesis is to search variability in CP stars. Rapidly oscillating Ap starsare the most easily observable main-sequence pulsating stars, other than sun. They possess high magnetic field in the driving and controlling of the pulsations can studied by observing roap stars. The main results of the present study, that we have detected shot peiod oscillations in HD 103498 and HD 151878. We also found the delta scuti pulsation in Hd 25515 and confirms the signature of photometric variability of stars HD 113878, HD 118660, HD 13079 and HD 13038. During survey programme we have also done photometric observations of six eclipsing binary system of Algol type for the study of pulsations in their primary component. We found delta scuti pulsation in X Tri, RW Per and TV Cas.

The Crab and Geminga pulsars were observed with the Pachmarhi Array of Cherenkov Telescopes (PACT). The pulsar data collected during the 7 year period spanning 2000 - 20006 have been used for searching pulsed TeV gamma rays from these objects. A long stretch of data collected, new computer codes, "TEMPO" package, contemporaneous pulsar elements, known period as measured at lower wavelengths etc. have been used for this search. No significant evidence for pulsed emission of gamma rays at a threshold energy of about 825 GeV were found in both cases. Upper limits for time averaged gamma ray flux from these objects have been set and compared with other ground based observations.

Galaxy interactions and mergers are common and lead to a significant morphological and dynamical evolution of galaxies. The following main results from our work will be highlighted here. The new regime of unequal-mass mergers of galaxies with a mass ratio in the range of 4:1-10:1 has been studied via N-body simulations (Bournaud, Jog & Combes 2005). These are more likely to occur than the standard equal-mass mergers studied in the literature. The unequal-mass mergers are shown to result in peculiar, hybrid systems which have spiral-like exponential profiles for the luminosity but have elliptical-like kinematics where the main support is from pressure. These features naturally explain the results obtained from the data analysis of a sample of Arp mergers (Chitre & Jog 2002). N-body simulations of successive mergers of unequal-mass galaxies are shown to lead to the formation of elliptical galaxies (Bournaud, Jog & Combes 2007). Such sequential mergers are unavoidable in the hierarchical formation of galaxies. Several interesting, open dynamical issues regarding these merger remnants will be discussed.

The dynamical evolution of field galaxies differs from that in denser environments such as clusters since the galaxies are subject to several physical processes such as tidal interaction and ram pressure. In clusters, the velocity dispersion and matter densities in the intracluster medium are large, leading to hydrodynamic processes such as ram pressure stripping dominating the galaxy evolution. The density-morphology relation and Butcher-Oemler effects observed in clusters are evidences of these processes. Since more than 65% of galaxies occur in groups, a significant fraction of their evolution should occur in groups before they enter cluster-like environments. However in smaller tenuous group environments, the velocity dispersion and densities in the intragroup medium are lower, suggesting that only tidal interactions might be important in influencing the evolution of the member galaxies. However a paradigm shift is now taking place; several observations of groups and cluster outskirts (together with numerical simulations) suggest that (1) hydrodynamic processes such as ram pressure stripping are indeed active in low density environs and (2) significant evolution of galaxies occurs in group environs and in cluster outskirts before they enter dense cluster environs. In this talk, we discuss our results from low radio frequency observations using the Giant Metrewave Radio Telescope which lend support to this scenario.

Absorption lines in quasar spectra can be used to probe the interstellar matter in galaxies at various cosmic epochs, selected only by gas cross-section, not galaxy brightness or morphology. Thus quasar absorption lines can provide a powerful, flux-independent tool to study galaxy evolution, complementary to the flux-limited galaxy imaging studies. Since the cosmic histories of stars, gas, and metals are closely coupled, quasar absorption systems offer important constraints on the cosmic star formation history. We will review the implications for the star formation history from the evolution of metals and gas in quasar absorption systems. Furthermore, we will discuss direct constraints on the star formation history of the absorbers from imaging searches for the underlying galaxies and other methods.

Understanding the physical processes that govern the conversion of gas into stars is crucial to understanding galaxy formation and evolution. Since these processes, viz. the cooling of baryons and the subsequent star formation and feedback are complex and poorly understood, empirical relations between the gas column density and the star formation rates surface density play an important role in semi-analytical models and simulations. In this talk I will present results from a study of the relationship between the gas column density and the star formation rate surface density for a sample of 23 extremely faint dwarf irregular galaxies. Our sample galaxies have a median HI mass of $2.8 \times 10^7$ M$_\odot$ and a median blue magnitude M$_B \sim -13.2$. In hierarchical galaxy formation models small galaxies form first, and star formation recipes for dwarf galaxies are hence particularly relevant. For our galaxies we derive the star formation rate surface densities from GALEX data, while the gas column density is derived from the GMRT based FIGGS HI 21cm survey data.I will present and discuss the observed correlations between star formation and gas column density both on on global scales as well as small (400 and 200 pc) scales.

An understanding of the star forming processes in galaxies is an important prerequisite to understanding their formation and evolution. The study of actively star forming galaxies in the distant universe has been a thrust area for major studies using different ground and space based facilites. This requires a detailed understanding of the process in the nearby universe. The ultraviolet wavelengths are naturally suited for studying young, hot stars and nebulae associated with the star formation process. However, as with most astrophysical processes, data from multiple wavebands must be collated for a definitive understanding. We review the salient properties of star forming galaxies as seen from UV data from recent missions and intercompare the information derived from the UV and other bands. In particular, recent large surveys in different wavebands give new insights into and evoke new queries about classes of galaxies in terms of the amount and type of star formation. The role and suitability of the proposed Indian UV missions for such studies will also be discussed.

Jets from AGNs often plough through the ISM of the host galaxy and emerge into the tenuous gas beyond. The density structure in the intergalactic medium governs the advance and shapes the flow of the re-accelerated synchrotron plasma beyond the termination shock, and the anisotropy in the coronal gaseous environment of the host galaxy redirects the backflow. Additionally, the relatively light synchrotron bubbles embedded in the intergalactic medium experience buoyant displacement towards directions governed by the gravitational acceleration vector of the large scale structure. I give examples of such interactions revealed by radio-optical studies of radio galaxies and their environments.

In the current paradigm of cold dark matter cosmology, large-scale structures assemble through hierarchical clustering of matter. Major heating of infalling matter takes place through cosmic shock waves, arising in gravity-driven supersonic flows of intergalactic matter onto dark-matter dominated collapsing structures such as pancakes, filaments and clusters of galaxies. Non-thermal radiation from relativistic particles accelerated in structure shocks will be observable in radio, X-ray and Gamma-ray wavelengths, but only radio emission has been detected so far. Non-thermal radiation probes several important components of the cosmic environment: intergalactic gas, magnetic fields and cosmic-rays. The speaker will highlight these aspects and discuss some observations which will soon become possible with the new generation radio, X-ray and Gamma-ray facilities.

Vigyan Prasar (VP), Department of Science and Technology, has planned an ambitious programme for popularization of astronomy in India during the International Year of Astronomy (IYA) 2009 in general; and TSE-2009 in particular, which would take place on 22 July 2009. The programme would encompass aspects from history of astronomy to the present state of knowledge and technology with emphasis to India. It is proposed to utilize different means, media and modes for the purpose. In particular, the programmes envisaged include publication of titles on astronomy at popular level, a 54-episode radio serial in 19 indian languages, and a 26-episode television serial on astronomy, interactive CDs and activity packages for school students and teachers; and awareness / training programmes for resource persons / science communicators, and school / college students at various levels. A novel feature will be the utilization of VP's countrywide Satellite Interactive Terminal network using Edusat for astronomy popularization.

Physical Research Laboratory will install a 50 cm aperture Multi Application Solar Telescope (MAST) in late 2009 at the island site of the Udaipur Solar Observatory. Among the various steps leading to the project, the Fried’s parameter was determined using short exposure H-alpha images obtained over a period of 2 years. This value was used to determine the size of the telescope that optimally benefits from adaptive optics. A prototype AO system was also developed. Preliminary optical design of the telescope and experimentation on insolated mirrors was used to fix the specifications. This was then given to a vendor for fabrication. The back-end instruments are being developed in-house. A new building with a collapsible dome is being built on the island. MAST will address evolution of photospheric magnetic stresses along with accompanying dynamics of the associated chromospheric magnetic structures. Availability of long observational periods at Udaipur will be exploited to provide a lasting contribution to the topic of solar magnetic fields.

The Indian Institute has proposed a 2-m class solar telescope that will be able to resolve the fundamental scales that determine the structuring of the solar atmosphere. Precise quantitative measurements of vector magnetic fields will be undertaken in order to understand physical processes on the Sun. The main science goals include: (a) study of magnetic fields at the network boundaries and in the internetwork, (b) fine structure of sunspots including the Evershed flow, (c) the dynamics of active regions, (d) thermodynamics of the chromosphere, and (e) identification of mechanisms responsible for chromospheric and coronal heating.

A 3.6m optical telescope is being set up at Devasthal site (79E 29N) situated in the Himalayan region with a ground level median seeing of about one arcsec. The design of the telescope is optimized for carrying out high resolution optical spectroscopy and the seeing limited optical-near infrared imaging in a field of around 10 minutes of arc. The telescope has a RC design with a clear aperture of 3.6m, an effective focal ratio of f/9. The primary mirror is made up of zerodur glass and it shall have active supports. For mounting instruments, the telescope has one axial and two side ports at the Cassegrain focus. In order to take advantage of ten percentile seeing (0.7 arcsec - FWHM) at Devasthal, the eighty percent encircled energy of a point source is set to lie below 0.4 arcsec over 10 minutes of arc field at Ritchey-Chreitien Focus near zenith. The telescope is proposed to be commissioned by 2012. In this talk, we summarise present status and future plan for the 3.6m Devasthal optical telescope observatory including the overall telescope design, back-end instrumentation, enclosure and aluminizing facility.

In this presentation I will outline the instruments which are in development at RRI. Some of them are stand-alone while others are special-purpose receivers that may add value to the existing facilities. These instruments cover a wide range in frequency starting from meter to mm waves in radio and X-rays. The presentation will outline (1) RRI's participation in the Murchison Widefield Array (MWA) project.The main objective of MWA is to develop powerful new capabilities for radio astronomy and heliospheric science in the frequency range 80 to 300 MHz, optimized for extremely wide fields of view and unprecedented sensitivity at those frequencies. (2) Development of a 50 MHz system for GMRT to carry out a low frequency survey of the sky visible to GMRT with arcmin resolution and unprecedented surface brightness sensitivity. (3) Development of an X-ray polarimeter that will give us a unique opportunity to expand the field of X-ray astronomy into a hitherto unexplored dimension with a view of the high energy universe through a completely new window. (4) An all sky telescope for detecting EoR (5) Possible new -initiatives in the near future to build innovative instruments for low frequency and mm wave radio astronomy.

While Gamma ray astronomy has come of age with detection of many celestial sources, there is a large decease in the number of sources with increasing energy . This indicates possibility of dramatic changes in the characteristics of celestial sources at gamma ray energies of 10 -100 GeV.While the new satellite experiment GLAST is expected to explore this energy range with direct detection, two atmospheric Cerenkov experiments are being undertaken to reduce the energy threshold in this technique by exploiting the several advantages at high altitudes. The HAGAR ( HIGH ALTITUDE GAMMA RAY ) experiment , which is expected to have energy thresholds of 60-70 GeV, was commissioned recently and has started taking data on several sources since September 2008. The initial emphasis will be on pulsar observations. Further efforts to reduce the energy threshold to 20-30 GeV is also being undertaken with the MACE( MAJOR ATMOSPHERIC CERENKOV EXPERIMENT) detector which will have a huge (21 meter diameter) telescope at Hanle. These two experiments will be a part of HIGRO, the Himalayan Gamma Ray Observatory which will represent the overall efforts of the country (including TIFR, BARC and IIA) in the field of gamma ray astronomy.

I will consider in my talk various large data bases which have become available to astronomers, or expected to become available over the next few years. I will describe some ways in which the vast data can be accessed, managed, analysed and visualized. I will consider briefly some new scientific projects which can be launched using the data and the tools.

To further our understanding of our universe, the international astronomical community has proposed three very large aperture ground based optical-IR telescopes. These are: the 24m Giant Magellan Telescope (GMT) led by the Observatories of the Carnegie Institution (USA), the Thirty Meter Telescope (TMT) led by University of California and California Institute of Technology (USA), and the European Extremely Large Telescope (E-ELT) led by European Southern Observatories. The three project groups have shown keen interest in India's participation in building and using these facilities. In response to these invitations, the Indian community has initiated an intense debate on such participation, including a national meeting held in Sept. 2008, and a meeting with funding agencies, DST and DAE, in Oct. 2008. The funding agencies have requested the community to prepare a detailed report and submit it by the end of April, 2009. In this meeting, we will give an update on the status of this effort.

To further our understanding of our universe, the international astronomical community has proposed three very large aperture ground based optical-IR telescopes. These are: the 24m Giant Magellan Telescope (GMT) led by the Observatories of the Carnegie Institution (USA), the Thirty Meter Telescope (TMT) led by University of California and California Institute of Technology (USA), and the European Extremely Large Telescope (E-ELT) led by European Southern Observatories. The three project groups have shown keen interest in India's participation in building and using these facilities. In response to these invitations, the Indian community has initiated an intense debate on such participation, including a national meeting held in Sept. 2008, and a meeting with funding agencies, DST and DAE, in Oct. 2008. The funding agencies have requested the community to prepare a detailed report and submit it by the end of April, 2009. In this meeting, we will give an update on the status of this effort.