Astronomy & Astrophysics Seminars

Comets are small kilometre-sized bodies that remain largely inactive for most of their orbital evolution and become active as they approach the Sun. They originate from two distant reservoirs: the Kuiper Belt (~50-100 au) and the Oort Cloud (~1000-100000 au). Long-period Comets (LPCs), with orbital periods greater than 200 years, are believed to emerge from the Oort Cloud. A subset of LPCs, known as dynamically new comets (DNCs), is thought to be entering the inner Solar System for the first time. These objects are of particular interest for future in-situ comet missions, as their primitive material has never been exposed before, and studying their composition provides important constraints on the conditions of the early Solar System. While spectroscopic observations provide insights into their chemical composition, identifying and confirming a comet as a DNC requires detailed dynamical modelling of its orbital history.

In this talk, I will present observational studies of cometary spectra together with dynamical simulations aimed at understanding their origin and evolution. I will explain the N-Body simulation code and the role of forces that act in addition to gravity. Finally, I will discuss a potential new classification: dynamically resilient comets, which cannot be identified solely from orbital elements.

The study of compact object populations has evolved from the first observational identification of white dwarfs, pulsars, and black hole candidates to the current era of large astronomical surveys. Today, more than 150 Galactic neutron  stars and black holes with measured masses are known, complemented by over 180 compact object mergers detected through gravitational waves. With an increasingly detailed understanding of the diverse environments that host these objects and the physical processes governing their formation and evolution, we are now in a position to investigate the statistical properties of compact object populations and address long-standing open questions. In this talk, I will discuss how the current and upcoming generation of wide-area surveys is transforming our ability to uncover and characterise compact objects across the electromagnetic spectrum. In particular, I will highlight the role of the eROSITA all-sky X-ray survey in revealing accreting neutron stars and white dwarfs, and how systematic optical spectroscopic follow-ups play a crucial role in this regard. By combining large, homogeneous survey datasets with targeted follow-up, we are entering a regime where population-level studies can be carried out with unprecedented statistical power. I will outline how these approaches allow us to build a unified view of compact object populations in the Milky Way and nearby galaxies.

Active Galactic Nuclei (AGN) are highly variable sources powered by accretion onto a Supermassive Black Hole (SMBH), exhibiting flux variations across all wavelengths on timescales ranging from hours to years. X-ray variability, in particular, provides a direct probe of the innermost regions of the accretion flow and the geometry of the hot corona. These variations are often stochastic in nature, however, in some rare cases, coherent signals known as Quasi-Periodic Oscillations (QPOs) have been detected.

A QPO is a nearly regular, but not strictly periodic, variation in the observed flux of an astrophysical source. Significant QPO detections in AGNs are rare compared to that in their galactic binary counterparts, since variability timescales are expected to scale inversely with black hole mass. QPOs in AGN are thought to arise from characteristic timescales in the accretion disk, such as orbital motion, disk instabilities, or relativistic precession near the SMBH. From an advective flow point of view, QPOs can also be generated by oscillations of the Comptonizing region, which occur when the resonance condition is satisfied, i.e. when the heating and cooling timescales of the hot corona roughly match.

In this talk, I will provide an overview of X-ray variability and QPO detection in AGN. Additionally, I will present the results from the timing analysis of the Seyfert galaxy Mrk 530, including the detection of a possible QPO candidate observed simultaneously in both the X-ray and UV wavelength regimes.

Fabry–Pérot (FP) wavelength calibrators are increasingly replacing traditional Uranium–Argon (UAr) hollow cathode lamps in high-resolution spectroscopy. By producing a dense and uniform comb of spectral lines through multiple-beam interference, FP calibrators enable improved local wavelength solutions and enhanced precision. They are also widely used for tracking instrumental drifts on nightly timescales.

In this talk, we present the Fabry–Pérot wavelength calibrator developed for the PARAS-2 spectrograph. We highlight its off-sky radial velocity performance and outline the algorithms used for its characterization.

Magnetic fields play a significant role in regulating massive star formation, and their interplay with gravity, turbulence, and stellar feedback ultimately shapes the evolution of star-forming regions. However, the relative contributions of these physical processes are scale-dependent and can vary from clump to core scales. Understanding this multi-scale energy balance remains a key challenge. 

In this talk, I will discuss the multi-scale nature of magnetic field structures and their interplay with other physical forces in the well-studied G35.20−0.74 star-forming complex. I will present a multi-wavelength polarimetric analysis of two prominent sub-regions in this star-forming complex using far-infrared and millimeter polarization observations to probe the magnetic field morphology  and its dynamical significance. By combining magnetic field strength estimates with an energy balance analysis, the dominant physical mechanisms operating in these two sub-regions are investigated. These results provide important insights into how magnetic fields regulate collapse in some regions, while in others they respond dynamically to stellar feedback.

Active Galactic Nuclei (AGN) are powered by accretion onto supermassive black holes and, in the case of blazars, exhibit emission dominated by relativistic jets closely aligned with our line of sight. In the classical orientation-based unification scheme, type-1 AGN, type-2 AGN, and blazars are regarded as fundamentally similar systems viewed at different angles. However, the growing discovery of AGN undergoing intrinsic state transitions on human timescales challenges this static framework and points to dynamical evolution within the central engine. 

In this seminar, I will present results addressing both the long-term persistence and rapid transitions of the blazar state in beamed radio quasars. Using high-quality optical light-curves from the Zwicky Transient Facility (ZTF) survey and the polarization measurements from the RoboPol survey, we investigated the persistence of the blazar state in individual radio quasars. We find that ~90% of beamed radio quasars retain their blazar mode over 3–4 decades, although transitions on year-like timescales can also occur, likely associated with short-lived jet events. Complementary systematic intranight optical variability (INOV) studies of 14 high-redshift blazars (FSRQs) provide the first characterization of rest-frame UV intranight variability, suggesting that UV synchrotron emission may arise from a particle population distinct from that producing up to near-infrared/optical emission. Extending this analysis to low-mass AGN (MBH ~10⁶ M⊙), we detect blazar-like activity, implying that relativistic jets can operate even in substantially lower-mass systems.

Finally, I will discuss rare transition objects, including the radio-state transition quasar J0950+5128 and the changing-look blazar OQ 334, which serve as natural laboratories for probing the onset and evolution of jet activity and its connection to accretion processes. Together, these results establish optical variability as a powerful probe of AGN state evolution and jet–accretion coupling.

In this talk, I will explore two complementary views on the evolution of the Milky Way Galaxy. In the first part, I will present a chemo-dynamical analysis of stars from the APOGEE survey within 5 kpc of the Sun. We separate these stars into thin disk, thick disk, innerhalo, and outer halo populations based on their orbital properties. We find systematic metallicity gradients within these populations. The inner halo has more α-elements, and we also see substantial trends with orbital radius and eccentricity. These results show how chemical enrichment, dynamical heating, radial migration, and accretion all work together to shape the Galaxy as it is today. In the second part, I will turn to the nucleosynthetic origin of trans-iron elements in carbon-enhanced metal-poor stars enriched with both s- and r-process elements (CEMP-rs). Despite decades of progress, the astrophysical sources of these elements remain uncertain. These elements are thought to be produced by a variety of nucleosynthetic processes, the main ones being the so-called slow (s) and rapid (r) neutron capture processes. An intermediate neutron capture process (i-process) is also thought to occur at neutron densities intermediate between the s- and r-processes. We report the discovery of tantalum, a rare third r-process peak element and a powerful diagnostic of i-process nucleosynthesis, in CEMP-rs stars. The pattern of its abundance provides strong evidence for i-process enrichment, giving us new clues about where trans-iron elements come from. Together, these studies connect the Milky Way’s structure and motion with unusual ways of making heavy elements, helping us better understand how our Galaxy formed and acquired its chemical makeup.

Black holes of masses over a million times our Sun, inhabit the centres of most galaxies and appear to co-evolve with their host galaxies. While we do not yet fully understand how galaxies and their central supermassive black holes grow hand in hand, evidence suggests that such black holes play a significant role in regulating galaxy assembly. We are able to spot these black holes to the far reaches of the universe if and when they accrete matter, which is also what causes them to impact their environments out to spatial scales that are well beyond their gravitational sphere of influence. In this talk I will discuss the understanding that has emerged from studies of the systematics of such accreting supermassive black holes from across the electromagnetic spectrum, and also pointers to the way forward.

Recent surveys and simulations show that stellar feedback operating through radiation, winds, H II region expansion, outflows, and supernovae regulates where, when, and how efficiently molecular gas forms stars in the Galaxy. In this talk, I outline the current physical picture of feedback-driven cloud evolution, emphasizing shell and filament compression, photoevaporation and dispersal, turbulence injection, and the feedback-gravity competition that can both trigger secondary star formation and suppress further collapse. I use observational diagnostics that connect feedback to dense-gas formation, including dense-gas tracers, kinematics, and dust and infrared constraints, to highlight recent results. These include FIRESTORM I, the first paper of the FIRESTORM project, which targets a feedback-shaped environment to quantify how feedback restructures dense gas and redistributes star formation activity. Evidence from simulations and cloud-lifecycle measurements suggests that the net impact of feedback depends on geometry and evolutionary timescale, motivating multi-tracer mapping and kinematically resolved tests that link cloud structure to star formation.

Neutron stars in low-mass X-ray binaries provide unique laboratories for studying matter under extreme gravity, density, and magnetic fields. These systems consist of a neutron star accreting matter from a low-mass companion star, typically through Roche-lobe overflow. In such systems, the neutron star usually possesses a relatively weak magnetic field (~10⁷-10⁹ G), allowing the accreted material to spread over the stellar surface rather than being funneled directly onto the magnetic poles. As a result, the accumulated fuel can undergo unstable nuclear burning, leading to sudden thermonuclear explosions on the neutron star surface, observed as thermonuclear X-ray bursts. In some energetic bursts, the radiation is strong enough to temporarily lift the photosphere, causing a photospheric radius expansion (PRE). Some bursts also show burst oscillations, rapid periodic variations caused by localized hotspots in the burning layer. In this talk, I will present studies of thermonuclear X-ray bursts, including photospheric radius expansion events and evidence of burst-disk interaction. I will also discuss the results from a newly discovered accreting millisecond X-ray pulsar with numerous bursts, where spectral and timing analyses reveal disk reflection and the first detection of burst oscillations. Overall, these studies demonstrate how thermonuclear bursts can be used as powerful tools to probe neutron star properties and accretion physics in extreme environments.

MPE together with its PANTER X-ray test facility is involved in the development, testing and calibration of X-ray optics, Detectors, complete telescopes for most existing  X-ray observatories and future large missions. I will present the X-ray test facility. I will also describe the missions and technologies they use as well as the types of measurements that are performed to ensure the flight readiness of the missions as well as providing as sturdy on ground calibration  to support the in-flight calibrations. These activities now also are coordinated the IACHEC  cross mission calibration group.

Active galactic nuclei are the most luminous and energetic sources in the universe, powered by the accretion of matter onto the supermassive black holes (SMBHs) located at the centers of the host galaxies.  In the optical/UV range, the AGNs are commonly classified as type 1 or type 2 based on the widths of their optical emission lines. Type 1 AGNs show both broad emission lines (BELs) and narrow emission lines (NELs), whereas type 2 AGNs show only NELs in their UV/optical spectra. In recent years, several tens of subclasses of AGNs have been discovered, exhibiting dramatic optical and X-ray spectral variability on timescales ranging from months to decades. These are known as changing-look AGNs and are currently an open issue in AGN physics.

In this seminar, I will present a 17-year (2008–2025) multiwavelength study of the changing-look AGN NGC 3822, combining X-ray and UV data, along with optical observation from the Very Large Telescope and the Himalayan Chandra Telescope. Long-term optical monitoring reveals clear evolution in the emission-line properties, including the appearance and disappearance of broad Balmer lines, confirming the changing-look nature of the source. I will discuss the observed spectral-state transitions, their connection to X-ray/UV variability, and what these results imply about the possible drivers of changing-look behaviour, such as variable obscuration and changes in the accretion rate.

Cataclysmic Variables (CVs) are close interacting binary systems consisting of a white dwarf accreting material from a late-type main-sequence companion via Roche-lobe overflow. Due to their small orbital separations, typically a few solar radii, CVs exhibit short orbital periods of a few hours and display strong photometric variability. Dwarf novae are a prominent subclass of CVs and are characterised by recurrent optical outbursts with amplitudes of 2–6 magnitudes and recurrence timescales ranging from weeks to months. These outbursts are understood with the disk instability model (DIM), in which thermal–viscous instabilities in the accretion disk drive transitions between quiescent and outburst states. Dwarf novae provide an excellent laboratory for studying accretion disk physics and time-dependent disk evolution. In eclipsing systems, changes in the disk structure can be probed using eclipse depth and out-of-eclipse flux measurements. Recent high-cadence photometric studies have revealed hysteresis behaviour in eclipse fraction diagrams, indicating a temporal lag between variations in mass accretion rate and disk radius during outburst cycles. In this talk, I present an overview of cataclysmic variables with emphasis on dwarf novae, their outburst mechanisms, and observational diagnostics of accretion disk evolution. I also outline the motivation and objectives of ongoing work focused on studying the evolution of accretion disks in eclipsing dwarf novae.

Relativistic jets in blazars are sites of extreme plasma conditions, efficient non-thermal particle acceleration, and broadband radiation extending from radio to very-high-energy γ-rays. Their spectral energy distributions (SEDs) exhibit a characteristic double-humped structure, commonly interpreted as synchrotron emission at low energies and inverse-Compton or hadronic processes at high energies. The observed luminosities, rapid variability, superluminal motion, and one-sidedness of the jet impose strong constraints on the size, speed, and geometry of the emitting region, requiring relativistic beaming and compact dissipation zones within the jet. Leptonic and hadronic emission models are commonly employed to reproduce blazar SEDs and multi-wavelength variability, but these models typically rely on simplified assumptions for the underlying non-thermal particle energy distributions. Such non-thermal spectra cannot arise from purely thermal processes, indicating the presence of efficient particle acceleration operating in relativistic jet environments.

The Milky Way galaxy is our home galaxy, hosting our solar system and billions of other stars. One of the key questions in galactic astronomy is to understand the formation and evolution of galaxies. As we are part of the Milky Way, it provides us with a unique opportunity to study its components in great detail, allowing us to gain a deeper understanding of how galaxies form and evolve in general. According to the cosmological paradigm, galaxies form through hierarchical accretion of lower-mass galaxies. The recently discovered stellar streams in the Milky Way's halo are direct evidence of these merger events. Stellar streams form due to the tidal disruption of a globular cluster or dwarf galaxy that orbits the Milky Way. In this talk, I will discuss about the stellar streams, how they are detected, and what information we obtain from their spectroscopic follow-up. I will also discuss about the target selection for the spectroscopic observation of the stream stars. Determining the age of the stellar streams is crucial because they serve as a record of the Milky Way's growth, revealing its merger history and assembly timeline.

Symbiotic stars are interacting binary systems composed of a cool red giant and a hot white dwarf. Material is transferred from the giant to the dwarf through a stellar wind or in some systems,via Roche-lobe overflow. An intriguing fact of symbiotic systems is their extremely low known population; only around 300 such system are known against their predicted population of around 300,000 in our Galaxy. Moreover,these exhibit unique emission features at 6825 Å and 7082 Å, which are caused by the Raman-scattering of O VI doublet at 1032 and 1038 Å. As these features are a result of scattering, they show polarization signatures and hence can be used to probe the morphology and kinematics of the systems. We plan to undertake a long term spectro-polarimetic observational study of such systems, wherein any temporal variability of these Raman scattered features would be explored using spectro-polarimetric observations from ProtoPol instrument on PRL 2.5m telescope. In addition, we are upgrading the existing MFOSC-P instrument on PRL 1.2m telescope with newer spectro-polarimetric capabilities.

Measurements of the power spectrum of the redshifted 21-cm signal from the Epoch of Reionization (EoR) provide crucial insights into the ionization and thermal states of the intergalactic medium (IGM) and depend sensitively on the nature of the early radiation sources. Recent upper-limit constraints from SKA precursor experiments such as MWA, HERA, and LOFAR have already begun to exclude several extreme reionization models (e.g., Ghara et al. 2020, 2021). In these models, the 21-cm signal fluctuations are primarily driven by rare, large ionized or emission regions in the early Universe. With forthcoming, more stringent upper limits, particularly from small-scale power spectrum measurements by the SKA, the constraints on the IGM state during the EoR are expected to improve significantly. In this presentation, I will discuss which reionization scenarios and IGM conditions are likely to be ruled out first with SKA observations. I will also summarize the current understanding of the IGM properties during the EoR based on results from ongoing 21-cm signal experiments.

Young stars consist of a prestellar core, a circumstellar disk, and an envelope. Material from the envelope accretes to the disk, and through angular-momentum loss or removal, disk material is transported onto the central star. Circumstellar disks are therefore central to both stellar growth and planet formation, making them crucial for understanding the early stages of stellar evolution. In low-mass pre-main-sequence stars, accretion proceeds through magnetospheric funnels that channel disk material onto the stellar surface, generating accretion shocks that result in an excess emission in the UV region and strong emission lines. Classical T Tauri stars (CTTSs) show highly variable accretion across multiple timescales. The origins of this variability remain unknown. In this seminar, I will present a detailed analysis of a classical T Tauri star using multiple emission-line diagnostics to investigate its accretion properties and discuss various line diagnostics related to star-disk interaction processes.

Solar Energetic Particles (SEPs) are charged particles with energies ranging from keV to several GeV, accelerated during solar flares and CMEs. Understanding SEPs is crucial for space weather. These particles generally follow the large-scale interplanetary magnetic field, however, heliospheric magnetic turbulence repeatedly scatters them. This scattering governs SEP propagation, and diffusion parameters such as the parallel diffusion coefficient quantify the strength of diffusion along magnetic field lines. By combining X-ray spectral observations from the Solar X-ray Monitor (XSM) onboard Chandrayaan-2 with particle flux measurements from multiple spacecraft, and by modelling the particle propagation event, we experimentally determine the SEP diffusion coefficient.

As a little boy, I was already fascinated by the magnificent light show of the twinkling stars in the night sky. My scientific career started almost 30 years ago when, as a physics student at KU Leuven (Belgium), I prepared my master's thesis under the supervision of Conny Aerts. Thanks to her enthusiasm, I started to look into asteroseismology, where the stars reveal the secrets of their hidden interior through the way they vibrate. In this presentation I would like to demonstrate how my interest in stellar pulsations in combination with a few random encounters have led to the two projects that I consider my greatest scientific achievements to date, namely the close collaboration with colleagues from both China (via the LAMOST-Kepler project) and India (via the BINA project). The strength of these projects will be demonstrated by some scientific results in different domains.

Active Galactic Nuclei (AGN) are among the most luminous astronomical sources, powered by accretion of matter onto a Supermassive Black Hole (SMBH). Their X-ray emission arises from the upscattering of optical/UV photons from the accretion disk by a hot corona of relativistic electrons, producing a power-law spectrum, which is modified by absorption and reflection features. In some AGN, an excess of photons above the standard power-law can be observed below the 2 keV energy range, termed as Soft Excess. The origin of this Soft excess is still a matter of debate, and various theories have been proposed to explain this excess emission. The warm corona model attributes this emission to arise from the inverse Comptonizaton of the disk photons in an optically thick, warm (0.1 - 1 keV) corona. Alternatively, the blurred ionized reflection scenario explains the soft excess to be a result of the relativistic blurring of the reprocessed emission from the disk due to the effects of strong gravity near the SMBH. More recently, hybrid models combining both warm Comptonization and ionized reflection components have also been proposed.

Blazars are the most powerful subclass of active galactic nuclei in which observed emissions are highly Doppler boosted and observable across the entire accessible electromagnetic spectrum ranging from radio to gamma-rays, with diverse variability timescales spanning across minutes to years. The AGN activity level appears to vary on various time-scales. To date, most of the studies have focused mainly on high activity episodes, thereby offering a limited view of the source physical conditions. In our recent work we studied long-term broadband temporal and spectral study of a TeV BL Lac object TXS 0518+211 using 16 years of simultaneous optical, UV, and X-ray observations. In this blazar we find the complex nature of jet-dominated emission processes and suggest for more than one emission zone contributing to the observed broadband spectral energy distribution (SED). In this talk, I shall also present the results based on the photometric and spectroscopic observations acquired from Mt. Abu telescopes.

ProtoPol is a medium-resolution echelle spectro-polarimeter developed for the PRL 1.2m and 2.5m telescopes at Mt Abu observatory, India. ProtoPol provides a spectral resolution in the range of ∼0.4 - 0.75˚A across various orders in the visible wavelength range of 4000-9600˚A. On PRL 2.5m PRL telescope, an SNR of 10 is achieved for Vmag ∼ 13.5 source in 1 hour of integration time, and its throughput is estimated to be ∼6% including all the contributing factors such as atmospheric transmission, telescope reflectivity, instrument’s optics, CCD efficiency, etc. ProtoPol achieved a linear polarization accuracy ≈ 0.1 − 0.2% in 2 hours of integration time for a source with Vmag ≈ 8. The instrumental polarization is determined to be around 0.1%. Several Science observation campaigns were conducted with ProtoPol to demonstrate the capabilities of the instrument. A sample of Herbig Ae/Be stars, classical Be stars, Symbiotic stars, and AGB/post-AGB stars were observed over the period of one and a half years for their spectro-polarimetry measurements covering various physical mechanisms such as line polarization in Herbig and classical Be stars, polarization in Raman scattered features in Symbiotic stars, as well as continuum polarization in AGB/post-AGB stars to verify the polarization performance of the instrument.

Gamma Ray Bursts (GRB) are short, intense extragalactic gamma-ray flashes. GRBs are of two kinds-long GRBs (burst duration >2 sec) thought to be produced due to core collapse of rapidly rotating massive stars, short GRBs (duration <2 sec) believed to be produced due to merger of binary compact objects like neutron star-neutron star (NS-NS) or black hole-neutron star (BH-NS). Daksha is India’s proposed high-energy transient mission aimed at detecting and characterizing electromagnetic counterparts (EMCs) of gravitational wave (GW) events and GRBs. In its initial configuration, Daksha can localize short GRBs to within 5–10 degrees using a projection method. Daksha’s scientific potential could be greatly enhanced if onboard GRB localization within 1 degree is made possible, which can be potentially achievable using the Coded Aperture Mask (CAM).

Since its deployment to the International Space Station in June 2017, the Neutron Star Interior Composition Explorer (NICER) has significantly advanced our understanding of compact objects in the X-ray sky. With exceptional timing and spectral capabilities in the 0.2 - 12 keV range, NICER enables detailed studies of accretion-powered and magnetically driven phenomena. A major focus has been on thermonuclear X-ray bursts -brief, intense explosions caused by unstable burning of hydrogen and helium on neutron star surfaces, which offer key insights into the physics of dense matter. This talk will highlight crucial findings from eight years of NICER observations, covering burst behavior, accretion dynamics, X-ray transients, and magnetar activities. It will also discuss efforts to understand the interaction between compact objects and their optical companions through X-ray and optical observations. Finally, I will present recent updates on the long-term calibration of the JEM-X instruments aboard ESA's INTEGRAL mission and ongoing progress toward establishing the INTEGRAL Legacy Archive.

Compact objects represent some of the most extreme environments in the universe. When these dense remnants are part of a binary system, they can draw in matter from their companion stars through a process known as accretion. This transfer of material releases vast amounts of energy, making these systems strong sources of X-rays. Compact X-ray binaries, in which a neutron star or black hole accretes matter from a companion, offer unique opportunities to study energetic processes like accretion dynamics, outbursts, and thermonuclear bursts on neutron star surfaces. This talk will introduce the fundamental concepts behind accretion, compact binaries, and related phenomena, and will highlight why these systems are key to advancing our knowledge of high-energy astrophysics.

METIS, an advanced mid-infrared imager and spectrograph for the wavelength range 2.9-13.5 microns (astronomical L, M, and N-band), stands as one of the three science instruments at the Extremely Large Telescope (ELT). It will provide diffraction-limited imaging, coronagraphy, high-resolution integral field spectroscopy, and low and medium-resolution slit spectroscopy. Within the collaborative international METIS consortium, the University of Cologne is responsible for the design, manufacturing, and integration of the Warm Calibration Unit (WCU) of the instrument. The main role of WCU is to provide a stable and controllable reference signal to METIS that will allow troubleshooting and calibrating the response of METIS in various observing modes. In this talk, I will present the key requirements from METIS that drive the design of the WCU, followed by an overview of its optical and opto-mechanical design, and functional role within the instrument. The final part of the presentation will focus on the current status of the Manufacturing, Assembly, Integration, and Testing (MAIT) phase, including a brief discussion on the alignment verification plans for the offner relay optics of WCU.

Accretion-powered X-ray pulsars (XRPs) are magnetized neutron stars that are part of X-ray binary (XRB) systems. The XRPs emit X-rays by accreting mass from their binary companion. These pulsars are characterized by intense magnetic fields, typically ranging from ~ 10^12-10^14 G, which direct the infalling material toward their magnetic poles, where most X-ray photons are generated. When the magnetic and spin axes are misaligned, the resulting emission is observed as pulsations from the neutron star. RX J0032.9-7348, an X-ray transient, was first detected by ROSAT in 1993; however, its properties are largely unknown. After years of inactivity, the source entered an X-ray bright phase in 2024. We observed it during this phase using NuSTAR and NICER. In this talk, I will present the timing and spectral properties of RX J0032.9-7348 during its 2024 outburst and discuss our ongoing and future work.

Hot and variable stellar populations in star clusters such as blue straggler stars (BSSs), blue lurkers, horizontal branch (HB) stars, and white dwarfs (WDs) offer critical insights into stellar evolution, binary interaction mechanisms and the dynamical evolution of stellar systems. In this talk, I will shed light on the characteristics and formation pathways of these non-canonical stars with a few case studies. I will discuss the detection of extremely low-mass white dwarfs (ELM WDs) as companions in BSS binary systems in Globular cluster NGC 362. In NGC 362, the radial distribution of BSSs exhibits strong central concentration, classifying the cluster as dynamically evolved and likely in a post-core-collapse phase. We also report the first identification of blue lurkers in a globular cluster. Two-component SED modeling reveals their companions to be low-mass and ELM WDs with short cooling ages (< 4 Myr), suggesting a recent formation event likely triggered by dynamical interactions during core collapse. In addition, we identify high-mass WDs in NGC 362, which may have originated via white dwarf–white dwarf mergers, a rare but theoretically predicted evolutionary channel in dense stellar environments. In the open cluster NGC 2420, four binary systems were identified, including two BSS binaries, one BSS–ELM WD system, and one HB–ELM WD system. These systems are consistent with formation via Case A/B mass-transfer pathways, indicative of stable binary evolution in low-density environments. Ongoing time-series photometric analysis has led to the identification of multiple variable stars, including pulsating and eclipsing systems, particularly among the BSS and HB populations. These variables provide independent diagnostics of internal stellar structure, angular momentum evolution, and rotational modulation. I will also discuss the ongoing spectroscopic analysis of BSS–RGB binary systems to further constrain the mass-transfer origin of BSSs, for understanding the role of binary evolution in shaping the hot stellar populations observed in star clusters.

Observational data show strong correlations between the mass of supermassive black holes and the properties of their host galaxies, leading to the idea of SMBH-galaxy co-evolution. Galaxy mergers are interesting events as gravitational torques during mergers drive gas towards galactic nuclei, which can enhance AGN activities. This leads one to question: to what extent do mergers enhance AGN activities compared to isolated galaxies, and how does this impact the galactic environment? In this talk, I shall elaborate on our efforts to answer this question by introducing Stars and MUltiphase Gas GaLaxiEs (SMUGGLE), a framework based on the hydrodynamic code AREPO with a multiphase interstellar medium. I shall talk about the limitations of traditional simulations, improvements in SMUGGLE, and other simulation specifications. Our efforts in characterizing the duty cycles of AGNs and dual AGNs during mergers have shown that Multiphase ISM in SMUGGLE yields highly variable accretion rates with short duty cycles. In mergers, the mean active phase timescales are in the order of 0.1 Myr to 1 Myr, and dual AGNs seem to be active for 10-20 per cent of the simulation time before the black holes merge. Differences in black hole masses, galaxy morphologies, and wind speeds do show a significant impact on AGN and dual AGN activities. I shall conclude with a summary of current results, as well as ongoing and future work.

Solar flares are among the most energetic phenomena in the solar system, driving rapid restructuring of magnetic fields and heating across the solar atmosphere. While much progress has been made in understanding flares through observations in X-rays and extreme ultraviolet (EUV), the near-ultraviolet (NUV) range remains relatively unexplored—despite its sensitivity to key layers like the lower chromosphere and upper photosphere, where much of the flare energy is deposited. The Solar Ultraviolet Imaging Telescope (SUIT), onboard India’s Aditya-L1 mission, is the first instrument to provide full-disk solar imaging in multiple NUV passbands, opening a new window into this critical regime. In this talk, I will first outline the current state of flare research and highlight the observational and diagnostic gaps that exist in the NUV. I will then introduce SUIT’s science objectives in the context of these challenges. As part of my PhD, I contributed to the initial design of SUIT. I will also present our first results from SUIT, and discuss how these data can inform models of chromospheric heating and flare energy transport. This work sets the stage for SUIT’s long-term contribution to high-cadence, multi-height solar flare studies.

I will present a systematic study of exotic stellar populations-Blue Stragglers (BSS) and Extreme Horizontal Branch (EHB) stars-in dense environments of the Milky Way and satellite dwarf galaxies. Despite decades of research, their formation channels, binary companions, and chemical evolution remains poorly understood due to their diverse properties across different environments. These UV-bright objects have now become accessible through new facilities like AstroSat/UVIT and public catalogs, revealing previously unknown extreme systems that challenge existing stellar models. To resolve these puzzles, I propose a coordinated multi-wavelength campaign utilizing high and medium-resolution spectroscopy (ground-based optical/infrared observatories), UV diagnostics (HST, UVIT/AstroSat, Swift/UVOT), and astrometry (Gaia and HST). This approach will uncover binary interactions, atmospheric anomalies, and evolutionary pathways-providing critical insights into stellar rejuvenation mechanisms and revealing new characteristics of these stellar populations.

Abstract - Galaxies are the building blocks of the Universe, and some of the most massive and mysterious ones formed when the Universe was just a few billion years old. Many of these early galaxies were rich in dust and forming stars at high rates, yet hidden from view in visible light. These dusty star-forming galaxies (DSFGs) played a key role in building today’s giant elliptical galaxies, and understanding them is essential to piecing together the story of galaxy formation. In my recent work, I used data from space and ground-based telescopes (JWST, Euclid, Herschel, and LSST) to show how we can trace the stars, dust, and AGN activity in these galaxies across cosmic time, and developed physical models. In this talk, I shall demonstrated that by combining multi-wavelength data (from ultraviolet to far-infrared) we can get a complete picture of how galaxies evolve, even when they are deeply buried in dust. I shall also discuss the role deep radio surveys in unveiling obscured active galactic nuclei (AGN) at high redshifts.

The habitability of any planet is decided by a complex evolution of its interior and atmosphere. Recently in many observations, it has been found that close-in exoplanets are going through significant atmospheric evaporation, which could affect the overall evolution of the exoplanet atmosphere. This atmospheric evaporation from exoplanets is very much dependent on the plasma and radiation environment of their parent stars (e.g., stellar radiation, stellar wind, stellar flares, and Coronal Mass Ejections (CMEs). In this talk, I will explain different physical processes (e.g., Jeans escape, hydrodynamic escape) by which an exoplanet can lose its atmosphere. One major process that leads to significant loss of exoplanetary atmosphere is the stellar radiation-driven atmospheric outflow. Once planetary outflow is initiated from the planet by stellar radiation, it further interacts with the stellar wind shaping up the exoplanetary atmosphere (sometimes producing a comet-like structure) and its atmospheric mass-loss rate. Moreover, flares and coronal mass ejections (CMEs) from the star will also have a great impact on planetary evaporation and mass loss. I will present our newly developed 3D radiation magnetohydrodynamics model where we have implemented a self-consistent radiative transfer of incident stellar radiation to simulate planetary outflow and its interaction with the stellar wind, CMEs, and flares. I will show that radiation-driven planetary outflow alone can not explain the observed transit signatures & corresponding mass-loss rate, but the interaction with the stellar wind/coronal mass ejections can explain the observed mass-loss rate and transit for many exoplanets. I will also discuss briefly the effect of stellar and planetary magnetic fields on the atmospheric mass-loss rate and corresponding observational signatures.

Blazar flares offer a unique window into the extreme physics of relativistic outflows, including particle acceleration and the origin of multi-wavelength (MWL) emission. A key approach to studying these processes is physical modeling of varying blazar jet emission. Many numerical codes employ a kinetic framework to track particle spectrum evolution under various physical effects. We have developed EMBLEM (Evolutionary Modeling of BLob EMission), a versatile radiative code based on time-dependent particle (re-)acceleration, escape, radiative cooling, and adiabatic expansion. This code allows us to self-consistently connect low state and flaring emission. Based on a leptonic framework, the code incorporates synchrotron self-Compton (SSC) and external Compton (EC) scenarios. We showcase its application to (1) modeling extreme gamma-ray flares in blazars such as Mrk 421 and 3C 279, and (2) searching for internal gamma-ray opacity signatures in high-redshift blazars.

Cataclysmic Variables (CVs) are examples of semi-detached binary star systems characterized by the flow of stellar material from the companion star to the primary (white dwarf). If the primary possesses a significant magnetic field, the accretion dynamics can be drastically altered. In particular, polar magnetic CVs, characterized by their strong magnetic fields are often marked by the lack of an accretion disk and also exhibit unique observational signatures, such as highly polarized radiation, synchronous rotation, etc. In this talk, I will discuss the properties of these high field systems and the interaction between the magnetic field and the accretion flow which can lead to complex phenomena, including emission of X-rays and cyclotron radiation. I will then explain some methods used to probe the magnetic field in such systems. I will also discuss the identification of potential high field systems from a sample of CV candidates from the 5th data release of the LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope) spectroscopic survey. I will conclude my talk by presenting an estimate for the magnetic field in LAMOST J003553.36+433341.4 from its LAMOST spectrum.

Comets are the preserved minor bodies which holds the primitive information about the early solar system. These bodies come into the inner solar system from two reservoirs, i.e., Kuiper Belt and Oort Cloud. Kuiper Belt is the source of Short-Period, low-inclination comets (SPCs) whereas Oort Cloud is the source of Long-Period Comets (LPCs) having isotropic inclination. Dynamically New Comets (DNC) are a long-period comets, with a semi-major axis > 10000 AU, entering the inner Solar System for the first time, which gives us an excellent opportunity to study their composition and origin. In this talk, I will explain the early classification for comets based on the basis of different dynamical and chemical properties. I will then explain the origin of a few long-period comets using the N-body dynamical simulation package, REBOUND. I will explain the N-body simulation code and benchmarking test with the well known asteroid, APOPHIS. I will conclude my talk with the inclusion of Non-gravitational forces and the difference with the results.

Direct imaging of rocky exoplanets remains a major scientific objective for current and next-generation large telescopes. While existing facilities have successfully imaged young, Jupiter-mass exoplanets at wide separations (>0.1"), detecting smaller, rocky planets poses a significantly greater challenge due to the stringent contrast requirements. The mid-infrared (mid-IR) regime offers a promising solution, providing optimal planet-star contrast for detecting thermal emissions from exoplanets in our solar neighbourhood. In this talk, I will discuss the key techniques enabling direct imaging of exoplanets, with a focus on two mid-IR high-contrast imaging (HCI) instruments: NEAR (New Earths in the Alpha Cen Region) and METIS (Mid-infrared ELT Imager and Spectrograph). The NEAR experiment demonstrates the feasibility of HCI at ten microns, achieving sub-mJy sensitivity within a few hours—sufficient to detect multiple Jupiter-mass planets around nearby stars. I will present its operational principles and scientific outcomes. Furthermore, I will explore METIS, the first-generation instrument for the Extremely Large Telescope (ELT), highlighting its HCI capabilities and expected performance.

Active galactic nuclei (AGNs) are the most luminous and energetic sources in the universe, powered by the accretion of matter onto supermassive black holes (SMBHs) located at the centers of host galaxies. The soft excess refers to an enhancement of flux in the soft X-ray range (below∼2 keV) over the primary power-law continuum, commonly observed in most Seyfert 1 AGNs. Its origin is a long-standing and unsolved puzzle in AGN studies. To investigate this, we conducted an extensive temporal and spectral analysis of the Seyfert 1 AGN Mrk 50, utilizing the observations from XMM, Swift, and NuSTAR. Two possible physical scenarios explain the origin of soft excess in AGNs , Warm Comptonization and Reflection from the ionized accretion disk. Both physical models successfully explained this behaviour in Mrk 50. Further, we investigated the origin using a model-independent approach using cross-correlation analysis between two X-ray bands (soft and hard) to examine the correlations and delays between them. In this seminar, I will present a detailed study of the origin of the soft excess in Mrk 50, based on our temporal and spectral analysis.

This presentation highlights the core components of my doctoral research, which focused on the photometric and spectroscopic characterisation of Type II core-collapse supernovae (CCSNe) and the development of automated data processing tools for time-domain surveys. CCSNe are end stages of massive stars, contributing to the chemical enrichment of the interstellar medium and influencing galaxy evolution through the dispersal of heavy elements. I conducted detailed observational studies of two transitional SNe—2020aze and 2020jfo—which do not fit cleanly into the classical Type IIP or Type IIL categories. SN 2020jfo exhibited a shorter plateau duration but shared key properties with Type IIP SNe. At the same time, SN 2020aze displayed characteristics that were more aligned with Type IIL SNe, including early flash features and a faster decline during the photospheric phase. These analyses contribute to the growing understanding that Type IIP and IIL SNe form a continuum rather than distinct classes. To investigate te role of progenitor environments, I conducted a statistical study on a broader sample of SNe by estimating metallicities using Fe line equivalent widths. This analysis provided insights into how progenitor metallicity influences light curve morphology and explosion characteristics. Complementing the observational work, I developed a fully automated aperture photometric pipeline in Python for the 4.0m International Liquid Mirror Telescope (ILMT). The pipeline processes time-delay integration (TDI) mode data, performs astrometric calibration, computes instrumental magnitudes, and derives calibrated light curves using catalogues like Pan-STARRS and SDSS. The pipeline is fully functional and is being used to derive long term light curves of variable sources.

Neutron stars (NSs) are ultra-dense remnants of massive stars, characterized by immense gravitational fields, temperatures, and densities, making them unique laboratories for studying matter under extreme conditions. Type-I X-ray bursts, observed from accreting NSs in low-mass X-ray binary systems, provide valuable insights into these environments. These bursts are driven by unstable thermonuclear burning of accreted hydrogen and/or helium on the NS surface, typically lasting from tens to hundreds of seconds, depending on the fuel composition. About 20% of these bursts are energetic enough to temporarily lift the NS photosphere by tens to hundreds of kilometers. Additionally, the nuclear burning during the bursts leads to the synthesis of elements as heavy as those in the Sn-Sb-Te mass region. Studying these events offers critical information about nuclear processes, burst-accretion disk interactions, and provides important constraints on NS properties such as spin and compactness. Observations from the Neutron Star Interior Composition Explorer (NICER) have advanced our understanding by offering unprecedented timing and good spectral sensitivity, enabling detailed studies of X-ray bursters. This talk will focus on the latest NICER findings, highlighting the complex interplay between X-ray bursts, accretion dynamics, and nucleosynthesis, and how these observations can help constrain the equation of state of NSs - the "holy grail" of NS physics.

Accreting neutron stars and black holes in X-ray binaries are powerful laboratories for exploring extreme physical conditions such as strong gravity, dense matter, and intense magnetic fields. In this talk, I will present recent discoveries from fast X-ray timing and spectral observations, including coherent and incoherent variability that reveals the nature of the innermost regions of these systems. Drawing on results from the AstroSat survey, I will highlight the discovery of an intermittent accretion-powered millisecond X-ray pulsar (AMXP)—a transient source and potential gravitational wave emitter. I will also explore the role of transient events, such as outbursts, in advancing our understanding of accretion processes and how multi-wavelength campaigns help capture the dynamic behavior of both neutron star and black hole systems. Finally, I will discuss the potential of combining X-ray polarization with timing-spectral and multi-band observations to build a more complete picture of both persistent and transient accreting compact objects.

Wide field of view (FOV) imaging X-ray telescopes play a crucial role in addressing some of the most challenging and unresolved questions in modern astrophysics. For example, they are crucial for probing the early formation of supermassive black holes (SMBH), rigorously testing the hypothesis that nanoflares are the primary mechanism sustaining coronal temperatures above million Kelvin, and detecting the electromagnetic counterparts of gravitational wave events. However, existing optical designs for X-ray telescopes, such as the Wolter type-1 (W1) and Wolter-Schwarzschild (WS) configurations, offer high angular resolution only along the optical axis and are therefore limited to narrow FOVs (a few arcminutes), while the scientific cases mentioned above require high angular resolution across a much wider FOV (up to 60 arcminutes). In this talk, I will introduce a new optical design, the field-angle optimized (FO) design, specifically developed for wide FOV X-ray imaging telescopes. I will discuss the methodology behind this design, compare its performance with existing optical designs, and explore its feasibility for implementation in wide FOV solar X-ray telescopes.

Blazars often exhibit random, aperiodic, and stochastic behaviours in their flux across all observational electromagnetic (EM) bands over a wide range of timescales. However, the underlying causes are not yet fully understood regarding which flux variations on the intra-day/day timescales are most poorly comprehended. These variations are primarily related to accretion or jet physics, as jets are powered by accretion. In the talk, I will elucidate my findings that include the quasi-periodic oscillatory signatures and flare episodes detected in three individual Blazar candidates observed with Transiting Exoplanet Survey Satellite (TESS).

The world faces a significant gender gap in science. In Africa, in average the population of female scientists is below 25%. The African Network of Women in Astronomy (AfNWA) is an initiative that aims to connect women (or people who identify as such) working in astronomy and related fields in Africa. It was established in September 2020 as one of the committees of the African Astronomical Society (AfAS). With AfNWA we want to ensure the future participation of girls and women at all levels in the development of astronomy and science in Africa. Our main goals are to improve the status of women in science in Africa and to use astronomy to empower girls and women, and to inspire more girls to pursue Science, Technology, Engineering and Mathematics (STEM). This talk will summarise the activities carried out by AfNWA and the current status of women in astronomy in Africa. It aims to give visibility to the work and achievements of the AfNWA community, and the various activities carried out across the continent to support girls and women living and working in under-represented communities through astronomy. In Ethiopia, only about 13% of all scientists are women, and this fraction is even lower when considering the fundamental sciences. Girls avoid choosing STEM mainly due to a lack of support and/or information. This becomes even more evident when going to remote areas, where 80% of the Ethiopian population lives. The SciGirls project aims to improve the gender gap in science in the long-term by empowering female secondary school students and their female science teachers who are working and living in remote and rural areas through astronomy and its multidisciplinarity. In 2022 and 2024 we organised a carefully designed capacity-building workshop for 60 participants across Ethiopia, with the aim of training future STEM advocates in rural and remote areas. The girls and teachers carried out different activities in their communities after the training. Most of participants came from the regions that have been severely affected by conflicts over the past 4 years. SciGirls is one of the 2022 and 2024 projects funded by OAD. During this talk, we will share valuable experiences we have gained through interaction with girls and female teachers who work and live in very harsh conditions, where they rarely have any external support to fulfill their dreams. The SciGirls approach has so far yielded very positive results and the project can serve as a model also in other countries.

Gamma-Ray Bursts (GRBs) are the brightest explosions in the Universe since the Big Bang. We have comprehensive knowledge about the GRBs, but there are many open questions even after fifty years of the first detected GRB, especially about the prompt emission phase. The detection of gamma-ray burst GRB 170817A by Fermi-GBM, coinciding with gravitational wave (GW) GW170817, is one of the extraordinary discoveries in the history of the multimessenger era. It is not only the first binary neutron star (BNS) merger detected by the advanced (LIGO-Virgo) GW detectors; it is the only GW detection with a confirmed electromagnetic (EM) counterpart. The Fermi Gamma-ray Burst Monitor (GBM) is an all sky monitoring instrument sensitive to photon energies from 8 keV to 40 MeV. Its capabilities makes it ideal for providing simultaneous gamma-ray observations of gravitational-wave transients. Fermi-GBM continues to look for similar multimessenger detections through on-board triggers as well as subthreshold searches for weak transients, performed both in high-time-resolution continuous data and in targeted follow-ups of gravitational-wave events. In this talk, I will present an overview of GRBs and recent results from targeted and subthreshold searches as a counterpart of GW events.

Since the discovery of the first exoplanet, 51 Pegasi b, Hot Jupiters (HJs)—Jupiter-like exoplanets orbiting close to their host stars—have remained a central focus in exoplanetary science. Unlike planets in our solar system, these unique systems allow us to study them directly through their infrared emission. Due to intense stellar irradiation, Hot Jupiters exhibit extremely high temperatures, resulting in distinct emission spectra originating primarily from their day-side hemispheres, especially in tidally locked systems. Analyzing these emission spectra provides valuable insights into the temperature structure and chemical composition of these intriguing exoplanets. However, the overlap between planetary and stellar emissions poses a persistent challenge for planetary atmospheric modeling. Additionally, the strong day-night atmospheric flow, driven by the extreme temperature contrast between hemispheres, introduces variability in the observed emission spectra. Another intriguing feature of Hot Jupiters is their larger observed radii compared to Jupiter; a phenomenon known as the radius inflation problem. In this talk, I will explore these fascinating questions surrounding Hot Jupiters, using fundamental physics concepts to unravel the mysteries of these extraordinary worlds.

Although more than 5000 exoplanets have been detected, only a few have had their profiles constructed. Besides the radius, mass is significant variable as well, which makes the radial velocity (RV) method important. Yet, instruments and calibration of the equipment pose constraints when it comes to the detection of small Doppler shifts (sub-m/s). One such issue is the accuracy of the wavelength calibration itself. Addressing this, the cost-effective and stable Fabry-Pérot (FP) etalons are an alternative to uranium-argon (UAr) lamps because they last significantly longer and have a spectrum that is ideal for supporting better wavelength calibration for very precise RV measurements. We are changing PARAS-2’s calibration system from UAr to FP. In this seminar, we will give project progress report and show laboratory testing outcomes of the FP system.

The Sun's outer atmosphere, known as the corona, is significantly hotter than its surface, presenting a long-standing scientific mystery. One hypothesis is that small, frequent bursts of energy, called nanoflares, may be responsible for this heating, though the exact mechanism remains unclear. Additionally, certain elements in the corona appear more abundant than expected, a phenomenon termed the "FIP effect," which might also be linked to coronal heating processes. Imaging X-ray spectroscopy offers a powerful method for investigating these solar mysteries. In this talk, we will explore these intriguing questions about the Sun and discuss how imaging X-ray spectroscopy can provide insights. We will introduce the Marshall Grazing Incidence X-ray Imaging Spectrometer (MaGIXS) sounding rocket experiment and its recent successful flight, designed to probe these enigmatic aspects of the Sun.

Diffuse interstellar bands (DIBs) are interstellar absorption features originating from the interstellar medium, quasi-consensually attributed to large organic molecules. DIBs exist in the optical and in the infrared. Most of the DIBs show a tight relation with interstellar reddening, and can therefore be used as an excellent tracer of the ISM. Beside the equivalent width of the DIBs, radial velocities profiles can be derived and be used to study e.g the Galactic rotation curve of the carrier. I will present the capacity of the Gaia-Radial Velocity Spectrometer (RVS) in Gaia DR3 to reveal the spatial distribution of the unknown molecular species responsible for the most prominent DIB at 862\,nm in the RVS passband exploring the Galactic interstellar medium within a few kiloparsecs from the Sun. Nearly 500.000 DIB measurements have been obtained in a homogeneous way covering the entire sky, making it the largest sample of DIB measurements so far. I compare spatial distributions of the DIB carrier with interstellar reddening and find evidence that DIB carriers are present in a local bubble

The origins and distribution of chemical elements in the Universe have long been a subject of investigation, with many unresolved questions remaining. The oldest stars in our Milky Way are rare relics from the early Universe, preserving the chemical imprints of the first stars and supernova explosions. These stars are crucial in addressing questions about element formation processes that occurred around 13 billion years ago. I will explain on how I employ "Stellar Archaeology": the use of observations and analysis of the chemical properties of the oldest stars in Galaxy, to answer outstanding questions about the early Universe and the origins of the chemical elements in the Cosmos. One of the significant unanswered questions in astrophysics is the site of the rapid neutron-capture process (r-process). While the optical counterpart AT 2017gfo of the kilonova GW 170817 did provide evidence of the r-process in neutron star mergers, important details are still unsolved. Neutron star mergers alone seem to be unable to explain r-process enrichment in the Universe, and there are still open questions with respect to their time scale. I will discuss some of the results from observations of r-process stars with the Gran Telescopio Canarias (GTC) and the Very Large Telescope (VLT), as well as CEMP-r/s stars observed with the KECK telescope and VLT. Additionally, I will share findings from the HESP-GOMPA survey conducted by our group. Finally, I will discuss how my expertise aligns with the facilities at the Physical Research Laboratory (PRL), such as PARAS-2.

The timing and spectral studies have been carried out for several X-ray pulsars to probe the emission mechanism, accretion process, and spectral states. The timing and spectral properties evolve significantly above the critical luminosity. The accretion mode, beaming patterns, and emission mechanism evolve significantly above this luminosity. A significant evolution of temporal and spectral properties is observed during the state transition for X-ray pulsars, 1A 0535+262 and RX J0440.9+4431. A variable cyclotron line was detected from 1A 0535+26, and the magnetic field was estimated using the cyclotron line energy. The variation of the cyclotron line is probed. The significant evolution of line energy with luminosity was observed, which may be linked with the transition of state in the X-ray pulsars. The unstable burning of accreted material on the surface of neutron stars induces thermonuclear (Type-I) bursts. Thermonuclear bursts can be used to probe several properties of neutron stars. Multiple thermonuclear bursts were detected from MAXI J1816−195 and Aql X-1. The details of timing and spectral properties are studied during the X-ray bursts. The estimated mass accretion rate indicates the stable burning of hydrogen via a hot CNO cycle during the bursts.

The galaxies and star formation we see at present are attributed to a long history of galaxy formation and evolution. Reconstructing back in time the physical processes that led to the existing galaxies and explaining them in terms of different properties of the matter is one of the prime goals of the observational cosmology. In particular, studying the molecular gas content of high-redshift dusty star-forming galaxies (DSFGs) is of utmost importance for observationally confirming the galaxy formation and evolution theories. Observing the gas with low excitation leads to better mass estimates and also helps in deriving the gas and dust properties of these galaxies more accurately. Having a large and diverse sample of DSFGs for such a study plays an important role in setting up statistically significant trends within the DSFG population and in determining whether or not there are significant differences in the gas properties of DSFGs compared to other populations. This talk will be focused on the VLA large program to observe CO (1–0) in high-redshift DSFGs (0.8 < z < 6.5) for deriving insights on the cosmic star formation history.

Star formation is a fundamental and vital process of molecular cloud evolution and the creation of stellar systems. Stars are born within the dense, compact, and low-temperature regions of molecular clouds called cores. These dense cores are the sites that eventually lead to the formation of a protostar, surrounded by a protoplanetary disc and an infalling envelope. Understanding the various stages, from the collapsing cores to the formation and growth of a protostar, requires understanding the physical and dynamic processes involved. In this talk, I will discuss the various stages of star formation and the role of different physical processes involved and also touch upon the evolution of a protoplanetary disk and the accretion from the disk to the star.

The lower solar corona exhibits significant dynamic activity across various scales, with magnetic features continuously forming and disappearing on the Sun's surface. Understanding the relationship between these features and the heliosphere is crucial for understanding the heliosphere and predicting the flow of plasma within it. This knowledge is essential for forecasting space weather accurately. In this study, we investigate an M-class solar flare from which plasma eventually propagated into the heliosphere. We examine the evolution of First Ionization Potential (FIP) elements during the flare using the soft X-ray spectrum from the Solar X-ray Monitor aboard Chandrayaan-2. Additionally, we analyse in situ particle data to determine whether the evolution of FIP elements can be observed at 1 AU or other heliospheric locations.

Over the past decade, Spitzer and Herschel observations have provided invaluable opportunities to explore key structures in star-forming regions, such as bubbles and filaments. With the advent of the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA), researchers have access to a powerful multi-wavelength approach, which can be used to investigate the dust and gas structures around embedded protostars in exceptional detail and to study distant star-forming sites. We present an observational study of the S284-RE region (d ~5.0 kpc), a low-metallicity area associated with the extended S284 HII region. The S284 region is characterized by features such as filaments, pillars, and globules, which are hallmarks of star-forming regions shaped by stellar feedback. Multi-scale and multi-wavelength datasets are used to explore the underlying physical structures and protostellar activities in this site. In this talk, I will provide a detailed overview of our findings and their implications for understanding the physical processes driving star formation in S284-RE.

The discovery of exoplanets has revealed numerous planetary populations with no analogs in the Solar System. Among these, sub-Saturn exoplanets, larger than Neptune but smaller than Saturn and in close orbits around their host stars, represent a particularly intriguing class. Sub-Saturns are often described as failed gas giants, possessing equally massive cores but significantly smaller total masses due to their much smaller accreted envelopes. In this talk, I will discuss our recent discovery of a sub-Saturn TOI-6038 A b using PARAS-2 spectroscopic observations. TOI-6038 A b is a relatively dense sub-Saturn with a mass of approx 79 Earth masses and a size of about 6.4 Earth radii, orbiting a bright, metal-rich late F-type star in a nearly circular orbit with a period of about 5.83 days. The system also contains a wide-orbit binary companion, TOI-6038 B, which is an early K-type star at a projected separation of 3217 AU. Internal structure modeling indicates that about 74% of the planet’s mass is made up of rocky materials forming the core, with the rest consisting of a low-density H/He envelope. TOI-6038 A b lies in the transition zone between the Neptunian ridge and savanna, making it a key system for understanding the formation and evolution of close-in sub-Saturns. While its high density is consistent with planets shaped by high-eccentricity tidal migration, the exact migration pathway remains unclear. The planet’s bright host star makes it a promising candidate for future atmospheric escape and orbital architecture observations, which will help us better understand its overall evolution.

Active Galactic Nuclei (AGN) are among the most energetic and luminous astronomical sources in the Universe. With bolometric luminosities reaching up to Lbol = 1048 erg s−1 (or 1015 L⊙), the AGNs emit across the entire range of the electromagnetic spectrum. The central source in an AGN is thought to be a supermassive black hole actively accreting nearby matter through an accretion disk, releasing substantial energy in the process. In this talk, I will provide an overview of various components of an AGN that account for its distinctive features across different regions of the electromagnetic spectrum. Emphasis is placed on the X-ray spectrum of the AGN, which offers crucial insights into the energetic processes close to the central engine. Finally, I will discuss the Unified Model of AGNs, which explains how diverse astronomical objects - such as Seyfert galaxies, quasars, radio galaxies - fit under the overarching category of AGN, despite differing in their observational characteristics.

Gamma ray bursts (GRBs) are the intense extragalactic gamma ray flashes which last for a few milliseconds to a few hundreds of seconds. The simultaneous detection of both the gravitational wave (GW) and electromagnetic (EM) signals is the only way to probe the origin of short GRBs (flash duration<2s). Hence both sensitivity of GW and EM detectors is essential in addition to all sky coverage of EM detectors. Daksha is a proposed high energy transient mission of India providing full sky coverage with better sensitivity whose primary goal is to detect electromagnetic counterparts of gravitational wave events. In addition to the sensitivity of EM detectors, precise localisation of events is very crucial for their follow up afterglow study in other EM wave bands. The short GRB afterglow study is important since it carries signatures of elements heavier than iron formed from r-process nucleosynthesis of neutrons in the ejecta of BNS merger, also many fundamental physics can be verified from the signatures carried by these events at high redshifts. The proposed Daksha configuration estimates localization based on the ratio of photon counts on detectors at different orientations. In this work we explore the improvement of localization in Daksha if a coded mask is used for either low or medium energy detectors. For this, we have estimated both sensitivity and localization accuracy of Daksha detectors.

Star clusters are ideal places to explore the formation and evolution of stellar systems. They host stars of almost all the evolutionary phases. Mostly, young and massive stars dominate the open clusters, whereas the globular cluster traces the evolutionary sequence of low-mass stars. They also contain exotic stellar populations (e.g., blue straggler stars, blue hook stars, AGB-manque stars, low mass He white dwarf, and catalysis variables, etc.), which are byproducts of dense stellar environments and/or binary stellar systems in the cluster. The ultraviolet (UV) emission in star clusters is mostly dominated by the young (massive), exotic, and evolved stars, which are important to studying the formation and evolution of a star cluster. I will present the first comprehensive ultraviolet (UV) source catalogue (UVIT DR1) of UV photometry in various FUV (1300−1800 A) and NUV (2000−3000 A) filters of the UltraViolet Imaging Telescope (UVIT) onboard AstroSat. UVIT DR1 includes a total of 239,520 unique UV-bright sources, of which 70,488 sources have FUV magnitudes, and 211,410 have NUV magnitudes covering a sky area of ~ 58 sq. deg. I will showcase the results of a newly discovered hot post-AGB star in a sparse Galactic globular cluster, E3 (ESO 37-1), using UVIT observations. I will discuss its binarity, chemical abundance and evolutionary status utilizing observed/archival datasets of the UVIT/AstroSat, Gaia DR3, and high-resolution spectra. In this talk, I will also discuss the preliminary results of the study of blue straggler stars in selected star clusters using photometric and spectroscopic observations of the 2.5m telescope, Mt. Abu.

More than 150 high-significance gravitational wave (GW) sources, primarily binary black hole mergers, have been detected by ground-based GW observatories to date. The joint GW and EM detections of the binary neutron star merger GW170817 yielded a scientific bonanza in fields as wide-ranging as gravitational physics, nucleosynthesis, neutron star equation of state, relativistic explosions and jets, and cosmology. The EM counterpart of GW170817 gave insight into the mass, speed and composition of the slow-moving merger ejecta through the rapidly-evolving kilonova emission (from r-process nucleosynthesis), while the long-lasting afterglow probed the energetics and morphology of the relativistic ejecta (jet and cocoon). It also provided an unambiguous link between neutron star mergers and short gamma-ray bursts, and facilitated a precise measurement of the Hubble's constant. I will discuss the astrophysics and fundamental physics learned from GW170817 and what could be learned from future GW events: like NS-NS and NS-BH mergers. I will also describe the searches for systems like NS-BH and high-mass-ratio systems in the Galactic Center that will be important for space-based detectors like LISA.

The three-body problem describes the motion of three objects under the influence of their mutual gravity. It is one of the oldest problems in astrophysics. No closed form analytical solution is possible to the general three body problem due to its chaotic nature. Despite its rich history, the three-body problem remains an active area of research. Recent advancements in the field are motivated by new discoveries pertaining to exoplanets and blackholes. In this work we focus on resonant and secular interactions in three body systems, with a goal to understand how these interactions influence the long-term stability and evolution of three body systems. We apply our theoretical investigations of these physical processes to a wide range of observed systems. We find that secular and resonant perturbations can significantly affect the stability limit of mutually inclined planets. Planets in retrograde configurations are much more stable than prograde configurations, with secular perturbations significantly destabilizing the system when 200 < Imut < 1600. In addition, we find that secular three body dynamics can also help us constraint the inclination of the hypothetical Planet-9 in the outer solar system, and explain the observed retrograde stellar obliquities of hot Jupiters. We also propose a novel pathway through which compact binaries could merge due to eccentricity excitation caused by resonant interactions induced by a massive coplanar companion. Specifically, a compact binary migrating in an AGN disk could be captured in a precession-induced resonance, when the apsidial and nodal precession rates of the binary are commensurable to the orbital period around the supermassive black hole. Eccentricity is excited when the binary sweeps through the resonance which happens only when it migrates on a timescale 10-100 times the libration timescale of the resonance. The eccentricity excitation of the binary can reduce the merger timescale by a factor up to 103 -105.

Eclipsing binaries (EBs) are essential for understanding stellar evolution, providing direct measurements of stellar masses, radii, and luminosities. Among these, W UMa-type systems, also known as contact binaries, are particularly important because the stars share a common envelope, leading to complex energy exchanges. W Uma-type systems are important as they give information about component interactions, mass-trasfer between components, period evolution, extra bodies around inner binary etc. In this talk, I will present a long-term photometric and spectroscopic analysis of four W UMa-type systems. This study combines light curves with spectroscopic data, revealing details about their orbital parameters, period changes, and evolution. The findings shed light on the internal dynamics of contact binaries, offering valuable insights into stellar interaction and evolution. I will discuss the methods used, the findings, and their significance in the broader context of contact binaries.

ProtoPol is a medium-resolution echelle spectro-polarimeter initially conceived as the prototype instrument of the currently under development M-FOSC-EP (Mt. Abu Faint Object Spectrograph and Camera-Echelle Polarimeter) instrument – a two-channel multimode instrument which is currently being designed for PRL 2.5m telescope at Mt. Abu. Though ProtoPol was initially conceived to evaluate the development methodology of M-FOSC-EP using commercially available off-the-shelf components, it was later elevated to the level of a full-fledged back-end instrument for PRL telescopes. ProtoPol was designed on the concept of echelle and cross-disperser gratings to record the cross-dispersed spectra in the wavelength range from 390 to 940 nm with a resolution in the range of 7000-8000. ProtoPol has been successfully developed and commissioned on PRL 1.2m and 2.5m telescopes since December 2023, and a variety of observations are being carried out for instrument characterization and scientific purposes. In this talk, I shall discuss the features and properties of ProtoPol, the assembly-integration-testing of the instrument in the laboratory, and its subsequent commissioning on PRL telescopes for on-sky characterization and science observations. I will also talk about the current status of the data reduction pipeline being developed for ProtoPol.

Most optical spectropolarimeters built to date operate as long-slit or point-source instruments; they are inefficient for observations of extended objects such as galaxies and nebulae. 2D spectropolarimetry technique development is a major challenge in astronomical instrumentation. At the South African Astronomical Observatory (SAAO) FiberLab, we are developing a spectropolarimetry capable Integral Field front-end called FiberPol(-6D) for the existing SpUpNIC spectrograph on the SAAO 1.9 m telescope. SpUpNIC is a general purpose 2 arc-minute long-slit spectrograph with a grating suite covering the wavelength range from 350 to 1000 nm. FiberPol generates 6D observational data: x-y spatial dimensions, wavelength, and the three linear Stokes parameters I, q and u. Using a rotating half-wave plate and a Wollaston prism, FiberPol executes two-channel polarimetry, and each channel is fed to an array of 14 fibers, corresponding to a field of view of 10×20 arcseconds^2 sampled with 2.9 arcsecond diameter fiber cores. FiberPol aims to achieve a polarimetric accuracy of 0.1 % per spectral resolution bin. Further, it can also function as a non-polarimetric integral-field unit. The primary science goals include study of ISM of nearby galaxies to test the models of dust grain alignment and its dependence with the ambient magnetic field. The instrument design has been completed and it is currently being assembled and characterized in the lab. It is scheduled for on-sky commissioning in the second half of 2024. In this talk, I will present the scientific and technical goals of FiberPol, its overall design and initial results from the lab assembly and testing. FiberPol is a low cost technology demonstrator for 10m SALT and other large telescopes such as the 30m class telescopes. It can be modified and replicated for use on any existing spectrograph, especially on bigger telescopes.

Blazars are a special subclass of active galactic nuclei, with relativistic jets pointing close to observers’ line of sight, making them the most luminous and rapidly variable extra-galactic sources in the universe. Their observed emissions are highly Doppler boosted and observable across the entire accessible electromagnetic spectrum (from radio to gamma-rays), with diverse variability timescales ranging from minutes to years. The observed emissions imply extreme physical conditions that are beyond replication by any current or future terrestrial laboratory. Almost every aspect, from jet formation, collimation to gamma-ray production in the jets, is poorly understood. However, over the past decade, the availability of long-term, high-cadence data in the multi-wavelength regime (i.e., optical, X-ray, and gamma-ray) has been helpful in addressing some aspects of these issues through study of i) multi-wavelength flux and spectral variability on diverse time scales, ii) physical origin of quasi periodic oscillations (QPOs) observed in the light curves, iii) multi-wavelength flux distribution of Blazars. In this talk, we will discuss our recent interesting results on the above topics related to Blazar emission properties.

To date, over 5500 exoplanets have been observed, with the radial velocity method, utilizing Doppler shifts in light, proving its effectiveness. Advancements in spectrograph technology now enable us to detect and analyze subtle Doppler signals, potentially leading to the discovery of Earth-like exoplanets. However, challenges remain, particularly in wavelength calibration techniques. To address this, we propose a new approach utilizing Fabry-Perot etalons (FPE) in conjunction with PRL's cutting-edge spectrograph, PARAS-2. In this presentation, we will discuss recent advancements, including calculations regarding pressure and temperature stability, and showcase the design of the optomechanical assembly for the FPE.

The sub-Saturn classification of exoplanets refers to planets larger than Neptune but smaller than Saturn, typically falling within the range of 4-8 Earth radii. Sub-Saturns are considered failed gas giants with equally massive cores but significantly smaller total masses, having accreted envelopes that are much less than their cores. The absence of these planets in our solar system highlights the variety of possible planetary systems, and studying them around other stars provides valuable insights into this diversity. In this talk, I will discuss our recent discovery of a sub-Saturn TOI-6651b using PARAS-2 spectroscopic observations. TOI-6651b is transiting around a sub-giant, metal-rich G-type star in a ~5.06 day orbit. Joint fitting of the radial velocities from PARAS-2 and transit photometric data from TESS revealed planetary mass of ~59.4 Earth masses and a radius of ~5.30 Earth radii. TOI-6651b has a bulk density of ~2.18 g cm-³, positioning it among the select few known dense sub-Saturns and notably the densest among those detected with TESS. We find that a considerable portion ~85% of the planet's mass consists of dense materials such as rock/iron in the core, while the remaining mass comprises a low-density envelope of H/He. The existence of TOI-6651b challenges conventional planet formation theories and could be a result of merging events or significant atmospheric mass loss through tidal heating.

Several observational studies have shown that filaments are active sites of star-formation which makes them ideal laboratories to study the physical processes involved. However, star-formation remains a highly complex process, which is driven by an interplay between gravity, turbulence, magnetic fields, and stellar feedback. Among these, the exact role of magnetic fields in the process of star-formation and its interplay with other factors is the least understood. In this talk I will try to address two main questions: What role do magnetic fields play in the star formation process in filaments? How does stellar feedback affects the morphology of magnetic fields in filaments? Subsequently, I will present findings from our ongoing research on the factors responsible for driving the star-formation in the G47 filamentary cloud.

The advancement in X-ray astronomy is directly linked to the high-sensitivity observations primarily provided by X-ray telescopes. The fundamental parameters of X-ray telescopes, such as effective area, angular resolution, field of view, and energy response, define observational sensitivity. Significant improvement has been achieved in these parameters over the past few decades. However, further enhancement from a basic design perspective is constrained by the fact that X-ray reflection occurs only at grazing incident angles. This limitation leaves only the option for further improvement by reducing the geometrical uncertainty associated with X-ray mirrors. In this talk, I will discuss the role of X-ray telescopes in X-ray astronomy, their working principles, the possibility of improvement through design, various fabrication methods, metrology, along with their limitations.

Hub-Filament Systems (HFSs) are complex, web-like structures of filaments within molecular clouds and are widely known as nurseries for massive stars. While there is evidence of mass transfer from the molecular clouds to the hub through filaments, the exact driving factors of this process remain poorly understood. In this talk, I will review the current understanding of HFSs and present the findings from our ongoing work on the Galactic 'Snake' IRDC G11.11-0.12, which is known to host multiple HFSs. I will conclude by discussing how HFSs act as efficient material collection systems, ultimately favouring the formation of star clusters, including massive stars.

The transfer of mass between the two stellar components via an accretion disc, a characteristic of cataclysmic variables (CVs), gives rise to various intriguing astrophysical phenomena such as nova, dwarf nova, etc. It appears that the rate at which this transfer of mass takes place plays a significant role in the dwarf nova cycle and the behaviour of cataclysmics in general. Depending on it, a CV may show characteristics of a dwarf nova with semi-regular outbursts or a novalike variable. The canonical evolution model of cataclysmics suggests that different mechanisms are responsible for driving the mass transfer above and below the period gap (2 hr ≲ Porb ≲ 3 hr). However, the reduction and enhancement in the mass transfer rate (e.g. novalikes) and the underlying causes are still not understood well. In this talk, I will discuss the response of a cataclysmic system to different mass transfer rates. I will also present the calculation of mass transfer rate for the long period dwarf nova system V1948 Cyg and discuss how the results accord with the disc instability model.

Daksha is a proposed High Energy transients mission that will have higher sensitivity than any other mission in the world. Daksha will comprise of two satellites covering the entire sky from 1 keV to > 1 MeV. The primary objectives of the mission are to discover and characterize electromagnetic counterparts to gravitational wave sources; and to study Gamma Ray Bursts (GRBs). With its broadband spectral response, high sensitivity, and continuous all-sky coverage, it will discover fainter and rarer sources than any other existing or proposed mission. Daksha can make key strides in GRB research with polarization studies, prompt soft spectroscopy, and fine time-resolved spectral studies. In addition, Daksha is a versatile all-sky monitor that can address a wide variety of science cases. Daksha will provide continuous monitoring of X-ray pulsars. It will detect magnetar outbursts and high energy counterparts to Fast Radio Bursts. Using Earth occultation to measure source fluxes, the two satellites together will obtain daily flux measurements of bright hard X-ray sources including active galactic nuclei, X-ray binaries, and slow transients like Novae. Correlation studies between the two satellites can be used to probe primordial black holes through lensing. Daksha will have a set of detectors continuously pointing towards the Sun, providing excellent hard X-ray monitoring data. Closer to home, the high sensitivity and time resolution of Daksha can be leveraged for the characterization of Terrestrial Gamma-ray Flashes. In this talk, I will discuss the scientific impact of Daksha in all these areas

Massive star-forming regions (MSFRs) are commonly associated with hub-filament systems (HFSs) and sites of cloud-cloud collision (CCC). Recent observational studies of some MSFRs suggest a possible connection between CCC and the formation of HFSs. To understand this connection, we analyzed the magneto-hydrodynamic simulation data from Inoue et al. (2018). This simulation involves the collision of a spherical molecular cloud with a plane-parallel sea of dense molecular gas at a relative velocity of about 10 km/s. Following the collision, turbulent and non-uniform cloud undergoes shock compression, rapidly developing filamentary structures within the compressed layer. We found that CCC can lead to the formation of HFSs, which is a combined effect of turbulence, shock compression, magnetic fields, and gravity. The collision between the cloud components shapes the filaments into a cone and drives inward flows among them. These inward flows merge at the vertex of the cone, rapidly accumulating high-density gas, which can lead to the formation of massive star(s). The gas distribution in the position-velocity and position-position spaces highlights the challenges in detecting two cloud components and confirming their complementary distribution if the colliding clouds have a large size difference. However, such CCC events can be confirmed by the position-velocity diagrams presenting gas flow toward the vertex of the cone, which hosts gravitationally collapsing high-density objects, and by the magnetic field morphology curved toward the direction of collision. In this talk, I will present these initial results.

Education and its contribution to science, technology and innovation are the key points to combat poverty in the long term. Education is also a key point to empower girls and women, which is fundamental to achieve the United Nations Sustainable Development Goals (SDGs). Astronomy is a powerful tool to promote education and science but, in addition, it is also one of the leading sciences to bring strong technological developments and innovation. Africa has an amazing potential due to its natural and human resources for scientific research in astronomy. The situation of astronomy and space science in Africa has changed significantly in recent years, becoming emerging fields across the continent, and never before has it been as possible to use astronomy for development as it is today. This talk will first summarize the current status of astronomy developments in Africa. Secondly, using as an example different activities carried out for the development of education, science and technology in Ethiopia, East Africa and across the continent, it will show how through these we can fight poverty in the long term and increase in the future our chances of achieving the UN Sustainable Development Goals (SDGs) for the benefit of our whole society.