Title : Magnetic Accretion Signatures in High-Field Cataclysmic Variables

Abstract

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.

Title : Investigating the Impact of Hydrogen on Lunar Neutron Leakage Flux

Abstract

The Moon's lack of a magnetic field and atmosphere exposes its surface to ionizing radiation, including the solar wind, solar energetic particles (SEPs), and galactic cosmic rays (GCRs). High-energy GCRs interact with the lunar surface, generating fast neutrons through nuclear reactions. These fast neutrons are moderated by collisions with the nuclei in the lunar soil and can leak out, acting as messengers of the soil’s composition. Studying the neutron leakage spectrum can reveal important information about the abundance of near-surface hydrogen. In this seminar, I will discuss the production and moderation processes of neutrons within the lunar surface, followed by an explanation of how the leakage neutron flux depends on hydrogen and other elements.

Title : Verification of the Dynamically New Comets: Results from the N-body Simulation

Abstract

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.

Title : Advances in Direct Imaging of Exoplanets

Abstract

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.

Title : Origin of Soft excess in Mrk50

Abstract

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.

Title : Investigating the explosion and progenitor properties of Type II core-collapse supernovae

Abstract

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 the 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.

Title : Global Detection of Lunar Pyroclastic Deposits (LPDs)

Abstract

Lunar Pyroclastic Deposits (LPDs) are fine-grained, low-albedo, Fe-Ti-rich volcanic glass-dominated lithological units typically associated with thin crust and extensional tectonic regimes on the Moon. These deposits are providing key insight into thermal evolution and volatile inventory of the Moon. However, their remote detection remains challenging due to the spectral similarities between volcanic glasses and Fe-bearing common lunar minerals (e.g., Olivine, Pyroxene, etc.) in the visible to near-infrared (VIS-NIR) spectral range. In this seminar, I will present a novel approach developed for remote detection of LPDs by incorporating morphological understanding with the spectral analysis covering both the spectral parameters. I will present new global​ LPDs maps, based on the Moon Mineralogy Mapper (M3) data of two different optical periods. The results will be validated by comparing the global outcomes to already reported LPDs. The main outcome of this work is new​ detections. I will present a few case studies on new detections and validation to confirm their pyroclastic origin. I will also discuss the inferences and implications during this seminar.

Title : Delving into the Extremes of Neutron Stars: Insights from Thermonuclear X-ray Bursts

Abstract

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.

Title : The Role of Layered Minerals in the Origin of Life Insights from Planetary Analogue Terrestrial Geomaterials​

Abstract

How did life begin? Researchers believe that certain minerals, especially clays, played a big role in this process. These minerals can hold onto organic molecules, help chemical reactions happen, and create safe spaces for early life to form. Since they exist on Earth and other planets, they also help us search for signs of life beyond our planet. These layered minerals, abundant in terrestrial and extraterrestrial environments, serve as key indicators of fluid-rock interactions and potential biosignature preservation. This talk will explore how clays can serve as one of the potential planetary analogue terrestrial geomaterials that can enhance our understanding of life’s emergence. By employing comprehensive biogeochemical fingerprinting, this research will characterize clay minerals in terrestrial settings, assessing their capacity to preserve biosignatures. By studying layered minerals on Earth and extending these findings to available extraterrestrial samples, we can unveil the largely unexplored role of clay minerals in the origin of life, which is essential for planning future astrobiological missions.

Title : Towards a Unified Understanding of Accreting Compact Objects

Abstract

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.

Title : A Monte Carlo Approach to Temperature and Spectral Energy Distribution in Protoplanetary Disks

Abstract

A protoplanetary disk is a rotating circumstellar disk of dense gas and dust surrounding a young star. Understanding the structure and composition of these disks is essential for understanding the processes involved in planet formation. Over the years, various models have been developed to describe the chemical and hydrodynamic processes occurring within these disks. Here, we introduce a Monte Carlo Radiative Transfer (MCRT) model to characterize the temperature distribution and spectral energy throughout the disk and its surrounding envelope. MCRT method provides an efficient means of achieving radiative equilibrium without iteration in systems with temperature-independent opacity sources. Additionally, the computational time required for this method is comparable to that of pure scattering models. The MCRT approach tracks individual photon packets, allowing for precise identification of energy absorption sites and subsequent adjustments to local cell temperatures. To enforce radiative equilibrium, each absorbed packet is instantly re-emitted, with its frequency selected to correct the cell’s thermal spectrum. These re-emitted packets can undergo scattering, absorption, and re-emission processes until they escape, enabling the system’s temperature and spectral energy distribution (SED) to reach equilibrium. We present the initial results of the simulations for both spherical symmetry models and 2D axisymmetric density structures, comparing the findings with standard benchmark tests.

Title : FIELD-ANGLE OPTIMIZED DESIGN FOR WIDE-FIELD IMAGING X-RAY TELESCOPES

Abstract

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.

Title : Time domain photometric study of peculiar Blazars

Abstract

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).

Title : Habitat Selection by Early Humans in the Indian Subcontinent

Abstract

The dispersal of our species out of Africa is believed to have occurred in multiple phases from the middle to late Pleistocene. Earliest fossil evidences for this migration of Homo sapiens is documented around 200-100 kya. These dispersals are influenced by the climate shifts, which shaped their habitats during migration. According to the Southern Dispersal Hypothesis, the dispersal of Homo sapiens from Africa into South Asia (130–75 kya) coincided with periods of favorable monsoon-driven green corridors, which influenced migration pathways and habitat selection. In this seminar, we will explore hominin habitat selection patterns by reconstructing woody cover along these dispersal routes using pedogenic carbonates as a vegetation proxy, providing insights into the environments they might have encountered and adapted.