Advancing the Warm Calibration Unit for METIS on ELT: From Design Finalization to MAIT Phase
Abstract
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.
Broad-band study of the SMC pulsar RX J0032.9-7348 during its X-ray brightening in 2024
Abstract
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.
Census and Characterization of Hot and Variable Stars in Star Clusters
Abstract
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.
Characterizing AGN and dual AGN duty cycles in SMUGGLE isolated merger simulations
Abstract
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.
Observing Solar Flares with SUIT: A New Window into the Near-Ultraviolet Sun
Abstract
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.
Multi-mode study of exotic stellar populations in dense stellar systems
Abstract
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.
The Secret Lives of Galaxies: From Dusty Starbursts to Buried Black Holes
Abstract
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.
Atmospheric evaporation from exoplanets
Abstract
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.
Time-Dependent Modeling of Extreme Gamma-Ray Flares of Blazars
Abstract
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
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).
The African Network of Women in Astronomy (AfNWA) and SciGirls: Examples of social activism
Abstract
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) as electromagnetic (EM) counterparts of Gravitational Wave (GW) sources
Abstract
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.
Hot Jupiter Exoplanets: The Enigmatic Giants of Astrophysics
Abstract
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.
Fabry-Perot wavelength calibration system for precise radial velocity measurements
Abstract
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.
Solar Coronal Phenomena: Imaging X-ray Spectroscopy
Abstract
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 in the Milky Way as seen by GAIA
Abstract
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
Tracing Cosmic Origins: Unveiling Element Formation Through Stellar Archaeology
Abstract
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.
Probing accretion process and emission mechanism of X-ray pulsars in multi-wavelength
Abstract
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.
Probing the Cold Molecular Gas in Luminous Dusty Star-forming Galaxies at z~1-6
Abstract
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.