भारतीय खगोलभौतिकी संस्थान
Indian Institute of Astrophysics
Exploring the Universe since 1786
An Autonomous Institute under the
Department of Science & Technology
Government of India
Research Highlights
RESEARCH HIGHLIGHTS | IIA
Demography of stellar radio population within 500 pc: a VLASS-gaia DR3 study
ARUN SURYA | Dec 01, 2024
In this work, we have carried out a systematic analysis of the Very Large Array Sky Survey (VLASS) quick look catalogs together with Gaia DR3 to identify the optical counterparts of 3 GHz radio emitters within 500 pc to obtain a homogeneous statistical sample of stellar radio sources. We have identified distinct populations of 3 GHz emitters across the Gaia DR3 color–magnitude diagram. We also present candidate sources (transient, highly variable, or background artifacts) that can be confirmed by follow-up observations. A majority of the detected sources constitute main-sequence G-, K-, and M-type stars, including ultracool dwarfs. Pinning down the origin of radio emission from these populations can help us gain further insights into the origin of stellar and planetary magnetic fields. By analyzing the variation of brightness temperature of the sources with their spectral type, we have tentatively associated possible emission mechanisms with different object types. We inspected the correlation between quiescent radio and X-ray emission for our sample, which can provide crucial insights into the current understanding of the Gudel–Benz relationship, which is essential for modeling steady radio emission and coronal heating. This VLASS-Gaia DR3 analysis acts as a pilot study for follow-up observations at multiple wavelengths to better understand stellar structure, model flaring activities, and detect radio emission caused by star–planet interactions.
RESEARCH HIGHLIGHTS | IIA
On the properties of X-Ray corona in Seyfert 1 galaxies
STALIN, C. S | Nov 20, 2024
We carried out a uniform and systematic analysis of a sample of 112 nearby bright Seyfert 1 type active galactic nuclei, the observations of which were carried out by the Nuclear Spectroscopic Telescope Array between 2013 August and 2022 May. The main goal of this analysis is to investigate the nature of the X-ray corona in Seyfert 1 galaxies. By fitting a physical model to the NuSTAR spectra, we could constrain the high-energy cutoff (Ecut) for 73 sources in our sample. To estimate the temperature of the corona (kTe) in our sample of 112 sources, we used the Comptonization model to fit their spectra. We could constrain kTe in 42 sources. We found a strong positive correlation between Ecut and kTe, with most of the sources lying above the empirical approximation of Ecut = 2−3 kTe. We investigated for possible correlations between various properties of the corona obtained from physical model fits to the observed spectra and between various coronal parameters and physical properties of the sources such as Eddington ratio and black hole mass. We found (a) a strong correlation between Ecut and the photon index and (b) a significant negative correlation between kTe and the optical depth. From detailed statistical analysis of the correlation of coronal parameters with the Eddington ratio and black hole mass, we found no significant correlation. The correlations observed in this study indicate that an optically thin corona is needed to sustain a hotter corona with a steeper spectrum
RESEARCH HIGHLIGHTS | IIA
Dependence of spicule properties on the magnetic field—Results from magnetohydrodynamics simulations
PIYALI CHATTERJEE | Sep 20, 2024
Solar spicules are plasma jets observed in the interface region between the visible solar surface and the corona. At any given time, there is a forest of spicules originating in the chromosphere of the Sun. While various models attempt to elucidate their origin and characteristics, here, we consider the one driven by the magnetoconvection undulations. The radiative magnetohydrodynamic (rMHD) equations are solved using PENCIL CODE with a spatial resolution of 16 km using various magnetic field strengths. The obtained rMHD simulation data are investigated to unveil the various trends in spicular properties as a function of the applied magnetic fields. The important outcome of this study is the finding of a consistent reduction in both the number density and the maximum height reached by spicules as magnetic field strength increases. We also use parabolic fitting on time–distance curves of spicules that are taller than the 75th percentile in the distribution, in order to find a relation between the deceleration of the spicule tip and the magnetic field strength. Our results offer insights into the response of solar spicules to magnetic field strength.
Press Releases
PRESS RELEASES | SCOPE
A new method to reliably estimate Helium abundance in the Sun
SCOPE | Apr 24, 2025
Since Helium does not produce any observable spectral lines from the visible surface, or the photosphere, of the Sun, its abundance has usually been estimated through indirect means. In a recent study, the abundance of Helium in our Sun has been estimated accurately using the Magnesium and Carbon features in the observed high-resolution spectrum of the Sun.
This is based on the paper titled "Helium Abundance of the Sun: A Spectroscopic Analysis", by Satyajeet Moharana, B. P. Hema, and Gajendra Pandey, 2024, Astrophysical Journal, 974, 2.
Press release by PIB published here.
Press release issued by DST here.
Download the paper from here.
PRESS RELEASES | SCOPE
Scientists Chart the Sun's Subsurface Weather Patterns Tied to Its 11-Year Activity Cycle
SCOPE | Apr 29, 2025
An international team of solar physicists has unveiled new insights into the dynamic "inner weather" of the Sun—plasma currents just beneath its surface that pulse in step with its 11-year sunspot cycle. In a study published on the 22nd of April 2025, in the The Astrophysical Journal Letters, researchers from the Indian Institute of Astrophysics (IIA), Stanford University (USA), and the National Solar Observatory (NSO, USA) have traced how these hidden flows shift over time, potentially reshaping our understanding of how the Sun's interior connects to its outer magnetic behavior, which has far-reaching influence on space weather and Earth.
This is based on the paper titled "Solar Cycle Variations in Meridional Flows and Rotational Shear within the Sun's Near-surface Shear Layer", by Anisha Sen, S. P. Rajaguru, Abhinav Govindan Iyer, Ruizhu Chen, Junwei Zhao, and Shukur Kholikov, 2025, Astrophysical Journal Letters, 984, 1.
Press release by PIB published here.
Press release issued by DST here.
Download the paper from here.
PRESS RELEASES | SCOPE
IIA Bengaluru scientists discover a new kind of Stellar Chemistry
SCOPE | Jun 19, 2025
Far away in the Ophiuchus Constellation, a peculiar star named A980, 25800 light years away, is rewriting what we know about stellar chemistry. Researchers have uncovered a cosmic twist -- this mysterious star that belongs to a rare class called Extreme Helium (EHe) stars, carries surprisingly high amount of germanium—a metallic element never before observed in this type of star.
This is based on the paper titled "Detection of Enhanced Germanium in a New Cool Extreme Helium Star A980: Insights and Implications", by Ajay Kumar Saini and Gajendra Pandey, 2025, The Astrophysical Journal, 979, 239.
Press release by PIB published here.
Press release issued by DST here.
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PhD Programme
IIA offers a vigorous programme of graduate studies that forms a vital component of research & training. The programme is overseen by the board of graduate studies. The Institute is also a major partner in the Joint Astronomy Programme (JAP), organized by the Indian Institute of Science.
Admissions
PhD applications may be submitted through the IIA PhD online applications portal in May. After the initial screening, shortlisted candidates will be interviewed in June. The final list of selected candidates will be announced in July, followed by the commencement of the programme in August. .
Research Fields
Solar Studies
Studies of the Sun and solar system have been the longest pursued discipline at IIA. Members of the group conduct theoretical, numerical modeling, and observational studies in solar physics.
Stars & Galaxies
Research interests of the group members range from exoplanets, star formation, stellar evolution, end states of stars, Interstellar medium, the milky way Galaxy, nearby galaxies, active galaxies and time domain astronomy.
Theory
Members of the theoretical Astrophysics group work on a broad range of topics such as black hole astrophysics, pulsars, exoplanets, astrophysical turbulence & magnetic fields, MHD, cosmology and early universe.
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