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
The Hα Line as a Probe of Chromospheric Magnetic Fields
HARSH MATHUR | Jul 10, 2025
We explore the diagnostic potential of the Hα line for probing the chromospheric magnetic field using a realistic 3D radiative magnetohydrodynamic (rMHD) model. The Stokes profiles of the Hα line are synthesized through full 3D radiative transfer under the field-free approximation, alongside the Ca II 8542 Å and Fe I 6173 Å lines for comparison. The line-of-sight (LOS) magnetic fields are inferred using the weak-field approximation for the Hα and Ca II 8542 Å lines, while the Fe I 6173 Å line is analyzed through Milne-Eddington inversion techniques. The comparison between the inferred LOS magnetic field maps and the magnetic fields in the rMHD model revealed that the Hα line core primarily probes the chromospheric magnetic field at log 500 = −5.7, which corresponds to higher layers than the Ca II 8542 Å line core, which is most sensitive to conditions at log 500 = −5.1. On average, the Stokes V profiles of the Hα line core form 500 km higher than those of the Ca II 8542 Å line core. The Hα polarization signals persist after adding noise, and with noise at the level of 10−3 Ic, most simulated magnetic structures remain visible. These findings suggest that spectropolarimetric observations of the Hα line can provide complementary insights into the stratification of the magnetic field at higher altitudes, especially when recorded simultaneously with widely used chromospheric diagnostics such as the Ca II 8542 Å line.
RESEARCH HIGHLIGHTS | IIA
Detection of enhanced germanium in a new cool extreme helium star A980: insights and implications
PANDEY, G | Feb 01, 2025
A fine abundance analysis of a recently discovered hydrogen-deficient carbon (HdC) star, A980, is presented. Based on the observed high-resolution optical spectrum, we ascertain that A980 is a cool extreme helium (EHe) star and not an HdC star. Singly ionized germanium Ge II lines are identified in A980’s optical spectrum. These are the first-ever detections of germanium lines in an EHe star's observed spectrum and provide the first measurements of germanium abundance in an EHe star. The overabundance of germanium in A980’s atmosphere provides us with evidence for the synthesis of germanium in EHe stars. Among the known cool EHe stars, A980 exhibits a maximum enhancement of the s-process elements based on a significant number of transitions. The measured elemental abundances reveal signs of H-burning, He-burning, and specifically the nucleosyntheses of the key elements Ge, Sr, Y, Zr, and Ba. The nucleosyntheses of these key elements are discussed in light of asymptotic giant branch evolution and the expectation from the accretion of an He white dwarf by a C–O white dwarf or by a neutron star
RESEARCH HIGHLIGHTS | IIA
High-resolution spectroscopy of the variable hot post-AGB star LS 4331 (IRAS 17381‑1616)
PARTHASARATHY, M | Dec 01, 2024
An analysis of the high-resolution (R∼48000) optical spectrum of hot (B1Ibe) post-AGB star LS 4331 (IRAS 17381‑1616) is presented. The detailed identification of the observed absorption and emission features in the wavelength range 3700–9200 Å is carried out for the first time. The atmospheric parameters and chemical composition of the star are derived from the non-LTE analysis of absorption lines. We estimated Teff=20900±500 K, logg=2.57±0.08, Vr=-51.7±0.8 km s-1, ξt=24±4 km s-1 and vsini=30±5 km s-1. An abundance analysis for C, N, O, Mg, Al, S, and Si reveals that the N and O abundance is close to solar while metal underabundances relative to the solar value (i.e., [Mg/H]=-1.04 dex, [Al/H]=-1.20 dex, [Si/H]=-0.46 dex) are found. LS 4331 is a high galactic latitude metal-poor and carbon-deficient hot post-AGB star. The underabundance of carbon ([C/H]=-0.64 dex) is similar to that found in other hot post-AGB stars and indicates that the star's AGB phase of evolution was terminated before the third dredge-up. Plasma diagnostics are derived from the nebular emission lines. The presence of nebular emission lines in the spectrum of LS 4331 indicates that the photoionization of the circumstellar envelope has already started. The nebular parameters and expansion velocity of the nebula are derived. Using the Gaia DR3 distance, the absolute luminosity of the star is derived, and the star's position on the post-AGB evolutionary tracks suggests that its initial main sequence mass is about 1.2 M⊙. It is also reported that fast irregular brightness variations with an amplitude of up to 0.3 mag in the V band have been found in the star, typical of hot post-AGB objects.
Press Releases
PRESS RELEASES | SCOPE
IIA Celebrates 10 Years of Operation of the UltraViolet Imaging Telescope on board AstroSat
SCOPE | Dec 04, 2025
UIVT is the primary payload on board AstroSat, India’s first dedicated space observatory, launched on September, 28, 2015 by ISRO. AstroSat carries five payloads capable of observing simultaneously from the ultraviolet to soft X-rays and hard X-rays. UIVT was designed, assembled, tested, and delivered by IIA, from its campus in Hosakote. To commemorate this achievement and to plan for future space UV telescopes, IIA organised a one-day academic workshop on 4 December 2025, to mark 10 years since the opening of the doors of UVIT on 30 November 2015.
The UVIT image gallery can be seen here.
The DST press release is here.
The PIB press release is here.
PRESS RELEASES | SCOPE
When the inner wall fell: complex hydrocarbon molecules in a young stellar disk
SCOPE | Dec 26, 2025
Astronomers have unveiled an intriguing secret behind the dusty veil of a young star named T Chamaeleontis, quietly forming planets about 350 light-years from Earth when part of its circumstellar inner wall collapsed partially. This can help rewrite our understanding of how planetary systems evolve.
This study was published in The Astronomical Journal in a paper titled "When the Wall Fell: Study of Polycyclic Aromatic Hydrocarbons in T Chamaeleontis Using JWST", by R. Arun of IIA.
The paper can be downloaded from here
The PIB press release is here.
The DST press release is here.
PRESS RELEASES | SCOPE
Role of magnetic fields in the birth of a young star traced
SCOPE | Jan 14, 2026
A team led by IIA researchers have unveiled critical new observational evidence linking magnetic fields from the scale of molecular clouds down to the scale of dense star-forming cores using polarisation studies. This novel work sheds light on the morphology and strength of the magnetic fields across multiple spatial scales, and elucidates the competing roles of magnetic fields and gravity in the formation of proto-stars.
This study was published in the Monthly Notices of the Royal Astronomical Society in a paper titled "Magnetic fields on different spatial scales of the L328 cloud", by Shivani Gupta, Archana Soam, Janik Karoly, Chang Won Lee, and G. Maheswar.
The PIB press release is here.
The DST press release is here.
The paper can be downloaded from here.
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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.
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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. .
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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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150 YEARS OF VANDE MATARAM | 2025
150 years of 'Vande Mataram'
150 YEARS OF VANDE MATARAM | 2025
150 years of 'Vande Mataram'
150 YEARS OF VANDE MATARAM | 2025
150 years of 'Vande Mataram'
150 YEARS OF VANDE MATARAM | 2025
150 years of 'Vande Mataram'
150 YEARS OF VANDE MATARAM | 2025
150 years of 'Vande Mataram'
150 YEARS OF VANDE MATARAM | 2025
