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
Helium Abundance of the Sun: A Spectroscopic Analysis
HEMA, B. P | Oct 20, 2024
Determining the He/H ratio in cool stars presents a fundamental astrophysical challenge. While this ratio is established for hot O and B stars, its extrapolation to cool stars remains uncertain due to the absence of helium lines in their observed spectra. We address this knowledge gap by focusing on the Sun as a representative cool star. We conduct spectroscopic analyses of the observed solar photospheric lines by utilizing a combination of MgH molecular lines and neutral Mg atomic lines including yet another combination of CH and C2 molecular lines with neutral C atomic lines. Our spectroscopic analyses were further exploited by adopting solar model atmospheres constructed for distinct He/H ratios to determine the solar photospheric helium abundance. The helium abundance is determined by enforcing the fact that for an adopted model atmosphere with an appropriate He/H ratio, the derived Mg abundance from the neutral Mg atomic lines and that from the MgH molecular lines must be the same. The same holds for the C abundance derived from neutral C atomic lines and that from CH lines of the CH molecular band and C2 lines from the C2 Swan band. The estimated He/H ratio for the Sun is discussed based on the one-dimensional local thermodynamic equilibrium model atmosphere. The helium abundance (He/H = - + 0.091 0.014 0.019) obtained for the Sun serves as a critical reference point to characterize the He/H ratio of cool stars across the range in their effective temperature.
RESEARCH HIGHLIGHTS | IIA
Optical spectroscopy of comets using Hanle Echelle Spectrograph (HESP)
ARUN SURYA | May 01, 2024
Observing the vibrational/rotational lines in a comet’s optical spectrum requires high-resolution spectroscopy, as they are otherwise seen as a blended feature. To achieve this, we have obtained medium and high-resolution (R (λ/Δλ) = 30 000 and 60 000) spectra of several comets, including C/2015 V2 (Johnson), 46P/Wirtanen, 41P/Tuttle–Giacobini–Kresák, and 38P/Stephan–Oterma, using the Hanle Echelle Spectrograph (HESP) mounted on the 2-m Himalayan Chandra Telescope (HCT) in India. The spectra effectively cover the wavelength range 3700–10 000 Å, allowing us to probe the various vibrational bands and band sequences to identify the rotational lines in the cometary molecular emission. We were also able to separate the cometary Oxygen lines from the telluric lines and analyse the green-to-red (G/R) forbidden oxygen [O i] ratios in a few comets. For comets C/2015 V2, 46P, and 41P, the computed G/R ratios, 0.04 ± 0.01, 0.04 ± 0.01, and 0.08 ± 0.02, respectively, point to H2O being a major source of Oxygen emissions. Notably, in the second fibre pointing at a location 1000 km away from the photocentre of comet 46P, the G/R ratio reduced by more than half the value observed in the first fibre, indicating the effects of quenching within the inner coma. We also measured the NH2 ortho-to-para ratio of comet 46P to be about 3.41 ± 0.05 and derived an ammonia ratio of 1.21 ± 0.03 corresponding to a spin temperature of ∼26 K. With these, we present the results of the study of four comets from different cometary reservoirs using medium and high-resolution optical spectroscopy, emphasizing the capabilities of the instrument for future cometary studies.
RESEARCH HIGHLIGHTS | IIA
Redshifts of candidate host galaxies of four fast X-ray transients using VLT/MUSE
DEEPAK EAPPACHEN | Sep 01, 2024
Fast X-ray transients (FXTs) are X-ray flares that last from minutes to hours. Multi-wavelength counterparts to these FXTs have proven hard to find. As a result, distance measurements are made through indirect methods such as a host galaxy identification. Of the three main models proposed for FXTs, that is, supernova shock breakout emission (SN SBO), binary neutron star (BNS) mergers, and tidal dirsuption events (TDEs) of an intermediate-mass black hole (IMBH) disrupting a white dwarf (WD), the SN SBO predicts a much lower maximum peak X-ray luminosity (LX,peak). If the distance to FXTs were to be obtained, it would be a powerful probe for investigating the nature of these FXTs. Aims. We aim to obtain distance measurements to four FXTs by identifying candidate host galaxies. Through a redshift measurement of the candidate host galaxies, we derive LX,peak and the projected offset between the candidate host galaxy and the FXT. Methods. We obtained Very Large Telescope (VLT)/Multi Unit Spectroscopic Explorer (MUSE) observations of a sample of FXTs. We report the redshift of between 13 and 22 galaxies per FXT. We used these redshifts to calculate the distance, LX,peak and the projected offsets between the FXT position and the position of the sources. Additionally, we computed the chance alignment probabilities for these sources with the FXT postitions. Results. We find LX,peak > 1044 erg s−1 when we assume that any of the sources with a redshift measurement is the true host galaxy of the corresponding FXT. For XRT 100831, we find a very faint galaxy (mR,AB = 26.5 ± 0.3, z ∼ 1.22, LX,peak ∼ 8 × 1045 erg s−1 if the FXT is at this distance) within the 1σ uncertainty region with a chance alignment probability of 0.04. For XRT 060207, we find a candidate host galaxy at z = 0.939 with a low chance alignment probability within the 1σ uncertainty region. However, we also report the detection of a late-type star within the 3σ uncertainty region with a similar chance alignment probability. For the remaining FXTs (XRT 030511 and XRT 070618), we find no sources within their 3σ uncertainty regions. The projected offsets between the galaxies and the FXT positions is >33 kpc at 1σ uncertainty. Therefore, if one of these candidate host galaxies turns out to be the true host galaxy, it would imply that the FXT progenitor originated from a system that received a significant kick velocity at formation. Conclusions. We rule out an SN SBO nature for all FXTs based on LX,peak and the projected offsets between the FXT position and the sources, assuming any of the candidate host galaxies with a redshift determination is the true host galaxy to the FXT. For XRT 100831, we conclude that the detected galaxy within the 1σ uncertainty position is likely to be the host galaxy of this FXT based on the chance alignment probability. From the available information, we are not able to determine whether XRT 060207 originated from the galaxy found within 1σ of the FXT position or was due to a flare from the late-type star detected within the 3σ uncertainty region. Based on LX,peak and the offsets within our sample, we are not able to distinguish between the BNS merger and the IMBD-WD TDE progenitor model. However, for the candidate host galaxies with an offset &30 kpc, we can conclude that the IMBH-WD TDE is unlikely due to the large offset.
Press Releases
PRESS RELEASES | SCOPE
Nascent galaxy discovered in formation at the end of the longest tidal tail of NGC 3785 galaxy
SCOPE | Jan 06, 2025
When astronomers from the Indian Institute of Astrophysics and their collaborators looked carefully at the galaxy NGC 3785, they found that not only does it have the longest tidal tail discovered so far, but that an ultra-diffuse galaxy is currently being formed at the end of this tidal tail as well.
This is based on the recently published paper titled "A Tale of NGC 3785: The formation of an ultra-diffuse galaxy at the end of the longest tidal tail", by Watts et al, 2024, Astronomy & Astrophysics, 691, L13.
Press release by PIB published here.
Press release issued by DST here.
Download the paper from here.
PRESS RELEASES | SCOPE
Iron lines in the X-ray detected from a binary black hole system that can help infer their properties
SCOPE | Jan 10, 2025
A study led by astronomers at the Indian Institute of Astrophysics has detected the Fe K spectral lines of ionized Iron atoms from the well-known binary Active Galactic Nucleus system 4C+37.11 using data from the Chandra Space Telescope. This is the first such detection from a binary black hole system, and they were able to conclude that this emission arises from both the accretion disk and the collisionally ionized plasma surrounding the pair of supermassive black holes in this object.
This is based on the recently published paper titled "Detection of the Fe K lines from the binary AGN in 4C+37.11", by Mondal et al, 2024, Astronomy & Astrophysics, 279, 7.
Press release by PIB published here.
Press release issued by DST here.
Download the paper from here.
PRESS RELEASES | SCOPE
International solar conference celebrates 125 years of solar physics research in India
SCOPE | Jan 24, 2025
More than 200 solar physicists from India and abroad have come together in Bengaluru this week for an international conference on “Sun, Space Weather, and Solar-Stellar Connections”. The conference is being organised by the Indian Institute of Astrophysics to commemorate the 125th anniversary of the Kodaikanal Solar Observatory and the birth of solar astrophysics in the country (conference webpage)
Download the PIB press release from 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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