Refereed journal articles
Activity of the first interstellar comet 2I/Borisov around perihelion: Results from Indian observatories
arXiv: 2101.02752
Abstract:
Comet 2I/Borisov is the first true interstellar comet discovered. Here, we present results from observational programs at two Indian observatories, 2 m Himalayan Chandra Telescope at the Indian Astronomical Observatory, Hanle (HCT) and 1.2 m telescope at the Mount Abu Infrared Observatory (MIRO). Two epochs of imaging and spectroscopy were carried out at the HCT and three epochs of imaging at MIRO. We found CN to be the dominant molecular emission on both epochs, 2019 November 30 and December 22, at distances of rH = 2.013 and 2.031 au, respectively. The comet was inferred to be relatively depleted in Carbon bearing molecules on the basis of low C2 and C3 abundances. We find the production rate ratio, Q(C2)/Q(CN) = 0.54 ± 0.18, pre-perihelion and Q(C2)/Q(CN) = 0.34 ± 0.12 post-perihelion. This classifies the comet as being moderately depleted in carbon chain molecules. Using the results from spectroscopic observations, we believe the comet to have a chemically heterogeneous surface having variation in abundance of carbon chain molecules. From imaging observations, we infer a dust-to-gas ratio similar to carbon chain depleted comets of the Solar system. We also compute the nucleus size to be in the range 0.18 km ≤ r ≤ 3.1 km. Our observations show that 2I/Borisov’s behaviour is analogous to that of the Solar system comets.
Optical observations and dust modelling of comet 156P/Russell-LINEAR
arXiv: 2101.02752
DOI: 10.1016/j.icarus.2022.115042
Abstract:
Comet 156P/Russell-LINEAR is a short period Jupiter family comet with an orbital period of 6.44 years. The results from spectroscopic, photometric, polarimetric observations and dust modelling studies are presented here. From the spectroscopic study, strong emissions from CN, C2 and C3 can be observed during both the epochs of our observations. The Q(C2)/Q(CN) ratio classifies the comet as a typical comet. The imaging data reveals the presence of jets. The dust emission from the comet is observed to have a non-steady state outflow due to the presence of these strong jets which subside in later epochs, resulting in a steady state outflow. Polarimetric study at two different phase angles reveals the degree of polarization to be comparable to Jupiter family comets at similar phase angles. Localized variations in polarization values are observed in the coma. The dust modelling studies suggest the presence of high amount of silicate/low absorbing material and indicate the coma to be dominated by higher amount of large size grains with low porosity having power law size distribution index = 2.4. The observed activity and dust properties points to a similarity to another Jupiter family comet, 67P/Churyumov–Gerasimenko.
Unique regolith characteristics of the lunar swirl Reiner Gamma as revealed by imaging polarimetry at large phase angles
DOI: 10.1051/0004-6361/202245356
Abstract:
Lunar swirls are high-albedo irregular markings that are generally associated with prominent magnetic anomalies. The formation of swirls is still unknown. Near-infrared spacecraft-based imaging suggests reduced space weathering at the locations of swirls. However, the reduced space weathering alone cannot explain the observed spectral properties.
We provide detailed physical characteristics of the regolith at the Reiner Gamma swirl. For the first time, systematic telescopic observations in a range of phase angles are used to derive the surface roughness, opposition effect strength, and grain size distribution at a spatial resolution of 1 km.
Imaging polarimetric observations of Reiner Gamma were obtained at the Mount Abu IR Observatory between January and March, 2021. These observations were collected with the two narrow-band continuum filters, GC (green) and RC (red), in a range of phase angles. The georeferenced polarimetric images were used to derive the single-scattering albedo, photometric roughness, and amplitude of the opposition effect by adopting the Hapke reflectance model. We further computed median regolith grain size maps of Reiner Gamma using the derived photometric roughness, albedo, and degree of polarization.
A comparison of the polarization properties of Reiner Gamma swirl with the craters Kepler and Aristarchus suggests grain size variations within the swirl structure. The Hapke modeling of the Reiner Gamma swirl suggests significant changes in the opposition effect strength at the central oval, but only marginal differences in surface roughness from its surroundings. Within the swirl, the median grain size varies significantly in comparison to the background mare grain size of around 45 µm.
Conclusions. Our results confirm the occurrence of surface alteration processes that might have disrupted the regolith microstructure in the Reiner Gamma swirl. These findings are consistent with an external mechanism of swirl formation, by considering interaction between the regolith and cometary gas. Subsequent to its formation, the swirl structure was preserved due to shielding by crustal magnetic field.
Long-term spectroscopic monitoring of comet 46P/Wirtanen
arXiv: 2401.03869
DOI: 10.1007/s12036-024-09996-6
Abstract:
Jupiter family comets, having an orbital period <20 years, allow us to observe their activity and analyze the homogeneity in their coma composition over multiple apparitions. Comet 46P/Wirtanen, with its exceptionally close approach to Earth during its 2018 apparition, offered the possibility for long-term spectroscopic observations. We used a 1.2 m telescope equipped with a low-resolution spectrograph to monitor the comet’s activity and compute the relative abundances in the coma as a function of heliocentric distance. We report the production rates of four molecules CN, C2, C3 and NH2 and Afρ parameter, a proxy to the dust production, before and after perihelion. We found that 46P has a typical coma composition with almost constant abundance ratios with respect to CN across the epochs of observation. Comparing the coma composition of comet 46P during the current and previous apparitions, we conclude the comet has a highly homogeneous chemical composition in the nucleus with an enhancement in ammonia abundance compared to the average abundance in comets.
Optical spectroscopy of comets using Hanle Echelle Spectrograph (HESP)
arXiv: 2403.01595
Abstract:
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
Multi-purpose InSTRument for Astronomy at Low-resolution: MISTRAL@OHP
arXiv: 2404.03705
DOI: 10.1051/0004-6361/202449254
Abstract:
MISTRAL is the new Faint Object Spectroscopic Camera mounted at the folded Cassegrain focus of the 1.93m telescope of Haute-Provence Observatory. We describe the design and components of the instrument and give some details about its operation. We emphasise in particular the various observing modes and the performances of the detector. A short description is also given about the working environment. Various types of objects, including stars, nebulae, comets, novae, galaxies have been observed during various test phases to evaluate the performances of the instrument. The instrument covers the range of 4000 to 8000A with the blue setting, or from 6000 to 10000A with the red setting, at an average spectral resolution of 700. Its peak efficiency is about 22% at 6000A. In spectroscopy, a limiting magnitude of 19.5 can be achieved for a point source in one hour with a signal to noise of 3 in the continuum (and better if emission lines are present). In imaging mode, limiting magnitudes of 20-21 can be obtained in 10-20mn (with average seing conditions of 2.5 arcsec at OHP). The instrument is very users-friendly and can be put into operations in less than 15mn (rapid change-over from the other instrument in use) if required by the science (like for Gamma-Rays Bursts). Some first scientific results are described for various types of objects, and in particular for the follow-up of GRBs. While some further improvements are still under way, in particular to ease the switch from blue to red setting and add more grisms or filters, MISTRAL is ready for the follow-up of transients and other variable objects, in the soon-to-come era of e.g. the SVOM satellite and of the Rubin telescope.
Refereed conference proceedings
1) Solar system studies with the Indo-Belgian telescopes.
Conference: Belgo-Indian Network for Astronomy and Astrophysics (BINA).
JOURNAL: Bulletin of Liege Royal Society of Sciences.
YEAR: 2019
2) EMPOL: an EMCCD based optical imaging polarimeter.
DOI: 10.1117/12.2560949
Conference: Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, 114479E
YEAR: 2020
3) Regolith Characteristics of the Reiner Gamma Swirl as Revealed by Polarimetric Observations.
DOI: www.hou.usra.edu/meetings/lpsc2021/pdf/2430.pdf
Conference: 52nd Lunar and Planetary Science Conference
YEAR: 2021
4) Regolith properties of the lunar swirl Reiner Gamma inferred from phase ratio and polarimetric imaging.
DOI: NASA ADS
Conference: 44th COSPAR Scientific Assembly
YEAR: 2022
5) Revealing the ionic emissions in the comet C/2020 F3 (NEOWISE).
Link: https://www.hou.usra.edu/meetings/acm2023/pdf/2501.pdf
Conference: Asteroids, Comets, Meteors Conference
YEAR: 2023
6) The Carbon-Chain depletion of recently observed Jupiter family comets from photometry and spectroscopy.
Link: https://www.hou.usra.edu/meetings/acm2023/pdf/2461.pdf
Conference: Asteroids, Comets, Meteors Conference
YEAR: 2023
7) Optical spectroscopy of comets.
Conference: Belgo-Indian Network for Astronomy and Astrophysics (BINA).
JOURNAL: Bulletin of Liege Royal Society of Sciences.
YEAR: 2023
8) Spectropolarimetric Properties of the Lunar Swirl Reiner Gamma and Western Oceanus Procellarum.
DOI: https://www.hou.usra.edu/meetings/lpsc2023/pdf/1609.pdf
Conference: 54th Lunar and Planetary Science Conference
YEAR: 2023
9) MISTRAL observations of the C/2022 E3 (ZTF) comet by the Aix-Marseille M2 students: First science results.
DOI: http://sf2a.eu/proceedings/2023/2023sf2a.conf.511A.pdf
JOURNAL: SF2A-2023, Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics.
Conference: Annual meeting of the French Society of Astronomy and Astrophysics
YEAR: 2023
10) Pre-perihelion TRAPPIST monitoring of the outbursting Halley- type comet 12P/Pons-Brooks
DOI: https://doi.org/10.5194/epsc2024-951
Conference: Europlanet Science Congress
YEAR: 2024
11) Long-term TRAPPIST monitoring of a few Long Period and Dynamically New Comets
DOI: https://doi.org/10.5194/epsc2024-1139
Conference: Europlanet Science Congress
YEAR: 2024
Atronomers Telegram
1) CN, C2, C3 production rates of Comet C/2020 F3 (NEOWISE) as observed from Himalayan Chandra Telescope, Hanle.
LINK: ATel#13897
YEAR: 2020
2) Molecular gas production rates of Comet C/2023 A3 (Tsuchinshan - ATLAS)
LINK: ATel#16637
YEAR: 2024