Please use this identifier to cite or link to this item: http://hdl.handle.net/2248/8487
Title: Optical spectroscopy of comets using Hanle Echelle Spectrograph (HESP)
Authors: Aravind, K
Venkataramani, Kumar
Ganesh, Shashikiran
Surya, Arun
Sivarani, T
Sahu, D. K
Unni, Athira
Bhardwaj, Anil
Keywords: Methods: observational
Techniques: spectroscopic
Comets: general
Issue Date: May-2024
Publisher: Oxford University Press on behalf of Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society, Vol. 530, No. 1, pp. 393–404
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/λ) = 30 000 and 60 000) spectra of several comets, including C/2015 V2 (Johnson), 46P/Wirtanen, 41P/Tuttle–Giacobini–Kresak, ´ 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.
Description: Open Access.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
URI: http://hdl.handle.net/2248/8487
ISSN: 0035-8711
Appears in Collections:IIAP Publications

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