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Detection of Diatomic Carbon in 2I/Borisov

Lin, Hsing Wen and Lee, Chien-Hsiu and Gerdes, D. W. and Adams, Fred C. and Becker, Juliette and Napier, Kevin and Markwardt, Larissa (2020) Detection of Diatomic Carbon in 2I/Borisov. Astrophysical Journal Letters, 889 (2). Art. No. L30. ISSN 2041-8213. doi:10.3847/2041-8213/ab6bd9.

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2I/Borisov is the first-ever observed interstellar comet (and the second detected interstellar object (ISO)). It was discovered on 2019 August 30 and has a heliocentric orbital eccentricity of ~3.35, corresponding to a hyperbolic orbit that is unbound to the Sun. Given that it is an ISO, it is of interest to compare its properties—such as composition and activity—with the comets in our solar system. This study reports low-resolution optical spectra of 2I/Borisov. The spectra were obtained by the MDM Observatory Hiltner 2.4 m telescope/Ohio State Multi-Object Spectrograph (on 2019 October 31.5 and November 4.5, UT). The wavelength coverage spanned from 3700 to 9200 Å. The dust continuum reflectance spectra of 2I/Borisov show that the spectral slope is steeper in the blue end of the spectrum (compared to the red). The spectra of 2I/Borisov clearly show CN emission at 3880 Å, as well as C2 emission at both 4750 and 5150 Å. Using a Haser model to covert the observed fluxes into estimates for the molecular production rates, we find Q(CN) = 2.4 ± 0.2 × 10²⁴ s⁻¹, and Q(C₂) = (5.5 ± 0.4) × 10²³ s⁻¹ at the heliocentric distance of 2.145 au. Our Q(CN) estimate is consistent with contemporaneous observations, and the Q(C₂) estimate is generally below the upper limits of previous studies. We derived the ratio Q(C₂)/Q(CN) = 0.2 ± 0.1, which indicates that 2I/Borisov is depleted in carbon-chain species, but is not empty. This feature is not rare for the comets in our solar system, especially in the class of Jupiter-family comets.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lin, Hsing Wen0000-0001-7737-6784
Lee, Chien-Hsiu0000-0003-1700-5740
Gerdes, D. W.0000-0001-6942-2736
Adams, Fred C.0000-0002-8167-1767
Becker, Juliette0000-0002-7733-4522
Napier, Kevin0000-0003-4827-5049
Alternate Title:Low Resolution Optical Spectra and Diatomic Carbon Detections of 2I/Borisov
Additional Information:© 2020 The American Astronomical Society. Received 2019 December 11; revised 2020 January 9; accepted 2020 January 14; published 2020 January 27. We thank Mario Mateo, Christopher Miller, Jules Halpern, and Eric Galayda for making the comet observations as scheduled. We thank Paul Martini and John Thorstensen for their advice on OSMOS configurations and observations. We thank Justin Rupert, Ryan Chornock, and the observational astronomy class of Ohio University for the training of MDM telescope operation. We thank Zhong-Yi Lin for comments on our data. This work is based on observations obtained at the MDM Observatory, operated by Dartmouth College, Columbia University, Ohio State University, Ohio University, and the University of Michigan. This material is based upon work supported by the National Aeronautics and Space Administration under grant No. NNX17AF21G issued through the SSO Planetary Astronomy Program and by NSF grant AST-1515015. Facility: MDM:Hiltner (OSMOS). - Software: Scipy (Virtanen et al. 2019), Astropy (Astropy Collaboration et al. 2013, 2018), Matplotlib (Hunter 2007), Jupyter, sbpy (Mommert et al. 2019).
Funding AgencyGrant Number
Subject Keywords:Comets
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Comets (280)
Record Number:CaltechAUTHORS:20200127-133104038
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Official Citation:Hsing Wen Lin et al 2020 ApJL 889 L30
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100947
Deposited By: Tony Diaz
Deposited On:28 Jan 2020 18:48
Last Modified:16 Nov 2021 17:58

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