Detection Of CN Gas In Interstellar Object 2I/Borisov

(a) Flux calibrated spectrum of 2I/Borisov through a 200 by 800 aperture centered on the comet. Also shown is a scaled Solar spectrum reddened to match the observed dust continuum. (b) Spectral region around the CN (0-0) emission band with the background dust continuum subtracted.

The detection of Interstellar Objects passing through the Solar system offers the promise of constraining the physical and chemical processes involved in planetary formation in other extrasolar systems.

While the effect of outgassing by 1I/2017 U1 ('Oumuamua) was dynamically observed, no direct detection of the ejected material was made. The discovery of the active interstellar comet 2I/Borisov means spectroscopic investigations of the sublimated ices is possible for this object.

We report the first detection of gas emitted by an interstellar comet via the near-UV emission of CN from 2I/Borisov at a heliocentric distance of r = 2.7 au on 2019 September 20. The production rate was found to be Q(CN) = (3.7±0.4)×1024 s−1, using a simple Haser model with an outflow velocity of 0.5 km s−1. No other emission was detected, with an upper limit to the production rate of C2 of 4×1024 s−1. The spectral reflectance slope of the dust coma over 3900 Å <λ<6000 Å\ is steeper than at longer wavelengths, as found for other comets. Broad band Rc photometry gave a dust production rate of Afρ=143±10 cm−1.

Modelling of the observed gas and dust production rates constrains the nuclear radius to 0.7−3.3 km assuming reasonable nuclear properties. Overall, we find the gas, dust and nuclear properties for the first active Interstellar Object are similar to normal Solar system comets.

Alan Fitzsimmons, Olivier Hainaut, Karen Meech, Emmanuel Jehin, Youssef Moulane, Cyrielle Opitom, Bin Yang, Jacqueline V. Keane, Jan T. Kleyna, Marco Micheli, Colin Snodgrass
(Submitted on 26 Sep 2019)

Comments: 10 pages, 4 figures, 1 table
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1909.12144 [astro-ph.EP] (or arXiv:1909.12144v1 [astro-ph.EP] for this version)
Submission history
From: Alan Fitzsimmons
[v1] Thu, 26 Sep 2019 14:27:23 UTC (236 KB)
Astrochemistry, Astrobiology

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