Water Production Rates And Activity Of Interstellar Comet 2I/Borisov


Co-added Swift/UVOT observations of 2I/Borisov (Left: UVW1; Right: V). Positions of the comet nucleus are indicated by white x-marks. White circles indicate photometric apertures used to measure water production rate and all have radii of 100 000 km, with lengths of the scale indicators equaling to these radii. Black circles indicate apertures used to measure A(θ)f ρ, with radii of 10 000 km for the last three visits and a larger radius of 12 000 km for the September visit to ensure the aperture exceeded UVOT’s PSF. All panels have the same physical scale (170×247 arcsec), and have been individually stretched linearly for optimal presentation, with north up, east to the left.

We observed the interstellar comet 2I/Borisov using the Neil Gehrels-Swift Observatory's Ultraviolet/Optical Telescope. We obtained images of the OH gas and dust surrounding the nucleus at four epochs spaced before and just after perihelion (-2.56 AU to 2.03 AU).

Water production rates increased steadily before perihelion from (7.0±1.5)×1026 molecules s−1 on Nov. 1, 2019 to (10.7±1.2)×1026 molecules s−1 on Dec. 1. This rate of increase in water production rate is slower than that of most Jupiter-family comets and quicker than most dynamically new comets. After perihelion, the water production rate decreased rapidly to (4.9±0.9)×1026 molecules s−1 on Dec. 21. Our sublimation model constrains the minimum radius of the nucleus to 0.37 km, and indicates an active fraction of at least 55% of the surface. A(0)fρ calculations show variation between 90 and 106 cm with a slight trend peaking before the perihelion, lower than previous and concurrent published values. The observations confirm that 2I/Borisov is carbon-chain depleted and enriched in NH2 relative to water.

Zexi Xing, Dennis Bodewits, John Noonan, Michele T. Bannister
(Submitted on 14 Jan 2020)
Comments: 11 pages, 3 figures, 2 tables, submitted to ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2001.04865 [astro-ph.EP] (or arXiv:2001.04865v1 [astro-ph.EP] for this version)
Submission history
From: Zexi Xing
[v1] Tue, 14 Jan 2020 16:01:33 UTC (1,574 KB)
https://arxiv.org/abs/2001.04865
Astrobiology, Astrochemistry

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