The similarity of the interstellar comet 2I/Borisov to solar system comets from high resolution optical spectroscopy

Abstract

2I/Borisov - hereafter 2I - is the first visibly active interstellar comet observed in the solar system, allowing us for the first time to sample the composition of a building block from another system. We report on the monitoring of 2I with UVES, the high resolution optical spectrograph of the ESO Very Large Telescope at Paranal, during four months from November 15, 2019 to March 16, 2020. Our goal is to characterize the activity and composition of 2I with respect to solar system comets. We collected high resolution spectra at 12 different epochs from 2.1 au pre-perihelion to 2.6 au post perihelion. On December 24 and 26, 2019, close to perihelion, we detected several OH lines of the 309 nm (0-0) band and derived a water production rate of $2.2\pm 0.2\times 10^{26}$ molecules/s. The three [OI] forbidden oxygen lines were detected at different epochs and we derive a green-to-red doublet intensity ratio (G/R) of $0.31\pm 0.05$ close to perihelion. NH${}_2$ ortho and para lines from various bands were measured and allowed us to derive an ortho-to-para ratio (OPR) of $3.21\pm 0.15$, corresponding to an OPR and spin temperature of ammonia of $1.11\pm 0.08$ and $31_{-5}^{+10}$ K, respectively. These values are consistent with the values usually measured for solar system comets. Emission lines of the radicals NH (336 nm), CN (388 nm), CH (431 nm), and C${}_2$ (517 nm) were also detected. Several FeI and NiI lines were identified and their intensities were measured to provide a ratio of log (NiI/FeI) = $0.21\pm 0.18$ in agreement with the value recently found in solar system comets. Our high spectral resolution observations of 2I/Borisov and the associated measurements of the NH${}_2$ OPR and the Ni/Fe abundance ratio are remarkably similar to solar system comets. Only the G/R ratio is unusually high but consistent with the high abundance ratio of CO/H${}_2$O found by other investigators.

Accepted for publication in A&A

References in corpus (16)

• The carbon monoxide-rich interstellar comet 2I/Borisov
• Unusually High CO Abundance of the First Active Interstellar Comet
• 2I/Borisov: A C${}_2$ depleted interstellar comet
• Detection of CN gas in Interstellar Object 2I/Borisov
• Coupled Chemistry-Emission Model for Atomic Oxygen Green and Red-doublet Emissions in Comet C/1996 B2 Hyakutake
• Detection of a Water Tracer in Interstellar Comet 2I/Borisov
• The effects of different Type Ia SN yields on Milky Way chemical evolution
• High resolution optical spectroscopy of the ${\mathrm{N}}_2$-rich comet C/2016 R2 (PanSTARRS)
• Detection of Diatomic Carbon in 2I/Borisov
• Carbon Chain Depletion of 2I/Borisov
• Compact pebbles and the evolution of volatiles in the interstellar comet 2I/Borisov
• Gaseous atomic nickel in the coma of interstellar comet 2I/Borisov
• Forbidden oxygen lines at various nucleocentric distances in comets
• Activity of the first interstellar comet 2I/Borisov around perihelion: Results from Indian observatories
• High-resolution optical spectroscopic observations of comet 21P/Giacobini-Zinner in Its 2018 apparition
• Comet 66P/du Toit: not a near Earth main belt comet

Cited by in corpus (11)

• Pre-perihelion evolution of the NiI/FeI abundance ratio in the coma of the interstellar comet 3I/ATLAS. From extreme to normal
• Very Large Telescope Observations of Interstellar Comet 3I/ATLAS. II. From Quiescence to Glow: Dramatic Rise of Ni i Emission and Incipient CN Outgassing at Large Heliocentric Distances*
• FeI and NiI in cometary atmospheres. Connections between the NiI/FeI abundance ratio and chemical characteristics of Jupiter-family and Oort-cloud comets
• Capture of interstellar objects II: by the Solar system
• Pre-perihelion Monitoring of Interstellar Comet 2I/Borisov
• Perihelion observations of interstellar comet 3I/ATLAS with the IRAM 30-m telescope
• Cometary science with CUBES
• Pre-perihelion Volatile Evolution of Interstellar Comet 3I/ATLAS Indicating Significant Contribution from Extended Source in the Coma
• Optical spectroscopy of comets using Hanle Echelle Spectrograph (HESP)
• Implications of evaporative cooling by H${}_2$ for 1I/`Oumuamua
• Ion abundances in the plasma tail of 3I/ATLAS show that it is N2-rich