Comets and Asteroids

Comets 12CO+ and 13CO+ Fluorescence Models For Measuring The 12C/13C Isotopic Ratio In CO+

By Keith Cowing
Status Report
November 13, 2023
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Comets 12CO+ and 13CO+ Fluorescence Models For Measuring The 12C/13C Isotopic Ratio In CO+
12CO+ and 13CO+ theoretical spectra superimposed to the observational data obtained on comet C/2016 R2. The relative intensity of 13CO+ emission lines are based on the 12CO+ fit of the emission lines. They do not respect the intensities observed in this comet, the purpose of this plot being only to show the wavelength shift between the emission lines of these two isotopologues. — astro-ph.EP

Context: CO is an abundant species in comets, creating CO+ ion with emission lines that can be observed in the optical spectral range. A good modeling of its fluorescence spectrum is important for a better measurement of the CO+ abundance.

Such a species, if abundant enough, can also be used to measure the 12C/13C isotopic ratio. Aims: This study uses the opportunity of a high CO content observed in the comet C/2016 R2 (PanSTARRS), that created bright CO+ emission lines in the optical range, to build and test a new fluorescence model of this species and to measure for the first time the 12C/13C isotopic ratio in this chemical species with ground-based observations.

Methods: Thanks to laboratory data and theoretical works available in the scientific literature we developed a new fluorescence model both for 12CO+ and 13CO+ ions. The 13CO+ model can be used for coadding faint emission lines and obtain a sufficient signal-to-noise ratio to detect this isotopologue.

Results: Our fluorescence model provides a good modeling of the 12CO+ emission lines, allowing to publish revised fluorescence efficiencies. Based on similar transition probabilities for 12CO+ and 13CO+ we derive a 12C/13C isotopic ratio of 73±20 for CO+ in comet C/2016 R2. This value is in agreement with the solar system ratio of 89±2 within the error bars, making the possibility that this comet was an interstellar object unlikely.

Philippe Rousselot (1), Emmanuel Jehin (2), Damien Hutsemékers (2), Cyrielle Opitom (3), Jean Manfroid (2), Pierre Hardy (1 and 4) ((1) Inst. UTINAM, Besançon, France, (2) STAR Institute, Univ. Liège, Belgium, (3) Inst. for Astronomy, Univ. of Edimburgh, UK, (4) LICB, Dijon, France)

Comments: 11 pages, 8 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2311.05700 [astro-ph.EP] (or arXiv:2311.05700v1 [astro-ph.EP] for this version)
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Submission history
From: Philippe Rousselot
[v1] Thu, 9 Nov 2023 19:17:46 UTC (1,963 KB)
Astrobiology, astrochemistry

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻