Upper Limits On CN From Exocomets Transiting Beta Pictoris

The young (23 Myr) nearby (19.4 pc) star β Pictoris hosts an edge-on debris disk with two gas giant exoplanets in orbit around it. Many transient absorption features have been detected in the rotationally broadened stellar lines, which are thought to be the coma of infalling exocomets crossing the line of sight towards Earth.

In the Solar System, the molecule cynaogen (CN) and its associated ionic species are one of the most detectable molecules in the coma and tails of comets.

We perform a search for cyanogen in the spectra of β Pictoris to detect or put an upper limit on this molecule’s presence in a young, highly active planetary system. We divide twenty year’s worth of HARPS spectra into those with strong exocomet absorption features, and those with only stellar lines.

The high signal-to-noise stellar spectrum normalises out the stellar lines in the exocomet spectra, which are then shifted and stacked on the deepest exocomet absorption features to produce a high signal-to-noise exocomet spectrum, and search for the CN band head using a model temperature dependent cross-correlation template.

We do not detect CN in our data, and place a temperature and broadening dependent 5σ upper limit between 10¹² cm⁻² and 10¹³ cm⁻², to be compared to the typical 10⁹ – 10¹⁰ cm⁻² expected from scaling of the values in the Solar System comets.

M. A. Kenworthy, E. de Mooij, A. Brandeker, C. Opitom, F. Kiefer, A. Fitzsimmons

Comments: 9 pages, 8 figures, 1 table, accepted for publication in A and A. The paper is in a reproducible workflow repository at https://github.com/mkenworthy/BetaPicCN
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2504.14299 [astro-ph.EP] (or arXiv:2504.14299v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2504.14299
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Submission history
From: Matthew A. Kenworthy
[v1] Sat, 19 Apr 2025 13:50:42 UTC (1,405 KB)
https://arxiv.org/abs/2504.14299
Astrobiology, Astrochemistry,