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arXiv · 2606.08180

Single-dish observations and non-LTE analysis of CH3OH, HCN, and CO line emission in the Oort cloud comet C/2017 K2 (PANSTARRS)

M. S. Kirsanova·Ya. N. Pavlyuchenkov·A. O. H. Olofsson·M. S. Lerner
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Abstract

We present pre-perihelion observations of methanol, carbon monoxide, and hydrogen cyanide in the Oort cloud comet C/2017 K2 (PANSTARRS), performed with the APEX 12-m and Onsala 20-m telescopes from April to July 2022. As the comets heliocentric distance decreased from 3.4 to 2.7 AU, CH3OH line intensities increased substantially (by factors of 1.1-4.0), with the most pronounced enhancement in lines with the upper-level energies Eu > 40K. In contrast, the brightness of the CO and HCN lines remained constant. We estimate the best-fit gas kinetic temperatures Tgas > 100 K and water production rate of Q(H2O)=(3-10)*10(28) 1/s. The derived methanol-to-water abundance ratio approx. 0.01-0.04, depending on the observed period. Our results demonstrate that non-LTE effects are dominant in the coma and must be accounted for to accurately derive molecular production rates. We also report weak non-thermal excitation, including potential maser activity in the CH3OH 8(0)-7(1) line.

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M. S. Kirsanova, Ya. N. Pavlyuchenkov, A. O. H. Olofsson, M. S. Lerner. 2026-06-06. Single-dish observations and non-LTE analysis of CH3OH, HCN, and CO line emission in the Oort cloud comet C/2017 K2 (PANSTARRS). https://arxiv.org/abs/2606.08180

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