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arXiv · 1602.03488

Measuring the Distribution and Excitation of Cometary CH3OH Using ALMA

M. A. Cordiner·S. B. Charnley·M. J. Mumma·D. Bockelée-Morvan·N. Biver·G. Villanueva·L. Paganini·S. N. Milam·A. J. Remijan·D. C. Lis·J. Crovisier·J. Boissier·Y. -J. Kuan·I. M. Coulson
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Abstract

The Atacama Large Millimeter/submillimeter Array (ALMA) was used to obtain measurements of spatially and spectrally resolved CH$_3$OH emission from comet C/2012 K1 (PanSTARRS) on 28-29 June 2014. Detection of 12-14 emission lines of CH$_3$OH on each day permitted the derivation of spatially-resolved rotational temperature profiles (averaged along the line of sight), for the innermost 5000 km of the coma. On each day, the CH$_3$OH distribution was centrally peaked and approximately consistent with spherically symmetric, uniform outflow. The azimuthally-averaged CH$_3$OH rotational temperature ($T_{rot}$) as a function of sky-projected nucleocentric distance ($\rho$), fell by about 40 K between $\rho=0$ and 2500 km on 28 June, whereas on 29 June, $T_{rot}$ fell by about 50 K between $\rho=$0 km and 1500 km. A remarkable ($\sim50$ K) rise in $T_{rot}$ at $\rho=$1500-2500 km on 29 June was not present on 28 June. The observed variations in CH$_3$OH rotational temperature are interpreted primarily as a result of variations in the coma kinetic temperature due to adiabatic cooling, and heating through Solar irradiation, but collisional and radiative non-LTE excitation processes also play a role.

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M. A. Cordiner, S. B. Charnley, M. J. Mumma, D. Bockelée-Morvan, N. Biver, G. Villanueva, L. Paganini, S. N. Milam, A. J. Remijan, D. C. Lis, J. Crovisier, J. Boissier, Y. -J. Kuan, I. M. Coulson. 2016-02-10. Measuring the Distribution and Excitation of Cometary CH3OH Using ALMA. https://arxiv.org/abs/1602.03488

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