The rotational lines of methanol in comets Austin 1990 V and Levy 1990 XX

Details The rotational lines of methanol in comets Austin 1990 V and Levy 1990 XX The rotational lines of methanol in comets Austin 1990 V and Levy 1990 XX

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...287..647b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 287, no. 2, p. 647-665

Astronomy and Astrophysics

Astrophysics

36

Austin Comet, Cometary Atmospheres, Comets, Line Spectra, Methyl Alcohol, Rotational Spectra, Abundance, Interstellar Matter, Molecular Collisions, Molecular Excitation, Photochemical Reactions, Reaction Kinetics

Scientific paper

We have observed rotational lines of methanol in comets Austin (1990 V) and Levy (1990 XX) with the IRAM 30-m millimeter radio telecope. On comet Austin, several J(3-2) transitions around 145 GHz were detected and two J(2-1) lines near 97 GHz were marginally detected on May 25, 1990. On comet Levy, observed in the August 26-31, 1990 period, 12 lines were detected among 21 lines observed near 97, 145, 165 and 218 GHz. As a first step, the observations are interpreted using the rotational diagram method commonly used for interstellar molecular line studies. In a second step, an out-of-equilibrium model is used where the methanol rotational distribution is governed by collisions, spontaneous relaxation, and excitation of the fundamental vibrational bands by solar radiation. This model shows that the observed distribution is sensitive to the coma kinetic temperature, and suggests that the collisional region is underestimated when taking into account only collisions with water: collisions with electrons may play a major role in the excitation of methanol. The retrieved methanol production rates are 2.0 and 2.2 1027 s-1, corresponding to relative abundances of 5 and 0.9% with respect to water, for comets Austin and Levy, respectively. These abundances show that methanol is indeed an important cometary volatile, and that its abundance may vary from comet to comet.

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