Ammonia and other parent molecules in comet 10P/Tempel 2 from Herschel/HIFI and ground-based radio observations

TL;DR

This study reports the detection of ammonia and other molecules in comet 10P/Tempel 2 using Herschel and ground-based telescopes, revealing molecular abundances, hyperfine structure, and anisotropic outgassing over multiple returns.

Contribution

First detection of ammonia hyperfine structure in a comet and comprehensive molecular abundance analysis across two returns.

Findings

Ammonia abundance is about 0.5%, similar to other comets.

Hyperfine structure of ammonia line is resolved for the first time.

Strong anisotropic outgassing observed in all data sets.

Abstract

The Jupiter-family comet 10P/Tempel 2 was observed during its 2010 return with the Herschel Space Observatory. We present here the observation of the (J, K) = (1, 0)-(0, 0) transition of ammonia at 572 GHz in this comet with the Heterodyne Instrument for the Far Infrared (HIFI) of Herschel. We also report on radio observations of other molecules (HCN, CH3OH, H2S and CS) obtained during the 1999 return of the comet with the CSO telescope and the JCMT, and during its 2010 return with the IRAM 30-m telescope. Molecular abundances relative to water are 0.09%, 1.8%, 0.4%, and 0.08% for HCN, CH3OH, H2S, and CS, respectively. An abundance of 0.5% for NH3 is obtained, which is similar to the values measured in other comets. The hyperfine structure of the ammonia line is resolved for the first time in an astronomical source. Strong anisotropy in the outgassing is present in all observations from 1999 to 2010 and is modelled to derive the production rates.