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A survey of molecular line emission towards ultracompact HII regions

Hatchell, J., Thompson, M.A., Millar, T.J., Macdonald, G.H. (1998) A survey of molecular line emission towards ultracompact HII regions. Astronomy & Astrophysics Supplement Series, 133 (1). pp. 29-49. ISSN 0365-0138. (doi:10.1051/aas:1998309) (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided) (KAR id:17799)

The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided.
Official URL:
http://dx.doi.org/10.1006/10.1051/aas:1998309

Abstract

We have used the JCMT to survey molecular line emission towards 14 ultracompact HII regions (G5.89, G9.62, G10.30, G10.47, G12.21, G13.87, G29.96, G31.41, G34.26, G43.89, G45.12, G45.45, G45.47, and G75.78). For each source, we observed up to ten 1 GHz bands between 200 and 350 GHz, covering lines of more than 30 species including multiple transitions of CO isotopes, CH3OH, CH3CCH, CH3CN and HCOOCH3, and sulphuretted molecules. The number of transitions detected varied by a factor of 20 between sources; which were chosen following observations of high-excitation ammonia (Cesaroni et al. 1994a) and methyl cyanide (Olmi et al. 1993). In half our sample (the line-poor sources), only (CO)-O-17: (CO)-O-18, SO, (CS)-S-34 and CH3OH were detected. In the line-rich sources, we detected over 150 lines, including high excitation lines of CH3CN, HCOOCH3; C2H5CN, CH3OH, and CH3CCH. We have calculated the physical conditions of the molecular gas. To reproduce the emission from the line-rich sources requires both a hot, dense compact core and an ambient cloud consisting of less dense, cooler gas. The hot cores, which are less than 0.1 pc in size; reach densities of at least 10(8) cm(-3) and temperatures of more than 80 K. The line-poor sources can be modelled without a hot core by a 20-30 K, 10(5) cm(-3) cloud. We find no correlation between the size of the HII region and the current physical conditions in the molecular environment. A comparison with chemical models (Millar et al. 1997) confirms that grain surface chemistry is important in hot cores.

Item Type: Article
DOI/Identification number: 10.1051/aas:1998309
Subjects: Q Science > QB Astronomy
Divisions: Divisions > Division of Natural Sciences > Physics and Astronomy
Depositing User: R.F. Xu
Date Deposited: 09 Jul 2009 08:51 UTC
Last Modified: 16 Nov 2021 09:55 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/17799 (The current URI for this page, for reference purposes)

University of Kent Author Information

Thompson, M.A..

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Macdonald, G.H..

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