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2004MNRAS.351.1327C - Mon. Not. R. Astron. Soc., 351, 1327-1337 (2004/July-2)
Search for class II methanol masers at 23.1 GHz.
CRAGG D.M., SOBOLEV A.M., CASWELL J.L., ELLINGSEN S.P. and GODFREY P.D.
Abstract (from CDS):
A maser model in which methanol molecules are pumped to the second torsionally excited state by radiation from warm dust can account for class II maser activity in all the transitions in which it is observed. According to this model the 23.1-GHz maser is favoured by conditions representing low gas temperature, high external dust temperature, low gas density and high column density of methanol; the scarcity of this maser indicates that such combinations of conditions are uncommon. We have undertaken new model calculations to examine the range of parameters compatible with the upper limits on 23.1-GHz emission from our survey. Further constraints apply in sources with upper limits to maser emission at 107.0 GHz and the combination of data for the two transitions delineates a narrow range of gas density and methanol abundance if the dust temperature is 175 K or greater. While the results are subject to the uncertainties of the chosen model, they may be applicable to the majority of methanol maser sites in the vicinity of newborn high-mass stars, in which methanol masers other than the 6.6- and 12.1-GHz transitions are not detected.
Abstract Copyright: 2004 RAS
Journal keyword(s): masers - stars: formation - ISM: molecules - radio lines: ISM
Simbad objects: 54
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