IngentaConnect A search for 85.5- and 86.6-GHz methanol maser emission

Abstract:

We have used the Australia Telescope National Facility Mopra 22-m millimetre telescope to search for emission from the 85.5-GHz 6_-2-7_-1 E and 86.6-GHz 7₂-6₃ A^- transitions of methanol. The search was targeted towards 22 star formation regions which exhibit maser emission in the 107.0-GHz 3₁-4₀ A⁺ methanol transition, as well as in the 6.6-GHz 5₁-6₀ A⁺ transition characteristic of class II methanol maser sources. Each of these regions was searched at 85.5 GHz, resulting in five detections, of which one appears to be a newly discovered maser. For the 86.6-GHz transition, observations were made of 18 regions, which yielded two detections, but no new maser sources. This search demonstrates that emission from the 6_-2-7_-1 E and 7₂-6₃ A^- transitions is rare. Detection of maser emission from either of these transitions therefore indicates the presence of special conditions, different from those in the majority of methanol maser sources. We have observed temporal variability in the 86.6-GHz emission towards 345.010+1.792, which – along with the very narrow line width – confirms that the emission is a maser in this source.

We have combined our current observations with published data for the 6.6-, 12.1-, 85.5-, 86.6-, 107.0-, 108.8- and 156.6-GHz transitions for comparison with the maser model of Sobolev & Deguchi. Both detections and non-detections are useful for setting limits on the physical conditions in star-forming regions which contain methanol maser emission. This has allowed us to estimate the likely ranges of dust temperature, gas density and methanol column density, both for typical methanol maser sources and for those sources which also show 107.0-GHz emission. The gas temperature can also be estimated for those sources exhibiting masers at 85.5 and/or 86.6 GHz.

Keywords: masers; stars: formation; ISM: molecules; radio lines: ISM

Document Type: Research article

DOI: 10.1046/j.1365-8711.2003.06788.x

Affiliations: 1: School of Mathematics and Physics, University of Tasmania, Private Bag 21, Hobart, Tasmania 7001, Australia 2: School of Chemistry, Building 23, Monash University, Victoria 3800, Australia 3: Department of Astrophysics and Optics, School of Physics, University of New South Wales, NSW 2052, Australia 4: Department of Engineering Physics, University of Wollongong, Northfields Avenue, NSW 2522, Australia

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