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

Abstract

ABSTRACT We have used the Australia Telescope National Facility Mopra 22m millimetretelescope to search for emission from the 6 −2 -7 −1 E (85.5-GHz) and 7 2 -6 3 A − (86.6-GHz) transitions of methanol. The search was targeted towards 22 star formationregions which exhibit maser emission in the 107.0-GHz 3 1 -4 0 A + methanol transition,as well as in the 6.6-GHz 5 1 -6 0 A + transition characteristic of class II methanol masersources. A total of 22 regions were searched at 85.5 GHz resulting in 5 detections, ofwhich 1 appears to be a newly discovered maser. For the 86.6-GHz transition observa-tions were made of 18 regions which yielded 2 detections, but no new maser sources.This search demonstrates that emission from the 6 −2 -7 −1 E and 7 2 -6 3 A − transitionsis rare. Detection of maser emission from either of these transitions therefore indicatesthe presence of special conditions, different from those in the majority of methanolmaser sources. We have observed temporal variability in the 86.6-GHz emission to-wards 345.010+1.792, which along with the very narrow line width, confirms that theemission 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 masermodel of Sobolev & Deguchi (1994). Both detections and nondetections are usefulfor setting limits on the physical conditions in star forming regions which containmethanol maser emission. This has allowed us to estimate the likely ranges of dusttemperature, gas density, and methanol column density, both for typical methanolmaser sources and for those sources which also show 107.0-GHz emission. The gastemperature can also be estimated for those sources exhibiting masers at 85.5 and/or86.6 GHz.Key words: masers – stars:formation – ISM: molecules – radio lines : ISM