A search for 4750- and 4765-MHz OH masers in southern star-forming regions |
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Authors: | R G Dodson S P Ellingsen |
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Institution: | School of Mathematics and Physics, University of Tasmania, GPO Box 252-21, Hobart, Tasmania 7001, Australia |
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Abstract: | We have used the Australia Telescope Compact Array (ATCA) to make a sensitive (5 σ ?100 mJy) search for maser emission from the 4765-MHz 2Π1/2 F =1→0 transition of OH. 55 star formation regions were searched and maser emission with a peak flux density in excess of 100 mJy was detected toward 14 sites, with 10 of these being new discoveries. In addition we observed the 4750-MHz 2Π1/2 F =1→1 transition towards a sample of star formation regions known to contain 1720-MHz OH masers, detecting marginal maser emission from G348.550?0.979. If confirmed this would be only the second maser discovered from this transition. The occurrence of 4765-MHz OH maser emission accompanying 1720-MHz OH masers in a small number of well-studied star formation regions has led to a general perception in the literature that the two transitions favour similar physical conditions. Our search has found that the presence of the excited-state 6035-MHz OH transition is a much better predictor of 4765-MHz OH maser emission from the same region than 1720-MHz OH maser emission is. Combining our results with those of previous high-resolution observations of other OH transitions we have examined the published theoretical models of OH masers and find that none of them predicts any conditions in which the 1665-, 6035- and 4765-MHz transitions are inverted simultaneously. |
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Keywords: | masers stars: formation ISM: molecules radio lines: ISM |
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