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24th of February 2020
ATCA OH Maser observations for the SPLASH Survey
by Qiao et al.
Ground-state OH masers are relatively common in the vicinity of high-mass star formation (HMSF), the circumstellar envelopes of evolved giant and supergiant stars, and the interaction regions of supernova remnants (SNRs) and their surrounding molecular clouds. OH masers associated with HMSF regions are primarily from the main line transitions, i.e., 1665 and 1667 MHz, whereas evolved star OH masers are predominantly strong in the 1612 MHz transition. Qiao et al. present high spatial resolution ATCA observations of ground-state OH masers identified in the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH). Comparison between these 362 maser sites with information presented in the literature allowed categorizations of 238 sites (66%) as evolved star sites, 63 (17%) as star formation, 8 (2%) as supernova remnants and 53 (15%) as unknown maser sites (15%).

The Figure above presents a Venn diagram of the total sample of 629 evolved star sites, showing the overlap between the four ground-state OH transitions in the full SPLASH survey region. There are no solitary 1665 or 1720 MHz OH masers, but solitary 1612 MHz masers are common, and there are three instances of solitary 1667 MHz maser sources. The 1720 MHz line is only detected towards two sites. Overall the largest overlap is between 1612 and 1667 MHz OH masers, with 93% (89/96) of 1667 MHz OH maser sites also exhibiting 1612 MHz detections. 1612 and 1665 MHz OH masers have the second largest overlap: 90% (37/41) of evolved star 1665 MHz OH masers show a 1612 MHz counterpart. More details are given in the paper to be published in Monthly Notices of the Royal Astronomical Society.

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