OH masers and the nature of massive star-forming regions

Abstract

We briefly review some of the observational characteristics of intense OH masers in massive star-forming regions, and discuss the physical characteristics of the zone in which masers form. We describe a detailed model of the maser zone and outline its predictions for the physical conditions of number density, temperature and bulk motions for 1665, 1667, 1720, 1612, 6035 and 4765 MHz masers. We find, for example, that intense 1665 MHz spots are indicative of cold (<75 K), accelerating flowing regions. Results of a similar nature are given for the other frequencies. We also analyse in detail a specific region in W3(OH) which shows spatial superposition of masers at 4765, 1720 and 1665 MHz. We also demonstrate the influence of velocity redistribution and present some preliminary results on the origin of maser polarization.