Excited OH 4.7-GHz masers associated with IRAS far-infrared sources

Abstract

A sample of 44 sources has been searched for maser emission from excited OH in the 2Π1/2 J=1/2 state, in the three lines at 4765, 4750 and 4660 MHz. Most of the objects searched were taken from the large sample of powerful far-infrared sources previously searched for OH 18-cm emission by Cohen, Baart & Jonas. Nine sources were detected at 4765 MHz, including two new discoveries. Three of these sources were detected at 4750 MHz, including the first strong 4750-MHz maser, and two of the sources were detected at 4660 MHz. Strong variations were observed in four previously known 4765-MHz maser sources. The implication of these results for the excitation of OH and the pumping of OH masers is briefly discussed.