Observations of Excited State OH Masers at 6.0 and 13.4 GHz

Abstract

This is a brief report on a sensitive search for excited OH absorption and emission sources made with the Effelsberg 100 m telescope towards several compact HII regions. Our data are discussed elsewhere (Guilloteau et al., 1983) and we mainly present here our II3/2, J = 5/2 and 7/2 OH narrow emission results (masers). In the J = 5/2 state, 14 sources were observed with a typical 1 σ sensitivity of 0.2 Jy. Among 13 positive detections, 4 and may be 5 are new maser sources: G43.1, W48, K3-50, ON3 and G34.3 (?). With the exception of W3 (OH) the 6035 MHz line is always much stronger than the 6030 MHz line. Comparison with spectra published by others suggests time variability in M17, W51 and Orion A. In W3 (OH) a weak broad emission was also detected at 6049 MHz. In our j = 7/2 observations the peak to peak noise was the range 0.1 to 1 Jy. No masers were detected even in the strong 6035 MHz sources associated with M17 and W33 cont. Thus the F = 4−4 emission line in W3 (OH) seems to be really exceptional (Baudry et al., 1981).