EXCITED-STATE OH MASERS AT 6.035 GHZ

We have discovered 52 new masers emitting at the 6.035-GHz transition of excited OH, and have reobserved 20 of the 26 previously known maser s of this type. The 72 masers are a complete sample of detections resu lting from a search towards several hundred 1.665-GHz ground-state OH masers. The excited-state masers are generally weaker than the ground- state masers, but we find in six of the 72 sources that the peak inten sity of excited-state emission is the stronger. Within the sample of 2 6 previously known masers, there were reports of large and rapid inten sity variations. We find that only a few sources in our sample are var iable on a 6-month time-scale, and in no case by more than 25 per cent . However, spectra of many sources discovered 20 years ago are now ver y different, with intensities commonly changed by factors of 2 or more . Many of the excited-state masers exhibit circular polarization indic ative of Zeeman splitting. We have used these to measure the direction and intensity of the magnetic field implied by the Zeeman pairs of fe atures. From all sources yet discovered, there appears to be an upper bound to the magnetic field intensities of 10 mG.