OBSERVATIONS OF COLD IRAS SOURCES IN THE 18-CM OH LINES

The results of observations of OH sources from the IRAS Catalog showing intense far IR emission, but are optically invisible and related to cold dense clouds, are presented. The observations were conducted in June 1991 with the Large Radio Telescope at Nancy, France; both main and satellite 18-cm lines of the OH molecule were observed. The detected OH maser source G16.9-2.2 emits intensively in the 1665 and 1667 MHz main lines. The line profiles a display of narrow emission features with strong circular polarization, which is typical of type 1 OH maser sources related to the region of active star formation. The peak flux density of the observed masers is less than 1% of IR flux density at 60 and 100 mum wavelengths of the related IR source. This is evidence that far IR emission may pump OH masers in star formation regions.