| Summary. We report positions and spectra of 22 water vapor sources near H II regions and molecular clouds. Fifteen of the H20 sources are new discoveries. The H2O maser in NGC 1333 is aligned with a row of Herbig-Haro objects. The H20 emission in OMC2 probably comes from the shell of a recently- formed B star of 5 M0. This may be about the smallest mass of early-type stars whose circumstellar H20 emission is above our current limit of detection. The H2O source in 5140 has a broad triple spectrum, and coincides with a single, strong infrared source. The object is probably a young BO.5 star with a hot, thick envelope expanding at a velocity of 14 km/s The mean duration of the H2O phase of star formation, for stars earlier than Bl, is 7 10^4 yr. There are therefore about 2000 H2O sources in the Galaxy, with H2O luminosities >16-8 L0. Here we assume that H2O sources are located mainly in the vicinity of compact H II regions. The distribution of H2O masers along the galactic plane has strong concentrations near l = 12, 320, and 470 deg, and possibly toward the corresponding longitudes in the southern hemisphere. The concentrations at l = 32 and 470 deg are matched by similar enhancements in the radio continuum or in CO line intensity, and probably indicate two major spiral arms. There appears to be a deficiency of H2O sources within 500 pc of the galactic center. Key words: H2O masers - star formation - infrared sources - galactic structure |
