CLASSIFICATION AND STATISTICAL PROPERTIES OF GALACTIC H2O MASERS

The association between galactic H2O masers and IRAS sources from the Point Source Catalog is established for 442 sources out of a list of 5 05 objects, which includes all the galactic H2O masers north of -30-de grees, known up to 1988. Using a multivariate statistical analysis on the four FIR fluxes of the associated IRAS source, galactic H2O masers are reclassified into two classes: those associated to star forming r egions (SFR, 52%) and those associated to late type stars (STAR, 45%). The remaining 3% cannot be included in either class. The present clas sification is compared with others in the literature. Distances for a large sub-sample of H2O masers are derived, using the galactic rotatio n curve for SFR and literature data for STAR.The parameters of the H2O maser emission (e.g. integrated flux, luminosity, variability), colle cted in a homogeneous way in the Arcetri H2O atlas (Comoretto et al. 1 990), and those of the associated IRAS sources (e.g. flux density, lum inosity, colours) are used to investigate, in a statistical way, the p roperties of the STAR and SFR classes. In particular, we investigate t he spatial distribution of masers both in the galactic plane and perpe ndicular to it. We also compare the H2O and IRAS luminosities, finding a good correlation. Moreover, we find that high luminosity sources sh ow low colour temperatures and vice versa. The spectral profile and va riability are then investigated by different means. Finally, the lumin osity function for each maser class is derived.