The Arcetri Catalog of H2O maser sources: Update 2000

We present a second update of the Arcetri Catalog of water masers (Comorett o et al. 1990; Brand et al. 1994). The present study reports the results of the observations carried out with the Medicina 32-m radiotelescope from Ja nuary 1993 to April 2000 on a sample of 300 sources. This compilation consi sts of newly discovered maser sources that did not appear in the previous A rcetri Catalogs and is made of: a) detections from the literature, and b) u npublished detections obtained with the Medicina antenna. Overall, 83 out o f 300 sources were detected. The detection rate is low (28%) and we attribu te this result to the inclusion in our survey of a rather large number of s purious maser detections that have appeared in one particular paper. The ob servational parameters are reported in tabular form for all the 300 sources and the spectra of the detected masers are presented. We discuss the globa l properties of the complete Arcetri Catalog based on Comoretto et al. (199 0), Brand et al. (1994) and the present observations, which now contains 10 13 galactic water maser sources. Of these, 937 have an IRAS counterpart wit hin 1 arcmin from the nominal position of the maser. We establish a classif ication scheme based on the IRAS flux densities which allows to distinguish between water masers associated with star forming regions and late-type st ars. The Arcetri Catalog represents a useful data base for systematic studi es of galactic water maser sources.