Masers of the first type are beacons of star formation sites, and allow one to explore the environment of deeply embedded sources, completely inaccessible at optical and near-infrared wavelengths. Stellar masers are observed to obtain knowledge of the spatial- and velocity structure of the stellar envelopes and to study their variability. The availability of a catalog, in which all known water masers are brought together is an important aid to these studies, in that it greatly facilitates the selection of objects on which to perform more detailed studies. The Arcetri catalog is such a data base. Thus, maser variability studies on long time scales can also be performed.
Work is in progress to be more quantitative.
We have detected water emission in 83 sources, and their spectra, including multiple observations of the same source, are presented in Sect. The global properties of the Catalog are discussed in Sect.