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We present the current activity of the Arcetri group in the field of water masers. This is mainly represented by observations with the Medicina radiotelescope, whose main outcome has been the compilation of the Arcetri Catalog and the study of time variability of selected sources. The Arcetri Catalog update reports the results of the observations carried out from January 1993 to April 2000 on a sample of 300 sources. The global properties of the complete Arcetri Catalog (including Comoretto et al. 1990, and Brand et al. 1994) are discussed. Of the 1013 sources, 937 have an IRAS counterpart within 1 arcmin from the nominal position of the maser. We establish a classification scheme based on the IRAS flux densities which allows to distinguish between water masers associated with star forming regions and late-type stars. The time variability study shows a large variety of behaviors. Generally more luminous sources present less variable emission and spectral components over a wider velocity range.
A sample of 14 water maser sources associated with young stellar objects (YSOs) has been monitored over 13 years with the Medicina 32-m antenna. The YSOs have been selected with bolometric luminosities from 20 L⊙ to 2 × 106 L⊙ with the aim of investigating the relationship between H2O maser variability and stellar mass. The results are presented in various graphical forms which allow to follow the variation of the different spectral components. In particular, four quantities have been considered in our analysis: the intensity of the maser lines as a function of time and velocity; the flux integrated over the observed velocity range as a function of time; the maximum flux ever observed at each velocity; and the frequency of occurrence of the maser emission at any given velocity.
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