Long-term variability of H2O masers in YSOs Valdettaro, R. ; Palla, F. ; Brand, J. ; Cesaroni, R. ; Comoretto, G. ; Felli, M. ; Palagi, F. Abstract Publication: Cosmic Masers: From Proto-Stars to Black Holes Pub Date: 2002 Bibcode: 2002IAUS..206...51V