The maser source S140-H2O as a protoplanetary disk

We present the observations of the H2O maser in S140 with the 22-m radio te lescope of the Pushchino Radio Astronomy Observatory in 1992-1999. The H2O maser emission is mainly concentrated in three symmetrically placed narrow radial-velocity intervals. In contrast to our earlier observations (1981-19 91), we did not detect emission simultaneously in all three intervals; inst ead, the emission appeared successively in each. We discuss possible origin s for this behavior. To explain the flux variability and radial-velocity dr ift of the main components, we propose a model with Keplerian orbital motio n of clumps (protoplanets) and calculate their orbital parameters. (C) 2001 MAIK "Nauka/Interperiodica".