Protoplanetary disk and/or bipolar outflow traced by H2O masers in IC1396N

The H2O maser connected with the young stellar object in the globule IC 139 6N has been mapped with the VLBA during its highest state of activity in 19 96 June. The spectrum of the H2O maser consisted of a dense group of strong low-velocity features near the LSR velocity of the globule, and two high-v elocity features: one redshifted to 9.3 km s(-1) and the other blueshifted to -14.1 km s(-1). The map of low-velocity features displays a remarkable c hain of at least eight maser spots located very close to a straight line ab out 15 AU in extent, with LSR velocities varying linearly along the line. T he two high-velocity features are offset from the low-velocity group by 410 and 10,000 AU for the blue and red features, respectively. We discuss thre e models that can describe the observed distribution of maser spots: a Kepl erian disk, a shock front, and a molecular outflow. The final model that we propose incorporates all three of these models: the low-velocity features arise in the Keplerian disk with maser emission excited by shock waves trav eling in the disk, while the high-velocity features arise at the root of th e molecular outflow originating from the central 4 M-circle dot young star or a protostar. The mass of the disk and its angular momentum are similar t o those of the solar system planets. It is suggested that it is a circumste llar accretion disk accumulating the excess angular momentum of the collaps ing molecular core, which may give rise to the formation of a planetary sys tem. This model can be tested by measurements of the proper motion and radi al velocity variations of the maser spots.