1999ApJ...526..236S

The H₂O maser connected with the young stellar object in the globule IC 1396N has been mapped with the VLBA during its highest state of activity in 1996 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-velocity 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 chain of at least eight maser spots located very close to a straight line about 15 AU in extent, with LSR velocities varying linearly along the line. The 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 three models that can describe the observed distribution of maser spots: a Keplerian 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 traveling in the disk, while the high-velocity features arise at the root of the molecular outflow originating from the central 4 M_☉ young star or a protostar. The mass of the disk and its angular momentum are similar to those of the solar system planets. It is suggested that it is a circumstellar accretion disk accumulating the excess angular momentum of the collapsing molecular core, which may give rise to the formation of a planetary system. This model can be tested by measurements of the proper motion and radial velocity variations of the maser spots.