Radio continuum-H2O maser systems in NGC 2071: H2O masers tracing A jet (IRS 1) and A rotating proto-planetary disk of radius 20 AU (IRS 3)

We have observed simultaneously the 1.3 cm continuum and H2O maser emission toward the core of the star-forming region NGC 2071 using the Very Large Array in its A configuration. Two 1.3 cm continuum sources have been detected in the region, coinciding with the infrared sources 1RS 1 and 1RS 3, respectively. The radio emission in 1RS 3 is consistent with an ionized thermal bipolar radio jet. Two clusters of H2O maser spots are detected, one associated with 1RS 1 (22 spots) and the other one associated with 1RS 3 (13 spots). The H2O maser distribution in 1RS 1 seems to be tracing at scales of 300 AU the larger scale H2 outflow observed at a few thousands of AU from the exciting source. On the other hand, the H2O masers in 1RS 3 are distributed as an apparent disk of ≃0″05 (≃20 AU) radius, oriented almost perpendicular to the major axis of the radio jet. There is a clear velocity gradient (≃0.35 km s-1 AU-1) along the major axis of the H2O maser distribution, which can be gravitationally bound by a central mass of ≃ 1 M⊙. These results, together with the low-mass and early evolutionary stage of IRS 3, suggest that masers around this source are tracing a rotating proto-planetary disk within a proto-solar-like system. This represents direct kinematic evidence of the smallest rotating circumstellar disk ever observed around a young stellar object (YSO). We discuss the dichotomy of H2O masers tracing either outflows or disks around YSOs, based on the evolutionary scheme proposed in our earlier work. We suggested that systems in which H2O masers trace disks are less evolved than those in which masers trace outflows. In this scheme, IRS 3 would then represent a relatively less evolved object than IRS 1. This prediction is consistent with independent infrared observations showing that IRS 3 is at an earlier phase of evolution. © 1998. The American Astronomical Society. All rights reserved.