Water Masers as Tracers of Protostellar Disks and Outflows in the Intermediate Mass Star Forming Region NGC 2071

Abstract

We have mapped the water maser emission associated with the infrared centers IRS1 and IRS3 of the NGC 2071IR star forming region at four epochs over ~4 months with the Very Long Baseline Array (VLBA). We detected 269 maser features with ~1 km/sec linewidths and measured 30 proper motions. In each infrared center, the water maser emission appears to trace parts of a protostellar disk and collimated outflow. The disk components are ~9 and ~17 AU long, in IRS3 and IRS1 respectively, and ~2 AU wide. They are identified as disks by their compact size, elongation parallel to the direction of known IR polarization, central location in the maser maps, small internal proper motions, and proximity to 1.3 cm continuum emission. The outflows have axes perpendicular to the disks and exhibit proper motions of up to ~42 km/sec. They are outlined by maser emission up to ~260 AU from the protostars. The IRS3 outflow appears to be conical on one side, while the IRS1 outflow comprises a narrowly collimated bipolar flow surrounded by outward-facing, funnel-shaped cavities. The detection of water maser emission tracing such compact disk components and specifically conical or funnel-shaped structures is unusual. The fact that the distributions are similar in IRS3 and IRS1 may indicate the two infrared centers are roughly coeval. NGC 2071IR provides a rare opportunity to resolve the structures and dynamics of disks and outflows together, and to do so for two protostars that are only ~2000 AU apart (in projection) in a deeply embedded star forming region of intermediate luminosity.