Rotation and outflow motions in the very low-mass class 0 protostellar system hh211 at subarcsecond resolution

Abstract

HH 211 is a nearby young protostellar system with a highly collimated jet. We have mapped it in 352 GHz continuum, SiO (J = 8 - 7), and HCO+ (J = 4 - 3) emission at up to 02 resolution with the Submillimeter Array (SMA). The continuum source is now resolved into two sources, SMM1 and SMM2, with a separation of 84 AU. SMM1 is seen at the center of the jet, probably tracing a (inner) dusty disk around the protostar driving the jet. SMM2 is seen to the southwest of SMM1 and may trace an envelope-disk around a small binary companion. A flattened envelope-disk is seen in HCO+ around SMM1 with a radius of 80 AU perpendicular to the jet axis. Its velocity structure is consistent with a rotation motion and can be fitted with a Keplerian law that yields a mass of 50 15 M Jup (a mass of a brown dwarf) for the protostar. Thus, the protostar could be the lowest mass source known to have a collimated jet and a rotating flattened envelope-disk. A small-scale (200 AU) low-speed (2 km s-1) outflow is seen in HCO+ around the jet axis extending from the envelope-disk. It seems to rotate in the same direction as the envelope-disk and may carry away part of the angular momentum from the envelope-disk. The jet is seen in SiO close to 100 AU from SMM1. It is seen with a "C-shaped" bending. It has a transverse width of ≲ 40 AU and a velocity of 170 60 km s-1. A possible velocity gradient is seen consistently across its innermost pair of knots, 0.5 km s-1 at 10 AU, consistent with the sense of rotation of the envelope-disk. If this gradient is an upper limit of the true rotational gradient of the jet, then the jet carries away a very small amount of angular momentum of ≲ 5 AU km s-1 and thus must be launched from the very inner edge of the disk near the corotation radius. © 2009. The American Astronomical Society.