ROTATION AND OUTFLOW MOTIONS IN THE VERY LOW-MASS CLASS 0 PROTOSTELLAR SYSTEM HH 211 AT SUBARCSECOND RESOLUTION

Abstract

HH 211 is a nearby young protostellar system with a highly collimated jet. We\nhave mapped it in 352 GHz continuum, SiO (J=8-7), and HCO+ (J=4-3) emission at\nup to ~ 0.2" resolution with the Submillimeter Array (SMA). The continuum\nsource is now resolved into two sources, SMM1 and SMM2, with a separation of ~\n84 AU. SMM1 is seen at the center of the jet, probably tracing a (inner) dusty\ndisk around the protostar driving the jet. SMM2 is seen to the southwest of\nSMM1 and may trace an envelope-disk around a small binary companion. A\nflattened envelope-disk is seen in HCO+ around SMM1 with a radius of ~ 80 AU\nperpendicular to the jet axis. Its velocity structure is consistent with a\nrotation motion and can be fitted with a Keplerian law that yields a mass of ~\n50+-15 Jupiter mass (a mass of a brown dwarf) for the protostar. Thus, the\nprotostar could be the lowest mass source known to have a collimated jet and a\nrotating flattened envelope-disk. A small-scale (~ 200 AU) low-speed (~ 2 km/s)\noutflow is seen in HCOP+ around the jet axis extending from the envelope-disk.\nIt seems to rotate in the same direction as the envelope-disk and may carry\naway part of the angular momentum from the envelope-disk. The jet is seen in\nSiO close to ~ 100 AU from SMM1. It is seen with a "C-shaped" bending. It has a\ntransverse width of <~ 40 AU and a velocity of ~ 170+-60 km/s. A possible\nvelocity gradient is seen consistently across its innermost pair of knots, with\n~ 0.5 km/s at ~ 10 AU, consistent with the sense of rotation of the\nenvelope-disk. If this gradient is an upper limit of the true rotational\ngradient of the jet, then the jet carries away a very small amount of angular\nmomentum of ~ 5 AU km/s and thus must be launched from the very inner edge of\nthe disk near the corotation radius.\n