Molecular outflows and 1000 AU structure of low mass YSO envelopes

Abstract

We present the results of an observational study into the molecular outflows and small scale ( ~ 1000 AU) envelope structure of a sample of nine low mass young stellar objects (YSOs) in Taurus. The characteristics of the outflows are derived from ^(12)CO J = 3 - 2 mapping with the James Clerk Maxwell Telescope, while the envelopes are imaged in the HCO^+ 1-0, ^(13)CO 1- 0 and C^(18)O 1-0 emission lines with the Owens Valley Millimeter Array. Using dust envelope continuum fluxes at 1 mm as the basis for an evolutionary ordering, a picture emerges in which the mass, extent, and collimation of outflows decreases over time as the envelopes become less massive, the opening angle of the outflow cavity increases, and mass accretion through the disk slows down. On 1000 AU scales the HCO+ and ^(13)CO/C^(18)O emission in the envelope is closely related to the outflow cavity, often outlining the cavity walls. In addition, the envelopes are clumpy, and two sources appear surrounded by an incomplete ring or torus, 1500-3000 AU in radius. The role of the outflow in shaping the small scale molecular emission may be passive (creating a low-opacity pathway for heating radiation) rather than, or in addition to, active (compressing and shock-heating the material).