IRAS 16293-2422: Evidence for Infall onto a Counter-Rotating Protostellar Accretion Disk

We report high spatial resolution VLA observations of the low-mass starforming region IRAS 16293-2422 using four molecular probes: ethyl cyanide (CH3CH2CN), methyl formate (CH3OCHO), formic acid (HCOOH), and the ground vibrational state of silicon monoxide (SiO). Ethyl cyanide emission has a spatial scale of ∼20 and encompasses binary cores A and B as determined by continuum emission peaks. Surrounded by formic acid emission, methyl formate emission has a spatial scale of ∼6and is confined to core B. SiO emission shows two velocity components with spatial scales less than 2 that map ∼2 northeast of the A and B symmetry axis. The redshifted SiO is ∼2 northwest of blueshifted SiO along a position angle of ∼135 which is approximately parallel to the A and B symmetry axis. We interpret the spatial position offset in red and blueshifted SiO emission as due to rotation of a protostellar accretion disk and we derive ∼1.4 M⊙ interior to the SiO emission. In the same vicinity, Mundy et al. (1986) also concluded rotation of a nearly edge-on disk from OVRO observations of much stronger and ubiquitous CO emission but the direction of rotation is opposite to the SiO emission findings. Taken together, SiO and CO data suggest evidence for a counter-rotating disk. Moreover, archival BIMA array CO data show an inverse P Cygni profile with the strongest absorption in close proximity to the SiO emission, indicating unambiguous material infall toward the counter-rotating protostellar disk at a new source location within the IRAS 16293-2422 complex. The details of these observations and our interpretations are discussed. Subject headings: ISM: abundances ISM: clouds ISM: individual (IRAS 162932422) ISM: molecules radio lines: ISM NASA Goddard Space Flight Center, Computational and Information Sciences and Technology Office, Code 606, Greenbelt, MD 20771 National Research Council Resident Research Associate