IRAS 16293-2422: evidence for infall onto a counterrotating protostellar accretion disk.
REMIJAN A.J. and HOLLIS J.M.
Abstract (from CDS):
We report high spatial resolution VLA observations of the low-mass star-forming 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 ∼6" and 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. also concluded rotation of a nearly edge-on disk from OVRO observations of much stronger and ubiquitous 13CO emission, but the direction of rotation is opposite to the SiO emission findings. Taken together, SiO and 13CO data suggest evidence for a counterrotating disk. Moreover, archival BIMA array 12CO data show an inverse P Cygni profile with the strongest absorption in close proximity to the SiO emission, indicating unambiguous material infall toward the counterrotating protostellar disk at a new source location within the IRAS 16293-2422 complex. The details of these observations and our interpretations are discussed.
ISM: Abundances - ISM: Clouds - ISM: Individual: Alphanumeric: IRAS 16293-2422 - ISM: Molecules - Radio Lines: ISM