2006ApJ...640..842R

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.