IRAS 16293−2422: Evidence for Infall onto a Counterrotating Protostellar Accretion Disk

We report high spatial resolution VLA observations of the low-massstar-forming region IRAS 16293-2422 using four molecular probes: ethyl cyanide(CH$_3$CH$_2$CN), methyl formate (CH$_3$OCHO), formic acid (HCOOH), and theground vibrational state of silicon monoxide (SiO). Ethyl cyanide emiss ion hasa spatial scale of $\sim20''$ and encompasses binary cores A and B asdetermined by continuum emission peaks. Surrounded by formic acid emission,methyl formate emission has a spatial scale of $\sim6''$and is confined to coreB. SiO emission shows two velocity components with spatial scales less than2$''$ that map $\sim2''$ northeast of the A and B symmetry axis. The redshiftedSiO is $\sim2''$ northwest of blueshifted SiO along a position angle of$\sim135^o$ which is approximately parallel to the A and B symmetry axis. Weinterpret the spatial position offset in red and blueshifted SiO emission asdue to rotation of a protostellar accretion disk and we derive $\sim$1.4M$_{\odot}$ interior to the SiO emission. In the same vicinity, Mundy et al.(1986) also concluded rotation of a nearly edge-on disk from OVRO observationsof much stronger and ubiquitous $^{13}$CO emission but the direction ofrotation is opposite to the SiO emission findings. Taken together, SiO and$^{13}$CO data suggest evidence for a counter-rotating disk. Moreover, archivalBIMA array $^{12}$CO data show an inverse P Cygni profile with the strongestabsorption in close proximity to the SiO emission, indicating unambiguousmaterial infall toward the counter-rotating protostellar disk at a new sourcelocation within the IRAS 16293-2422 complex. The details of these observationsand our interpretations are discussed.Comment: 18 pages, 5 figures, accepted for publication in the Astrophysical Journa