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

Abstract

We report high spatial resolution VLA observations of the low-mass star-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 the ground vibrational state of silicon monoxide (SiO). Ethyl cyanide emiss ion has a spatial scale of $\sim 20^{\prime \prime }$ 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 $\sim 6^{\prime \prime }$and is confined to core B. SiO emission shows two velocity components with spatial scales less than 2${}^{\prime \prime }$ that map $\sim 2^{\prime \prime }$ northeast of the A and B symmetry axis. The redshifted SiO is $\sim 2^{\prime \prime }$ northwest of blueshifted SiO along a position angle of $\sim 135^o$ 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 $\sim$1.4 M${}_{\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 observations of much stronger and ubiquitous ${}^{13}$CO emission but the direction of rotation is opposite to the SiO emission findings. Taken together, SiO and ${}^{13}$CO data suggest evidence for a counter-rotating disk. Moreover, archival BIMA array ${}^{12}$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.

arXiv comment18 pages, 5 figures, accepted for publication in the Astrophysical Journal

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