IRAS 16293−2422: Proper Motions, Jet Precession, the Hot Core, and the Unambiguous Detection of Infall

Abstract

We present high spatial resolution observations of the multiple protostellar system IRAS 16293-2422 using the Submillimeter Array (SMA) at 300 GHz and the Very Large Array (VLA) at frequencies from 1.5 to 43 GHz. This source was already known to be a binary system with its main components, A and B, separated by ∼5″. The new SMA data now separate source A into two submillimeter continuum components, which we denote Aa and Ab. The strongest of these, Aa, peaks between the centimeter radio sources A1 and A2, but the resolution of the current submillimeter data is insufficient to distinguish whether this is a separate source or the centroid of submillimeter dust emission associated with A1 and A2. Archival VLA data spanning 18 yr show proper motion of sources A and B of 17 mas yr -1 1, associated with the motion of the ρ Ophiuchi cloud. We also find, however, significant relative motion between the centimeter sources A1 and A2, which excludes the possibility that these two sources are gravitationally bound unless A1 is in a highly eccentric orbit and is observed at periastron, the probability of which is low. A2 remains stationary relative to source B, and we identify it as the protostar that drives the large-scale northeast-southwest CO outflow. A1 is shock-ionized gas that traces the location of the interaction between a precessing jet and nearby dense gas. This jet probably drives the large-scale east-west outflow, and indeed its motion is consistent with the wide opening angle of this flow. The origin of this jet must be located close to A2 and may be the submillimeter continuum source Aa. Thus, source A is now shown to comprise three (proto)stellar components within 1″. Source B, on the other hand, is single, exhibits optically thick dust emission even at 8 GHz, has a high luminosity, and yet shows no sign of outflow. It is probably very young and may not even have begun a phase of mass loss yet. The SMA spectrum of IRAS 16293-2422 reports the first astronomical identification of many lines of organic and other molecules at 300 and 310 GHz. The species detected are typical of hot cores, the emission from which is mainly associated with source A. The abundances of second-generation species, especially of sulphur-bearing molecules, are significantly higher than predicted by chemical models for this source to date, and we suggest that shocks are probably needed to explain these enhancements. The peaks in the integrated emission from molecules having high rotation temperatures coincide with the centimeter source A1, also highlighting the key role of shocks in explaining the nature of hot cores. Finally, we use the high brightness temperature of the submillimeter dust emission from source B to demonstrate the unambiguous detection of infall by observing redshifted SO (7 7 -6 6 ) absorption against the emission from its dust disk. © 2005. The American Astronomical Society. All rights reserved.