SiO Shocks of the Protostellar Jet HH 212: A Search for Jet Rotation

Abstract

HH 212 is a nearby (400 pc), highly collimated protostellar jet powered by a class 0 source in Orion. Our previous observations with the Submillimeter Array have shown that the inner part of the jet is well traced by SiO ( -->J = 8–7) shock emission. Here we present the observations at a higher angular resolution of ~0.35 -->'', searching for jet rotation with better resolved shock structures and kinematics. The jet has a transverse width of ~80-140 AU. The two SiO knots closest to the source are now spatially resolved into two bow shocks. The one in the south is better resolved; a precessing jet or an unseen wide-angle wind component may be required to reproduce its kinematics. Velocity gradients are seen across the tips of these two bow shocks and may arise from jet rotation. The launching radius of the jet, derived from the potential jet rotation, is 0.05-0.30 AU in the inner disk, consistent with an inner disk wind bearing strong resemblance to the X-wind. Continuum emission is detected at 850 μm toward the source and can be approximately separated into two components. One is extended with a deconvolved size of ~2 -->'' (800 AU), tracing bases around the SiO jet and probably a flattened envelope around the source. The other is compact with a deconvolved size of ~0.25 -->'' (or 100 AU), likely tracing a growing optically thick disk surrounded by an inner envelope and/or inner bases around the source.