The origin of the protostellar jet GGD 34 ?

GGD 34 is a protostellar jet with wiggles which are accompanied by “sine-like” variations in the radial velocity of the emitting material by as much as 60 km s−1. Thus GGD 34 is an interesting object to understand the physical mechanisms involved in the generation of wiggles in protostellar jets. In this work we present high resolution images obtained with the Canada-France-Hawaii Telescope (CFHT) which shows that GGD 34 consists of a narrow (unresolved) jet roughly bisecting an extended faint envelope. The [S II] emission from the working surface has an arrow shaped morphology; the body of the jet is clearly distinguished as well as two backtails disposed in an approximately symmetric manner with respect to the jet axis. The Hα emission is concentrated at the head of the jet indicating that the gas is significantly more excited at this location (in particular at the so-called Knot 5); we suggest that Knot 5 traces the location of the Mach disk since spectra of GGD 34 indicate that it is a light beam of gas. The high resolution images also show that the envelope around GGD 34 connects smoothly with the back tails at the head of the jet. We speculate whether it traces the backflow; the expected backflow velocity is shown to be ∼ 32 km s−1 which is consistent with the degree of excitation of the envelope. However, an accurate determination of the proper motion of the head is necessary to check whether this interpretation is correct. We also present radiocontinuum (3.6 and 6 cm) VLA observations and report the detection of a radio source close to the apex of the cavity from which the jet emerges. This radio source has a spectral index of 0.7±0.5, consistent within error with the value of 0.6 expected for a thermal jet. We suggest that this radio object is associated with the source of the outflow. Additional 12CO(3–2) observations obtained with the JCMT show molecular gas redshifted by ∼ 2.5 km s−1 with respect to the cloud at this location.