We report HST WFPC2 observations of a field in the southern portion of the H II region M 20. The region shows a complex of ionization fronts that allow us to explore the nature of photoionized photoevaporative interfaces at somewhat lower excitation levels than seen in regions such as M 16. Of particular note in the observations is a long protrusion from the molecular cloud pointing back in the direction of the ionizing stars. This object is a pronounced example of the evaporating gaseous globules (EGGs) seen in M 16. Enhanced Hα at the head of the structure may indicate the presence of an embedded source there, but we are awaiting IR images to confirm this suggestion. In addition a jet (HH 399 - reported earlier by Cernicharo et al. 1998) is seen emerging from the molecular cloud into the interior of the H II region. This jet is important because it is propagating into the interior of the H II region, and is photoionized by radiation from the stars responsible for ionizing M 20. Because the jet is photoionized it offers a unique opportunity to look directly at the physical structure of a YSO jet rather than at the structure of the shock interactions within the jet. The jet is propagating into the low density interior of the H II region and so is only minimally distorted by such interactions. The abrupt termination of the jet indicates that it turned on quite suddenly. The jet also shows a very knotty structure, along with a number of features which appear to be jet knots but which are well off the main axis of the jet. This work is supported by NASA through support to the WFPC2 IDT.
American Astronomical Society Meeting Abstracts #194
- Pub Date:
- May 1999