GIANT HERBIG—HARO FLOWS IN L1228: A SECOND LOOK

摘要

We present second epoch narrowband Hα and SH images of the giant Herbig-Haro flows HH199 and HH200 inthe L1228 molecular cloud. Proper motions for several members of the HH200 flow were determined by comparingthe new images to similar narrowband images taken 13 years earlier. Based on our measurements, the HH200 flow isinclined by 15° to the plane of the sky and has a steady, fixed outflow axis with P.A. = 49°. There is a general nonlineardecline in the proper motions with increasing distance from the source, and it appears that successive eruptionepisodes have cleared out a relatively free channel through the L1228 cloud. The bright knot HH200B6 is locatedat the end of the channel along the edge of L1228, and appears to be tracing the location where the outflow eruptsfrom the cloud. We did not detect any proper motions for HH200B6, and suggest that it is the plug of material thathas been bored out by the cumulative effects of numerous eruptions along a steady outflow axis. The proper motionscombined with the spacing of the HH200 knots along the flow axis are consistent with a velocity variable outflow,which erupts periodically on timescales of the order of 600 years. The relatively small size of the knots combinedwith the large proper motions and derived bow-shock speeds would seem to rule out the presence of a less collimatedwind component. We also discuss the HH199 flow, which is radically different from HH200. The members of theHH199 flow exhibited large changes in the morphology and emission, and were not suitable for determiningproper motions. The HH200 and HH199 flows appear to be the opposite ends of the spectrum of giant HH flows.