CO studies of Herbig-Haro regions

Abstract: High resolution CO (J=1-0) observations of HH 7-11 in NGC 123? and the region around Lk Ha 224 in NGC 7129, using the 25m Millimeter Wave Telescope at Onsala, Sweden, have resulted in detailed maps. These dark cloud regions, forming stars of low to intermediate mass, show signs of shock excitation, identified as Herbig-Haro objects and H?0 masers. The CO emission, showing an anisotropic distribution, is observed at large velocities and appears to originate in regions, which are spatially associated with these objects. This high velocity CO gas apparently is clumpy and warmer than the ambient molecular cloud. The direction of its motion is approximately parallell to the interstellar magnetic field. Around the young star Lk Ha 234 the presence of a rotating gaseous disk is indicated , having the size of the solar system and being able to collimate the CO flow. It appears unlikely that radiation from the central young stars alona can provide the energy and the momentum carried by the CO flows. It also appears improbable that the mass loss rates needed to drive the flows can be maintained by the stars in a steady state through a stellar wind. Several arguments are presented in favour of a hybrid model, in which short-lived massive ejections are followed by longer periods of quiescence characterized by continuous mass loss at lower rates, compatible with those inferred from optical spectra of young stars. In addition, a model for the geometry of the CO flows is presented , which also links together the high velocity molecular gas with the Herbig-Haro objects in a natural way.