Outflows in High Mass Star-Forming Regions

Abstract

In the last decade, observations of star-forming regions in the millimeter wavelength range have led to the discovery of supersonic molecular outflows from embedded infrared sources, a heretofore unsuspected, but now generally accepted, phase in the star formation process. In order to better understand the outflow phenomenon in high mass (i.e., high luminosity) pre-main sequence stars, the three sources S87, LkHα101, and S106 were chosen for closer study. Observations from the recently completed Owens Valley Radio Observatory's millimeter wave interferometer afford us the highest spatial-resolution, molecular line (CS J=2→1 and 13CO J=1→0) maps of these sources to date. The OVRO maps were combined with data from the 14 m FCRAO millimeter wave radio telescope, the VLA, IRAS, and the Palomar 5 m and 1.5 m optical telescopes. A synthesis of the data reveals that although all three pre-main sequence objects are the sources of powerful, ionized stellar winds, only one, S87/IRS1, currently drives a bipolar molecular outflow. The inferred mass loss rates in the winds of S87/IRS1, LkHα101, and S106 IR are 1.8 x 10-5, 1.7 x 10-6, 1.1 x 10-5 M☉ yr-1, with corresponding wind velocities of 160, 350, and 200 km s-1. In all cases the wind velocities are lower, and the mass loss rates higher, than for main sequence stars of the same spectral types. Radiation pressure is inadequate to drive these winds, which can be anisotropic in their velocity fields. The existence of massive, large-scale (r ≈ 1016 cm) disks, necessary for numerous proposed molecular outflow models, can now be ruled out. Only one of the many proposed molecular outflow models is consistent with the new observations (Konigl 1982). Although the observed winds can disperse a good portion of the cloud cores they inhabit, they cannot completely destroy these cores. Consequently, outflows from pre-main sequence stars alone cannot account for the dispersal of molecular clouds, as some investigators have suggested. Two glaring and intriguing problems remain to be solved in this field: the origin of the supersonic turbulence observed throughout a molecular cloud, and the driving mechanism of the powerful, ionized winds found in the high-mass, pre-main sequence stars.