STAR FORMATION IN THE GALAXY

Star formation in the Galaxy occurs on different spatial scales from single star formation events in Bok Globules to the formation of OB associations and star clusters. We review recent observations of Bok Globules and relate them to the dense NH3 cores observed in dark clouds. Recent work on the Chamaeleon I dark cloud supports quasi-static subcritical collapse models for low mass star formation. This cloud is a typical region of low mass star formation similar to the Taurus-Auriga clouds; star formation has continued in the cloud for approximately 10(7) yr, the most massive embedded stars have masses of approximately 2M., and the cloud appears to be magnetically supported in its long dimension. Supercritical collapse theories for star formation in giant molecular clouds are less certain and make few specific predictions. Accretion processes may be needed to form supercritical cores and star clusters, and would produce the power law form of the initial mass function at the high mass end. Recent observations of the Orion A giant molecular cloud are summarised. The helical magnetic field around L1641, the filamentary structure of the cloud, and the collapsed and fragmented nature of the massive Orion molecular ridge bear directly on the processes of cloud collapse. The star formation history of the cloud provides another record of the cloud collapse. Low mass star formation has occurred in the L1641 cloud for approximately 10(7) yr, and differs from Chamaeleon and Taurus-Auriga in forming slightly higher mass stars and in forming an embedded star cluster. Low mass star formation in the Orion Nebula region has paralleled that in L1641, but higher mass OB stars have formed as well. A more detailed investigation of the stellar populations around the Orion Nebula might better elucidate the cloud collapse history. The Trapezium Cluster is younger than approximately 10(6) yr and contains many low mass stars. A turn-over in the K luminosity function at K approximately 13 mag may be due to truncation of the initial mass function at M less-than-or-equal-to 1M., possibly through competition for available gas in the extremely close protostellar environment.