Global star formation in the L1630 molecular cloud

The results of a study of dense cores and star formation in the L1630 (Orion B) molecular cloud are presented. Unbiased, well sampled, systematic surveys for density condensations and embedded infrared sources in the L1630 cloud were completed in an attempt to understand the relationship between dense cores and young stars. To identify the dense cores, L1630 was surveyed in the J=2-1 transition of CS using a 7-m telescope. Thirteen thousand positions were surveyed with 1 degree spacing to an rms noise level of 0.2 K. The total area covered was approximately 3.6 square degrees. Emission was detected over 10 percent of the area surveyed and this emission is not uniformly distributed throughout the cloud but is confined in 42 dense cores. A 2.2 micron survey of a significant portion of the L1630 cloud was carried out using an infrared array camera on a 1.3-m telescope. Three thousand 1 degree x 1 degree fields were surveyed, covering an area of approximately 0.8 square degrees. These regions included both areas containing CS emission and areas without CS emission. The completeness limit of this survey is estimated to be 13th magnitude at K (approximately 0.16 solar mass main sequence dwarf). As a result, four embedded infrared clusters were identified. These embedded clusters contain at least 58 percent but possibly as much as 96 percent of the total number of sources associated with this molecular cloud suggesting that the dominant mode of star formation in this region is in clusters. The CS and 2.2 micron surveys of L1630 provided the first census of dense cores and young stellar objects within a molecular cloud. A comparison of these surveys clearly shows that star formation in the region surveyed occurs exclusively in the dense gas. It is shown that the star formation in L1630 is a highly localized process both within the molecular cloud and within the dense gas