MILLIMETER CONTINUUM MEASUREMENTS OF CIRCUMSTELLAR DUST AROUND VERY YOUNG LOW-MASS STARS

We investigate the question of disk formation during the protostar pha se. We build on the results of Keene and Masson (1990) whose analysis of L1551 showed the millimeter continuum emission comes from both an u nresolved circumstellar component, i.e., a disk and an extended cloud core. We model the dust continuum emission from the cloud core and sho w how it is important at 1.3 mm but negligible at 2.7 mm. Combining ne w 2.7 mm Owens Valley interferometer data of IRAS-Dense cores with dat a from the literature we conclude that massive disks are also seen tow ard a number of other sources. However, 1.3 mm data from the IRAM 30 m telescope for a larger sample shows that massive disks are relatively rare, occurring around perhaps 5% of young embedded stars. This impli es that either massive disks occur briefly during the embedded phase o r that relatively few young stars form massive disks. At 1.3 mm the me dian flux of IRAS-Dense cores is nearly the same as T Tauri stars in t he sample of Beckwith et al. (1990). We conclude that the typical disk mass during the embedded phase is nearly the same or less than the ty pical disk mass during the T Tauri phase.