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Session 53 - Circumstellar Disks & Outflows Associated with YSOs.
Oral session, Tuesday, January 14
Piers 4/5,
The resolved imaging of compact optical circumstellar nebulae associated with young stars in the Trapezium cluster is one of the most exciting results obtained with the Hubble Space Telescope (O'Dell amp; Wen 1994, ApJ 436, 194; O'Dell, Wen amp; Hu, 1993, APJ 410, 696). These data, in combination with ground-based near-infrared images (McCaughrean amp; Stauffer 1994, AJ 108,1382) suggest that a very large fraction (>50%) of stars in the Trapezium cluster have circumstellar disks. Special interest in such disks arises from their potential role in the formation of planetary systems. Evidence for planetary system formation rests largely upon assessments of the mass in disks. Previous attempts to measure disk masses in the Trapezium have resulted only in upper limits of < 0.15 solar masses (Mundy, Looney amp; Lada 1995 ApJL 462,137), an order of magnitude higher than estimates of the minimum mass solar nebula. We present new millimeter continuum observations from the IRAM interferometer of 2 fields in the Trapezium cluster. The sensitivity of our observations, permits the detection (at 9\sigma) of disks with masses \sim 0.005 solar masses, more than an order of magnitude smaller than previous interferometer observations of this cluster and sufficiently sensitive to detect the minimum mass solar nebula. As a result, we detected three sources, coincident with both identified near-infrared sources and proplyds, and estimate disk masses ranging from 0.007 to 0.016 solar masses. In addition to these 3 detections, 12 proposed disk systems or proplyds that were within our observed fields were not detected. The implications of our results for possible planet formation will be discussed.
