Elizabeth A. Lada

Constraints on Circumstellar Disk Masses in the Trapezium Cluster

We present λ = 3.5 mm continuum observations of the Trapezium Cluster core obtained with the BIMA array with 18 × 10 resolution. Sixteen sources are detected at the 4 σ or greater level within a 45 radius of field center. Four of these sources are coincident with previously proposed star-disk systems that show centimeter wavelength emission; their millimeter emission is consistent with the extrapolated free-free emission. Three additional sources are near stellar positions from a larger near-infrared survey. The nature of these sources and the remaining nine sources without stellar counterparts is uncertain. Considering the large number of proposed star-disk systems within our field (33) and the even larger number of cluster stars in the field (108), we conclude that massive circumstellar disks are not common in this cluster. Converting our flux limits to mass estimates, we restrict disk masses around individual sources to be ≤0.15 M☉. Statistical analysis of the overall sample of possible sources suggests that the average disk mass is ≤0.03 M☉. These limits are not sufficiently strict to rule out the possibility that disks in the Trapezium Cluster have a similar mass distribution to those associated with stars forming in isolation or loose aggregates.

Mapping Dust Extinction with IR Cameras

In this paper we describe a powerful method for using data obtained in large scale, multi-wavelength, infrared imaging surveys to directly measure and map the distribution of extinction through a molecular cloud. This method combines measurements of near-infrared color excess and certain techniques of star counting to derive mean extinctions through a cloud at higher angular resolutions and greater optical depths than those achieved previously by optical star counting.