Massive Protoplanetary Disks in the Trapezium Region

Abstract

We determine the disk mass distribution around 336 stars in the young (~1 Myr) Orion Nebula cluster by imaging a 25 × 25 region in 3 mm continuum emission with the Owens Valley Millimeter Array. For this sample of 336 stars, we observe 3 mm emission above the 3 σ noise level toward 10 sources, six of which have also been detected optically in silhouette against the bright nebular background. In addition, we detect 20 objects in 3 mm continuum emission that do not correspond to known near-IR cluster members. Comparisons of our measured fluxes with longer wavelength observations enable rough separation of dust emission from thermal free-free emission, and we find substantial dust emission toward most objects. For the sample of 10 objects detected at both 3 mm and near-IR wavelengths, eight exhibit substantial dust emission. Excluding the two high-mass stars (θ1 Ori A and the BN object) and assuming a gas-to-dust ratio of 100, we estimate circumstellar masses ranging from 0.13 to 0.39 M☉. For the cluster members not detected at 3 mm, images of individual objects are stacked to constrain the mean 3 mm flux of the ensemble. The average flux is detected at the 3 σ confidence level and implies an average disk mass of 0.005 M☉, comparable to the minimum-mass solar nebula. The percentage of stars in Orion surrounded by disks more massive than ~0.1 M☉ is consistent with the disk mass distribution in Taurus, and we argue that massive disks in Orion do not appear to be truncated through close encounters with high-mass stars. Comparison of the average disk mass and number of massive dusty structures in Orion with similar surveys of the NGC 2024 and IC 348 clusters is used to constrain the evolutionary timescales of massive circumstellar disks in clustered environments.