A Search for Thermal Infrared Emission from Three Silhouette Disks in Orion
We report the detection of mid-infrared emission from the Orion Nebula silhouette circumstellar disk 218-354. We also observed the fields of the silhouette objects 183-405 and 121-1925 but did not detect either source. Our fluxes for 218-354 confirm the near-infrared excess detected by McCaughrean & O'Dell (1996), and the optical to mid-infrared spectral energy distribution is similar to that of T Tauri stars with moderately luminous disks. A reddened stellar continuum plus a standard circumstellar disk model with a dust luminosity of 2 L_sun fit the available data fairly well and implies that we are only detecting emission from the innermost regions of the large disk seen in silhouette. However, our data are fit slightly better by a single-temperature dust model, so the warmest dust may be distributed in a thin ring rather than a continuous disk, perhaps implying a gap in the disk beyond 0.4AU\@. Our upper limit for 183-405 shows that the mid-infrared luminosity of its disk is very weak relative its central star. In addition to the silhouette disk sources, our target fields also contain several other sources, four of which we detect in the mid-infrared. All of these sources show infrared excesses typical of circumstellar disks, supporting the suggestion that such disks are common in the Trapezium Cluster. The brightest such source, 180-403, has a very red spectral energy distribution and mid-infrared hydrocarbon features, and resembles the WL 16 protostar in the rho Ophiuchi dark cloud.
The Astronomical Journal
- Pub Date:
- January 1997