1-5 Micron Imaging of Deeply Embedded Young Stellar Objects
Abstract
Spectral energy distributions (SEDs) are one of the primary tools for analyzing the natures of young stellar objects. Theoretical models of SEDs have achieved some success over a wide frequency range (e.g., Adams et al. 1987, ApJ 312, 788); however, the models often underpredict the near-infrared (NW, 1-5 μm) fluxes observed with single-element photometers by more than an order of magnitude. This observed "extra" flux is generally thought to be radiation which is scattered into the observer's beam from anisotropically distributed material surrounding the protostar. I explore a sample of well-known protostars with a seeing-matched InSb photodiode array camera; fourteen objects have been imaged in the J through M broadband filters, and many of these were imaged through a circular variable filter scanned through the 3.08 μm water ice band or through a linear polarizer with the K filter. These images are used to separate the scattered light from the line-of-sight radiation which together make up the published single-beam SEDs. While resolved, anisotropic scattering accounts for the NIR excesses in some objects, the general scenario is somewhat more complex. For instance, scattering from circumstellar material is seldom significant at wavelengths greater than 3 μm and thus will not explain excesses in the 3-5 μm region. Some objects appear completely point-like, yet have significant NIR excesses, implying that either scattering is significant on very small scales or that other processes are involved. The implications of these findings concerning models of YSOs and their SEDs are discussed. In addition, we find that approximately 40% of these objects (and of a larger sample) appear to be multiple, in rough agreement with the apparent frequency for Main Sequence stars. Finally, five of the fourteen objects appear to have varied significantly in intensity over periods ranging from months to years. We suggest several possible mechanisms for variations on these time scales.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- December 1992
- Bibcode:
- 1992PhDT.........8R
- Keywords:
-
- SPECTRAL ENERGY DISTRIBUTIONS;
- Physics: Astronomy and Astrophysics;
- Imaging Techniques;
- Infrared Astronomy;
- Infrared Imagery;
- Near Infrared Radiation;
- Protostars;
- Radiant Flux Density;
- Spectral Energy Distribution;
- Image Filters;
- Light Scattering;
- Line Of Sight;
- Mathematical Models;
- Polarizers;
- Stellar Evolution;
- Astronomy