Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........8r&link_type=abstract
Ph.D. Thesis Hawaii Univ., Honolulu.
Astronomy and Astrophysics
Astronomy
2
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
Scientific paper
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; however, the models often underpredict the near-infrared (NW, 1-5 micrometers) 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 micrometer 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 singlebeam SEDs. While resolved, an isotropic 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 micrometers and thus will not explain excesses in the 3-5 micrometer 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 percent 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.
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