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K. Nielson, S. Terebey (California State Univeristy, Los Angeles), D. Van Buren (Jet Propulsion Laboratory)
The class I protostar TMC-1 (IRAS 04381+2540) located in the Taurus star-forming region is oriented favorably for determining the properties of the circumstellar envelope. Using a Monte Carlo scattering code, we generate a library of models which is then compared to Hubble Space Telescope NICMOS images at 1.6 microns of TMC-1 and matched based on an angular intensity profile. We find that our models are capable of fitting the observed profile well, with accurate limb brightening and apparent cavity width. The main differences are a lack of observed emission from the rear of the outflow cavity, as well as a slight asymmetry not accounted for in the models.
Previous work shows that the extended nebulosity seen around protostars at near-infrared wavelengths can be explained by stellar photons that scatter off circumstellar dust. Model density distributions typically require several components to fit the data: a thin opaque disk, a circumstellar envelope ("infall envelope") and an "empty" outflow cavity. The results of this model fitting suggest that TMC-1 is inclined at about 50-60 degrees and has a cavity opening of 80-90 degrees. To explain the relative lack of scattered emission from the rear wall of the outflow cavity requires the dust to be very highly forward scattering. This in turn suggests larger than expected dust grains whose sizes are comparable to the 1.6 micron observation wavelength.
The author(s) of this abstract have provided an email address for comments about the abstract: nielson@caltech.edu
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.