Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...433..199l&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 433, no. 1, p. 199-215
Astronomy and Astrophysics
Astronomy
55
A Stars, B Stars, Infrared Astronomy, Infrared Imagery, Infrared Spectra, Near Infrared Radiation, Stellar Envelopes, Stellar Spectra, Astronomical Photometry, Astronomical Spectroscopy, Color-Color Diagram, Emission Spectra, Line Spectra, Pre-Main Sequence Stars
Scientific paper
Near-infrared (J, H, K) images were obtained for 16 Herbig Ae/Be stars. The primary goal was to determine the contributions by circumstellar nebulae and nearby sources to near-infrared photometry carried out with large beams. Quasi-simultaneous photometric results were obtained with small apertures. The emission toward five Herbig Ae/Be stars is extended, including all four Group II sources in our sample (Hillebrand et al. 1992); 13 objects have nearby sources (within 10 sec separation). However, the extended emission and nearby sources are too faint to affect previous photometry significantly. The surface brightness profiles of most of the nebulae can be explained by reflection nebulae which scatter the light from the central star/disk systems with single, isotropic scattering processes. The exception is Par 21, which may require emission from very small grains. The color-color diagram, making use of our new photometry, essentially agrees with the results of Lada & Adams (1992). The Group II objects in our sample tend to have extended emission more frequently than do Group I objects, supporting the suggestion of Hillebrand et al. that Group II sources are more affected by circumstellar envelopes. However, most of the near-infrared emission comes from the central (less than or = 6 sec) regions. This upper limit is still much larger than the expected size of accretion disks. Possible envelope effects could not be ruled out for most Herbig Ae/Be stars with unresolved emission. The images do not clearly favor very small, thermally emitting grains as the origin of the near-infrared emission. The problem still exists of how to explain the observed peaks near 3 sec in the spectral energy distributions of Herbig Ae/Be stars. The possible effects of envelopes and companions are addressed.
Colome Cecilia
Evans Neal J. II
Harvey Paul Michael
Li Wenbin
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