NEAR-INFRARED (J, H, K) IMAGING OF HERBIG AE BE STARS/

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 wi th large beams. Quasi-simultaneous photometric results were obtained w ith small apertures. The emission toward five Herbig Ae/Be stars is ex tended, including all four Group II sources in our sample (Hillenbrand et al. 1992); 13 objects have nearby sources (within 10'' separation) . However, the extended emission and nearby sources are too faint to a ffect previous photometry significantly. The surface brightness profil es of most of the nebulae can be explained by reflection nebulae which scatter the light from the central star/disk systems with single, iso tropic scattering processes. The exception is Par 21, which may requir e 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 sugg estion of Hillenbrand et al. that Group II sources are more affected b y circumstellar envelopes. However, most of the near-infrared emission comes from the central (less-than-or-equal-to 6'') regions. This uppe r 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 ver y small, thermally emitting grains as the origin of the near-infrared emission. The problem still exists of how to explain the observed peak s near 3 mum in the spectral energy distributions of Herbig Ae/Be star s. The possible effects of envelopes and companions are addressed.