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Session 47 - Circumstellar Disks & Shells.
Display session, Thursday, January 08
Exhibit Hall,
This poster presents H (1.4--1.8\mum) and K (2.1--2.4\mum) spectra taken with GRIM II (R=400) at the Apache Point Observatory of a sample of Herbig Ae/Be stars, the intermediate mass pre-main sequence stars. There is considerable controversy over the amount and rate of accretion occuring in these systems, and the geometry of their circumstellar matter (disks, envelopes, both?). Upper level Hydrogen recombination lines provide a little-used method for investigating the density conditions in the immediate vicinity of these stars. The most prominent features in many of the near-infrared spectra are the Brackett emission series, seen from Br\gamma to \simBr17, with widely varying strengths between stars. In those cases where the emission is strong, the Br10/Br\gamma ratio is significantly higher than 0.3, the Case B value, a result also seen by Harvey (1984 PASP, 96, 297) and Nisini et al. (1995 Aamp;A, 302, 169). This is expected when the gas density in the emitting region is 10^10 to 10^12 cm^-3 or greater (Randich et al. 1991 Aamp;AS, 88, 31). We use the Brackett decrement-- the line strengths as a function of upper level n-- as a diagnostic for the density in the hot, circumstellar environment where these lines originate. In addition, we present 7.5--13.5 \mum HIFOGS spectra of these stars which probes the cooler circumstellar material further from the stellar surface. Correlations with other stellar properties, such as spectral type, photometric variability, infrared excess, and optical spectral features, are also explored. Finally, the presence or absence of other near infrared lines of interest, including HeI, [FeII] and H_2 are briefly discussed.
