GAS IN DUSTY DEBRIS DISKS

摘要

The presence of gas in dusty debris disks around main-sequence stars is reviewed. We present new observational results for the most prominent representative of the class, viz. the southern naked-eye star β Pictoris. The spatial and spectral distribution of observed atomic lines from the disk around the star is reproducable by a Keplerian rotation model to a high degree of accuracy. The expected velocity dispersion due to radiation pressure in resonance lines is not observed. Modeling the motion of different atomic species under the influence of gravity, radiation pressure and gas friction leads to the conclusion that an underlying decelerating component must be present in the disk. This braking agent is most likely hydrogen, with inferred average densities n_H > 10~6 cm~(-3). This could support the observational result of Thi et al. (2001) which indicated the presence of appreciable amounts of H_2 around the star β Pic.