COLLISIONAL VAPORIZATION OF DUST AND PRODUCTION OF GAS IN THE β PICTORIS DUST DISK

摘要

The need for replenishment of the stable gas observed in the β Pictoris system raises a question about the origin of the gas. Correlations between the gas and the dust distribution suggest that the source is related to the dust. Spec-troscopic observations imply that the gas is rotating at Keplerian velocity: this includes also the species that, in absence of braking, would be accelerated away from the star by the radiation pressure. We examine the possibility that the gas originates from collisional vaporization of the dust in the disk and the consequences for the gas velocity distribution and the line profiles of spectral features generated by the gas. A simple model of dust distribution and a model of individual dust-dust collision are used to calculate the gas production rate in the disk. Comparing with the gas column densities derived from observations, the escape times of the atoms from the disk are estimated. For the dust distribution and collision model considered, the vaporization of dust leads to the gas production rates of the order between 0.5 x 10~(12) and 2 x 10~(13) g s~(-1) for the grains with the collisional properties close to those of silicate and ice, respectively. We point out the uncertainties in the collision models. We also found that, for the lines of sight bypassing the star, velocity distributions of gas particles released from orbiting bodies can show a peak at Keplerian velocity even in the absence of braking, despite large acceleration by radiation pressure.