DUST-GAS INTERACTION IN PROTO-PLANETARY ACCRETION DISKS

摘要

The trajectories of dust particles in a proto-planetary nebula are calculated both analytically and numerically, as they undergo settling and radial infall due to gas drag. The analytical formulae are combined with a Boltzmann averaging procedure to obtain the evolutionary behaviour of a collection of particles of various sizes. It is found that a selective segregation process occurs in which all intermediate size particles (typically of the order of a centimeter at 1AU, and increasingly larger further out) very"quickly settle to the mid-plane, whereas smaller particles remain at all heights in the disk. The Boltzmann formalism is also used to derive the correct averaged equations of motion for a "fluid" composed of the dust grains; we deduce a typical particle size above which the standard fluid equation of motion fails to reproduce the behaviour of this collection of particles.