The first stages of planet formation in binary systems: How far can dust coagulation proceed?

Abstract

We examine the first phase of the core accretion model, namely the dust growth/fragmentation in binary systems. In our model, a gas and dust disk is present around the primary star and is perturbed by the secondary. We study the effects of a secondary with/without eccentricity on the dust population to determine what sizes the aggregates can reach and how that compares to the dust population in disks around single stars. We find that the secondary star has two effects on the dust population. 1.) The disk is truncated due to the presence of the secondary star and the maximum mass of the particles is decreased in the lowered gas densities. This effect is dominant in the outer disk. 2.) The perturbation of the secondary pumps up the eccentricity of the gas disk, which in turn increases the relative velocity between the dust and the gas. Therefore the maximum particle sizes are further decreased. The second effect of the secondary influences the entire disk. Coagulation is efficiently reduced even at the very inner parts of the disk. The average mass of the particles is reduced by four orders of magnitude (as a consequence, the stopping time is reduced by one order of magnitude) in disks around binary systems compared to dust in disks around single stars.