Effects of dissipating gas drag onplanetesimal accretion in binary systems

摘要

We numerically investigate the conditions for planetesimal accretion in the circum-primary disk under the perturbing presence of a companion star, with focus on the γ Cepheisystem. Gas drag is included with a dissipating time scale of 10~5years. We show at the be-ginning(within 10~3~10~4years), gas drag damps the ΔV between planetesimals of same sizesand increases ΔV between planetesimals of different sizes. However, after increasing to highvalues(300~800m/s), we find the ΔV between bodies of different sizes decrease to very lowvalues (below 10m/s) in a few 10~5yrs(depending on the gas-dissipating time scale T_(dnmp),radialsize R_pand semi-major axis a_p of planetesimals). Hence, the high ΔV is somewhat short-lived,and runaway accretion can be turned on later. We conclude that the conditions for planetaryformation in binary systems (even close binary systems) are much better than what we expectedbefore.