Relative velocities among accreting planetesimals in binary systems: The circumprimary case

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.01.022 Byline: P. Thebault (a)(b), F. Marzari (c), H. Scholl (d) Keywords: Planetary formation; Planetary dynamics; Accretion Abstract: We investigate classical planetesimal accretion in a binary star system of separation a.sub.ba[c]1/250AU by numerical simulations, with particular focus on the region at a distance of 1 AU from the primary. The planetesimals orbit the primary, are perturbed by the companion and are in addition subjected to a gas drag force. We concentrate on the problem of relative velocities [DELTA]v among planetesimals of different sizes. For various stellar mass ratios and binary orbital parameters we determine regions where [DELTA]v exceed planetesimal escape velocities v.sub.esc (thus preventing runaway accretion) or even the threshold velocity v.sub.ero for which erosion dominates accretion. Gaseous friction has two crucial effects on the velocity distribution: it damps secular perturbations by forcing periastron alignment of orbits, but at the same time the size-dependence of this orbital alignment induces a significant [DELTA]v increase between bodies of different sizes. This differential phasing effect proves very efficient and almost always increases [DELTA]v to values preventing runaway accretion, except in a narrow e.sub.ba0 domain. The erosion threshold [DELTA]vv.sub.ero is reached in a wide (a.sub.b,e.sub.b) space for small Author Affiliation: (a) Stockholm Observatory, Albanova Universitetcentrum, SE-10691 Stockholm, Sweden (b) Observatoire de Paris, Section de Meudon, F-92195 Meudon Principal Cedex, France (c) Dipartimento di Fisica, Universita di Padova, Via Marzolo 8, I-35131 Padova, Italy (d) Observatoire de la CA[acute accent]te d'Azur, Dept. Cassiopee, B.P. 4229, F-06304 Nice, France Article History: Received 25 July 2005; Revised 27 January 2006