Dynamics and planet formation in/around binaries

TL;DR

This study investigates how binary star systems influence planetesimal accretion by analyzing encounter velocities and identifying conditions that either promote or hinder planet formation, considering gas effects and binary parameters.

Contribution

It provides a comprehensive numerical analysis of encounter velocity distributions in binary systems, revealing distinct accretion regimes and their dependence on binary configurations.

Findings

Classical accretion occurs where encounter velocities are low.

High encounter velocities above erosion threshold prevent accretion.

Intermediate velocities allow slower planetesimal growth, possibly via type II runaway.

Abstract

We study to which extent planetesimal accretion is affected by the perturbing presence of a compagnon star. We concentrate on one crucial parameter: the distribution of encounter velocities within the planetesimal swarm. We numerically explore the evolution of this parameter taking into account the secular perturbations of the binary and friction due to the very likely presence of gas in the disk. $<\Delta v>$ maps are derived, for planetesimals of different sizes, for a total of 120 binary configurations (eccentricity eb and separation ab). We identify for each case 3 different accreting behaviours. 1) In regions where no significant dV increase is observed, ``classical'' (i.e., single-star) accretion is possible. 2) In regions where $dV>v_{ero}$, the threshold velocity above which all impacts are eroding, no accretion is possible and planet growth is stopped. 3) In between these 2 limiting behaviours, a large fraction of binary configurations leads to significant dV increase, but still below the erosion threshold. In this intermediate case, planetesimal growth can occur, but proceeds slower than in the single-star case, possibly following the so-called type II runaway groth mode.