Does the mass distribution in discs influence encounter-induced losses in young star clusters?

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: mstein@mpifr.de

Received: 25 November 2013
Accepted: 5 March 2014

Abstract

Context. One mechanism for the external destruction of protoplanetary discs in young dense clusters is tidal disruption during the flyby of another cluster member. The degree of mass loss in such an encounter depends, among other parameters, on the distribution of the material within the disc. Previous work showed that this is especially so in encounters that truncate large parts of the outer disc. The expectation is that the number of completely destroyed discs in a cluster also depends on the mass distribution within the discs.

Aims. Here we test this hypothesis by determining the influence of encounters on the disc fraction and average disc mass in clusters of various stellar densities for different mass distributions in the discs.

Methods. This is done by performing nbody6simulations of a variety of cluster environments, where we track the encounter dynamics and determine the mass loss due to these encounters for different disc-mass distributions.

Results. We find that although the disc-mass distribution has a significant impact on the disc losses for specific star-disc encounters, the overall disc frequency generally remains unaffected. The reason is that in single encounters the dependence on the mass distribution is strongest if both stars have very different masses. Such encounters are rather infrequent in sparse clusters. In dense clusters these encounters are more common; however, here the disc frequency is largely determined by encounters between low-mass stars such that the overall disc frequency does not change significantly.

Conclusions. For tidal disruption the disc destruction in clusters is fairly independent of the actual distribution of the material in the disc. The all determining factor remains the cluster density.