Disc-protoplanet interaction

Influence of circumprimary radiative discs on self-gravitating protoplanetary bodies in binary star systems

¹ Institute for Astrophysics (IfA), University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
e-mail: markus.gyergyovits@univie.ac.at
² IMCCE – Observatoire de Paris, 77 avenue Denfert-Rochereau, 75014 Paris, France
³ Planetarium Mannheim, Wilhelm-Varnholt-Allee 1, 68165 Mannheim, Germany
⁴ Department of Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria

Received: 7 May 2013
Accepted: 5 May 2014

Abstract

Context. More than 60 planets have been discovered so far in systems that harbour two stars, some of which have binary semi-major axes as small as 20 au. It is well known that the formation of planets in such systems is strongly influenced by the stellar components, since the protoplanetary disc and the particles within are exposed to the gravitational influence of the binary. However, the question on how self-gravitating protoplanetary bodies affect the evolution of a radiative, circumprimary disc is still open.

Aims. We present our 2D hydrodynamical GPU-CPU code and study the interaction of several thousands of self-gravitating particles with a viscous and radiative circumprimary disc within a binary star system. To our knowledge this program is the only one at the moment that is capable to handle this many particles and to calculate their influence on each other and on the disc.

Methods. We performed hydrodynamical simulations of a circumstellar disc assuming the binary system to be coplanar. Our grid-based staggered mesh code relies on ideas from ZEUS-2D, where we implemented the FARGO algorithm and an additional energy equation for the radiative cooling according to opacity tables. To treat particle motion we used a parallelised version of the precise Bulirsch – Stoer algorithm. Four models in total where computed taking into account (i) only N-body interaction; (ii) N-body and disc interaction; (iii) the influence of computational parameters (especially smoothing) on N-body interaction; and (iv) the influence of a quiet low-eccentricity disc while running model (ii). The impact velocities were measured at two different time intervals and were compared.

Results. We show that the combination of disc- and N-body self-gravity can have a significant influence on the orbit evolution of roughly Moon sized protoplanets.

Conclusions. Not only gas drag can alter the orbit of particles, but the gravitational influence of the disc can accomplish this as well. The results depend strongly on the state of the disc (i.e. quiet or dynamically evolving) – according to encounter-probability distributions, planet formation can be strongly altered if there is a dynamically evolving gas disc – and also on the smoothing parameter.