Circumbinary discs: Numerical and physical behaviour

Abstract

Aims. Disks around a central binary system play an important role in star and planet formation as well as for the evolution of galactic disks. These circumbinary disks are strongly disturbed by the time varying potential of the binary system and display a complex dynamical evolution that is not well understood. Our goal is to investigate the impact of disk and binary parameters to the dynamical aspects of the disk. Methods. We study the evolution of circumbinary disks under the gravitational influence of the binary using two-dimensional hydrodynamical simulations. To distinguish between physical and numerical effects we apply three hydrodynamical codes. First we analyse in detail numerical issues concerning the conditions at the boundaries and grid resolution. We then perform a series of simulations with different binary (eccentricity, mass ratio) and disk parameters (viscosity, aspect ratio) starting from a reference model with Kepler-16 parameter.Results. Concerning the numerical aspects we find that the inner grid radius must be of the order of the binary semi-major axis, with free outflow conditions applied such that mass can flow onto the central binary. A closed inner boundary leads to unstable evolutions. We find that the inner disk turns eccentric and precesses for all investigated physical parameters. The precession rate is slow with periods (T prec ) starting at around 500 binary orbits (T bin ) for high viscosity and large H/R where the inner hole is smaller and more circular. Reducing α and H/R increases the gap size and T prec reaches 2500 T bin . For varying binary mass ratios q bin the gap size remains constant whereas T prec decreases for increasing q bin . For varying binary eccentricities e bin we find two separate branches in the gap size and eccentricity diagram. The bifurcation occurs at around e crit ≈ 0.18 where the gap is smallest with the shortest T prec . For e bin smaller and larger than e crit the gap size and T prec increase. Circular binaries create the most eccentric disks.

Double-peaked [O i] Profile: A Likely Signature of the Gaseous Ring around KH 15D

“…Mundt et al (2010) claim that there is a slight blue asymmetry (14%) in the [O I] λ6300 line profiles. For a system like the KH 15D with a close binary, the [O I] emitting regions can be disturbed by the time varying potential of the binary system (Thun et al 2017), causing some variability and asymmetry in the [O I] λ6300 line profile as proposed by Mundt et al (2010). However, as discussed in Sect.…”

Signatures of an eccentric disc cavity: Dust and gas in IRS 48

“…Other works investigate the evolution of circumbinary discs over much longer timescales (e.g. Miranda et al 2017;Thun et al 2017), however these tend to be done with two dimensional simulations which are cheaper.…”

1:1 orbital resonance of circumbinary planets

“…To model discs around binary stars, we perform viscous hydrodynamic simulations of thin discs in two dimensions (2D) using a modified version of the PLUTO-code (Mignone et al 2007) that allows for computation on graphics processing units (Thun et al 2017). We use a locally isothermal disc because the final equilibrium structure of circumbinary discs with full radiative cooling and viscous heating is similar to a locally isothermal model using the equilibrium tem- Table 1: Parameters for Kepler-413 and -47, as used in the simulations.…”