Disks in close binary stars

Abstract

Context. Close binaries (abin ≤ 20 au) are known to harbor planets, yet planet formation is unlikely to succeed in such systems. Studying the dynamics of disks in close binaries can help to understand how those planets could have formed. Aims. We study the impact that numerical and physical parameters have on the dynamics of disks in close binaries. We use the γ-Cephei system as an example and focus on disk quantities such as disk eccentricity and the precession rate as indicators for the dynamical state of the disks. Methods. We simulate disks in close binaries by performing two-dimensional radiative hydrodynamical simulations using a modified version of the FARGO code. First, we perform a parameter study for different numerical parameters to confirm that our results are robust. In the second part, we study the effects of different masses and different viscosities on the disks’ dynamics. Results. Previous studies on radiative disks in close binaries used too low resolutions and too small simulation domains, which impacted the disk’s dynamics. We find that radiative disks in close binaries, after an initialization phase, become eccentric with mean eccentricities between 0.06 and 0.27 and display a slow retrograde precession with periods ranging from 4−40Tbin which depends quadratically on the disk’s mean aspect ratio. In general, the disks show a coherent, rigid precession which can be broken, however, by changes in the opacity law reducing the overall eccentricity of the disk.

The SPHERE view of multiple star formation

“…During the pericenter passage of the secondary star of eccentric binaries, strong spiral arms develop in the disk of both the primary and secondary star. This has been shown by hydrodynamical numerical simulations of close binary stars [91,[96][97][98][99][100][101] taking as test bench the γ Cep and α Cen systems. In Fig.…”

Planetesimal Drift in Eccentric Disks: Possible Outward Migration

“…For outward drift to be possible, depending on the temperature the eccentricity must be increasing outwards and 0.1. Simulations of disks in binary systems often find a region of the disk with these properties (e.g., Marzari et al 2009;Martin et al 2020;Jordan et al 2021), however the details vary substantially from one work to another. Jordan et al (2021) ran a series of two-dimensional radiative hydrodynamic simulations using the FARGO code.…”

“…Simulations of disks in binary systems often find a region of the disk with these properties (e.g., Marzari et al 2009;Martin et al 2020;Jordan et al 2021), however the details vary substantially from one work to another. Jordan et al (2021) ran a series of two-dimensional radiative hydrodynamic simulations using the FARGO code. They found that the eccentricity profile was dramatically affected by choices regarding the simulation domain, the boundary condition at the inner edge of the disk, the treatment of thermodynamics, and the numerical resolution.…”

Dust dynamics in planet-forming discs in binary systems

“…Later [97] and [98,99] argued that eccentricity was overestimated, and a proper treatment of viscous heating and radiative cooling, as well as the inclusion of disc self-gravity, implies lower disc eccentricities. However, most recently [100] showed that these works may have suffered from too low numerical resolution, and that more realistic viscosities lead to e ≈ 0.2, leaving this problem open.…”