Circumbinary discs with radiative cooling and embedded planets

Abstract

Context. As of today ten circumbinary planets orbiting solar type main sequence stars have been discovered. Nearly all of them orbit around the central binary very closely to the region of instability where it is difficult to form them in situ. Hence, it is assumed that they formed further out and migrated to their observed position, which will be determined by binary, disc and planet properties. Aims. We extend previous studies to a more realistic thermal disc structure and determine what parameter influence the final parking location of a planet around a binary star. Methods. We perform two-dimensional numerical simulations of viscous accretion discs around a central binary that include viscous heating and radiative cooling from the disc surfaces. We vary the binary eccentricity as well as disc viscosity and mass. Results. Concerning the disc evolution we find that it can take well over 100 000 binary orbits until an equilibrium state is reached. As seen previously, we find that the central cavity opened by the binary becomes eccentric and precesses slowly in a prograde sense. Embedded planets migrate to the inner edge of the disc. In cases of lower disc viscosity they migrate further in maintaining a circular orbit, while for high viscosity they are parked further out on an eccentric orbit. Conclusions. Discs around binary stars are eccentric and precess very slowly around the binary. The final location of an embedded planet is linked to its ability to open a gap in the disc. Gap opening planets separate inner from outer disc, preventing eccentricity excitation in the latter and making it more circular. This allows embedded planets to migrate closer to the binary, in agreement with the observations. The necessary condition for gap opening and the final planet position depend on the planet mass and disc viscosity. A&A proofs: manuscript no. cb_cooling Kepler M A M B q bin a bin e bin T bin [M ] [M ] [au] [d] 16 0.67 0.20 0.29 0.22 0.16 41.0 38 0.95 0.25 0.26 0.15 0.10 18.8

Circumbinary planets -- the next steps

“…There is an over-abundance of planets orbiting near the dynamical stability limit. This is likely the result of migratory formation of the planets, stalling near the edge of an inner disc cavity, which roughly coincides with the dynamical stability limit (Holman & Wiegert, 1999;Kley et al, 2019). Whilst this is not the sole result of an observational bias ( Fig.…”

Circumbinary Accretion from Finite and Infinite Disks

“…We acknowledge, nevertheless, that Moody et al (2019) focused on the q b = 1 case; thus, the qualitative consistency between 2D and 3D remains untested for q b = 1. The equation of state (EoS) assumed could have a moderate effect on our results by modifying the angular momentum currents (Lee 2016;Miranda & Rafikov 2019), although it is unclear whether a more realistic EoS (see, e.g., Kley et al 2019) would make l 0 larger or smaller. Additional physics, such as the launching of a magnetized winds (e.g., Blandford & Payne 1982), could modify the angular momentum transfer rate.…”

Gap, shadows, spirals, and streamers: SPHERE observations of binary-disk interactions in GG Tauri A

“…The computational time needed to reach the actual disk structure from the initial power-law profile can be long (Kley et al 2019). To ensure a feasible time step for the grid code, we did not include the stars themselves in the simulation domain, but the inner grid boundary was set to a radius of 1 a bin (35 au) and we added the binary as n-bodies inside the domain to create the potential, using a gravitational softening parameter of 0.6 (see Kley et al 2019). As discussed in Kley et al (2019), such an inner boundary does not change the dynamics of the circumbinary disk or gap width.…”