Planetary migration in wind-fed non-stationary accretion disks in binary systems

¹ Dr. Remeis-Sternwarte & ECAP, Univ. Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
² Sternberg Astronomical Institute, Lomonosov Moscow State University, Universitetsky prospekt 13, 119234 Moscow, Russia

^★ Corresponding author; alex.nekrasov@fau.de

Received: 26 April 2024
Accepted: 11 December 2024

Abstract

Context. An accretion disk can be formed around a secondary star in a binary system when the primary companion leaves the main sequence and starts to lose mass at an enhanced rate.

Aims. We study the accretion disk evolution and planetary migration in wide binaries.

Methods. We used a numerical model of a non-stationary alpha disk with a variable mass inflow. We took into account that the low- mass disk has an extended region that is optically thin along the rotation axis. We considered irradiation by both the host star and the donor. The migration path of a planet in such a disk is determined by the migration rate varying during the disk evolution.

Results. Giant planets may open and close the density gap several times over the disk lifetime. We identify a new type of migration specific to parts of the growing disk with a considerable radial gradient of an aspect ratio. Its rate is enclosed between the type II and the fast type I migration rates determined by the ratio of time and radial derivatives of the disk aspect ratio. Rapid growth of the wind rate just before the envelope loss by the donor leads to the formation of a zone of decretion, which may lead to substantial outward migration. In binaries with an initial separation of a ≲ 100 AU, migration becomes most efficient for planets with 60–80 Earth masses. This results in approaching the distance from the host star, where the tidal forces become non-negligible. Less massive Neptune-like planets at the initial orbits r_p ≲ 2 AU can reach these internal parts in binaries with a ≲ 30 AU.

Conclusions. In binaries, mass loss by the primary component at late evolutionary stages can significantly modify the structure of a planetary system around the secondary component, resulting in mergers of relatively massive planets with a host star.