On the potential origin of the circumbinary planet Delorme 1 (AB)b

TL;DR

This study explores possible formation scenarios for the circumbinary planet Delorme 1 (AB)b, analyzing in-situ formation, migration, and accretion processes to understand its current wide orbit and mass.

Contribution

The paper compares three formation models for Delorme 1 (AB)b using hydrodynamical simulations, highlighting their strengths and limitations in explaining the planet's observed properties.

Findings

Scenario I produces planets at the observed separation with realistic accretion rates but too high final mass.

Scenario II results in planets with observed accretion rates but masses above observations.

Scenario III matches the observed mass and accretion rate but predicts a smaller orbital separation.

Abstract

Many circumbinary gas giant planets have been recently discovered. The formation mechanism of circumbinary planets on wide orbits is unclear. We investigate the formation of Delorme 1 (AB)b, a 13$\pm$5M$_{\rm J}$ planet, orbiting its host binary at 84AU. The planet is accreting while having an estimated age of 40Myr, which is unexpected, as this process should have ceased due to the dissipation of the protoplanetary disc. Using the Smoothed Particle Hydrodynamics code SEREN, we model three formation scenarios for this planet. In Scenario I the planet forms in-situ on a wide orbit in a massive disc (by gravitational instability), in Scenario II closer to the binary in a massive disc (by gravitational instability), and in Scenario III much closer to the binary in a less massive disc (by core accretion). Planets in Scenario I stay at the observed separation, have mass accretion rates consistent with observed value, but their final mass is too high. In Scenario II, the planet reaches the observed separation through outward migration or scattering by the binary, and has mass accretion rate comparable to the observed; however, the planet mass is above the observed value. In Scenario III, the planet's final mass and mass accretion rate are comparable to the observed ones but the planet's separation is smaller. We conclude that all models may explain some features of the observations but not all of them, raising questions about how gas is accreted onto the planet from its circumplanetary disc, and of the presumed age of the system.