How cooling influences circumbinary discs

TL;DR

This study investigates how different cooling models affect the shape and structure of circumbinary discs, revealing that thermodynamics significantly influence cavity characteristics and disc precession.

Contribution

The paper introduces a parametrised $eta$ cooling model that effectively mimics radiative cooling effects in circumbinary disc simulations.

Findings

Cavity shape remains similar between radiative and locally isothermal models.

Inner disc structure varies slightly, affecting precession rates.

The $eta$-cooling model with $eta=1$ reproduces radiative model results.

Abstract

Circumbinary disc observations and simulations show large, eccentric inner cavities. Recent work has shown that the shape and size of these cavities depend on the aspect ratio and viscosity of the disc, as well as the binary eccentricity and mass ratio. It has been further shown that, for gaps created by planets, the cooling timescale significantly affects the shape and size of the gap. In this study, we consider the effect of different cooling models on the cavity shape in a circumbinary disc. We compare locally isothermal and radiatively cooled disc models to ones with a parametrised cooling timescale ($\beta$-cooling), implemented in 2D numerical simulations for varying binary eccentricities. While the shape of the cavity for radiative and locally isothermal models remains comparable, the inner disc structure changes slightly, leading to a change in the precession rate of the disc. With $\beta$-cooled models, the shape and size of the cavity changes dramatically towards values of $\beta$=1. Based on our findings, we introduce a parametrised $\beta$ model that accounts for the shorter cooling timescale inside the cavity while adequately reproducing the results of the radiative model, and we highlight that accurate treatment of the thermodynamics inside the cavity has a significant impact in modelling circumbinary systems.