How cooling influences circumbinary discs

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.

Automated summary

Observations and simulations of circumbinary discs have shown the presence of large eccentric inner cavities. The shape and size of these cavities depend on various factors, including disc properties, binary properties, and cooling timescale. This study investigates the effect of different cooling models on the cavity shape, comparing locally isothermal and radiatively cooled disc models to a parametrised cooling timescale model. The results show that the cavity shape remains comparable for radiative and isothermal models, but changes dramatically for the parametrised cooling model. A new parametrised beta model is introduced to accurately reproduce the results of the radiative model and highlight the importance of accurately modeling the thermodynamics inside the cavity in circumbinary systems.