On the energy dissipation rate at the inner edge of circumbinary discs

TL;DR

This paper investigates how energy is dissipated at the inner edge of circumbinary discs through simulations, revealing the mechanisms and implications for observed spectral energy distributions in tight PMS binaries.

Contribution

It provides a detailed analysis of energy dissipation mechanisms at the inner edge of circumbinary discs, including the role of shocks and viscous friction, and links these to observable spectral features.

Findings

Energy dissipation at the disc edge is linked to tidal torques and shocks.

The dissipation rate is proportional to the potential energy and accretion rate.

Inner edge emission dominates the SED at 1-10 μm for tight PMS binaries.

Abstract

We study, by means of numerical simulations and analysis, the details of the accretion process from a disc onto a binary system. We show that energy is dissipated at the edge of a circumbinary disc and this is associated with the tidal torque that maintains the cavity: angular momentum is transferred from the binary to the disc through the action of compressional shocks and viscous friction. These shocks can be viewed as being produced by fluid elements which drift into the cavity and, before being accreted, are accelerated onto trajectories that send them back to impact the disc. The rate of energy dissipation is approximately equal to the product of potential energy per unit mass at the disc's inner edge and the accretion rate, estimated from the disc parameters just beyond the cavity edge, that would occur without the binary. For very thin discs, the actual accretion rate onto the binary may be significantly less. We calculate the energy emitted by a circumbinary disc taking into account energy dissipation at the inner edge and also irradiation arising there from reprocessing of light from the stars. We find that, for tight PMS binaries, the SED is dominated by emission from the inner edge at wavelengths between 1-4 and 10 $\mu$m. This may apply to systems like CoRoT 223992193 and V1481 Ori.