How bright are the gaps in circumbinary disk systems?

TL;DR

This paper uses 3D MHD simulations to quantify the luminosity of streams passing through gaps in circumbinary disks, finding they are faint and do not significantly affect the expected dark gaps.

Contribution

It provides the first detailed luminosity estimates of streams in circumbinary disks, showing they are weak and minimally impact the thermal gap signature.

Findings

Streams have luminosity only a few percent of surrounding disk regions.

Luminosity mainly from weak laminar shocks.

Streams do not significantly alter the predicted dark gaps.

Abstract

When a circumbinary disk surrounds a binary whose secondary's mass is at least $\sim 10^{-2}\times$ the primary's mass, a nearly empty cavity with radius a few times the binary separation is carved out of the disk. Narrow streams of material pass from the inner edge of the circumbinary disk into the domain of the binary itself, where they eventually join onto the small disks orbiting the members of the binary. Using data from 3-d MHD simulations of this process, we determine the luminosity of these streams; it is mostly due to weak laminar shocks, and is in general only a few percent of the luminosity of adjacent regions of either the circumbinary disk or the "mini-disks". This luminosity therefore hardly affects the deficit in the thermal continuum predicted on the basis of a perfectly dark gap region.