Brightness variability in polar circumbinary disks

TL;DR

This paper investigates how brightness variations in polar circumbinary disks, caused by changing stellar illumination due to binary orbital motion, can reveal disk properties through observed flux changes.

Contribution

It introduces analytic and radiative transfer models to analyze brightness variability in misaligned polar disks, linking flux changes to disk geometry and structure.

Findings

Flux from the disk varies periodically over the binary orbit.

Brightness peaks twice per binary orbit due to illumination changes.

Flux variations can constrain disk geometry and vertical structure.

Abstract

In binary systems with a strongly misaligned disk, the central binary stars can travel a significant vertical distance above and below the disk's orbital plane. This can cause large changes in illumination of the disk over the course of the binary orbital period. We use both analytic and radiative transfer models to examine the effect of changes in stellar illumination on the appearance of the disk, particularly in the case of the polar disk HD 98800B. We find that the observed flux from the disk can vary significantly over the binary orbital period, producing a periodically varying lightcurve which peaks twice each binary orbit. The amount of flux variation is strongly influenced by the disk geometry. We suggest that these flux variations produce several observable signatures, and that these observables may provide constraints on different properties of the disk such as its vertical structure, geometry, and cooling rate.