Disk Evolution in Young Binaries: from Observations to Theory

TL;DR

This paper reviews observational evidence and theoretical models of disk evolution in young binary star systems, highlighting how binary parameters influence disk properties and planet formation potential.

Contribution

It provides a comprehensive synthesis of observational diagnostics, analyzes correlations within binaries, and discusses models of disk evolution including isolated and circumbinary reservoirs.

Findings

Inner disk properties show varying degrees of correlation depending on binary separation and mass ratio.

Evidence suggests both isolated and circumbinary disk models are relevant for explaining observations.

Disks in binary systems have different lifetimes, affecting planet formation potential.

Abstract

The formation of a binary system surrounded by disks is the most common outcome of stellar formation. Hence studying and understanding the formation and the evolution of binary systems and associated disks is a cornerstone of star formation science. Moreover, since the components within binary systems are coeval and the sizes of their disks are fixed by the tidal truncation of their companion, binary systems provide an ideal "laboratory" in which to study disk evolution under well defined boundary conditions. In this paper, we review observations of several inner disk diagnostics in multiple systems, including hydrogen emission lines (indicative of ongoing accretion), $K-L$ and $K-N$ color excesses (evidence of warm inner disks), and polarization (indicative of the relative orientations of the disks around each component). We examine to what degree these properties are correlated within binary systems and how this degree of correlation depends on parameters such as separation and binary mass ratio. These findings will be interpreted both in terms of models that treat each disk as an isolated reservoir and those in which the disks are subject to re-supply from some form of circumbinary reservoir, the observational evidence for which we will also critically review. The planet forming potential of multiple star systems is discussed in terms of the relative lifetimes of disks around single stars, binary primaries and binary secondaries. Finally, we summarize several potentially revealing observational problems and future projects that could provide further insight into disk evolution in the coming decade