Observations of massive contact binaries in the local universe

TL;DR

This paper reviews the current observational understanding of massive contact binary stars, discussing detection methods, statistical insights, challenges, and future prospects in studying their evolution and role in producing exotic astrophysical objects.

Contribution

It provides a comprehensive overview of observational techniques, known systems, and the challenges faced in characterizing massive contact binaries, highlighting future research directions.

Findings

Sample of confirmed systems and their statistical properties

Identification of biases and limitations in current methods

Discussion of future observational strategies

Abstract

The contact phase represents a crossroad in the evolution of massive binary stars. Depending on the internal physics, the predicted end products can vary greatly including various exotic objects such as Be stars, magnetic massive stars, LBVs and gravitational wave sources. This phase also offers a unique observational laboratory to study binary interaction physics. Here, I review the current state of the field of massive contact binary observations. I summarize the techniques available to identify and characterize these systems as well as the limitations of each and the potential biases that they introduce. I present the sample of known confirmed systems and what the bulk statistics can tell us about their formation and evolution. Next I discuss the challenges that these systems pose from a characterization point of view and how we can overcome these. Finally I discuss the future direction of the field on the observational side.