Formation and Evolution of W UMa Stars: Fallacies and Corrections

TL;DR

This paper critically examines the formation and evolution of W UMa stars, emphasizing the importance of observational biases, physical parameters, and multiple evolutionary processes in understanding their life cycle.

Contribution

It offers corrections to previous interpretations of period histograms and presents a comprehensive view of the factors influencing W UMa star evolution.

Findings

Period histograms are affected by selection effects and spatial distribution.

The age of W UMa binaries can be up to several Gyr depending on initial conditions.

The mean contact stage lifetime is approximately 1.6 Gyr.

Abstract

The period histograms of eclipsing binaries generated with ASAS data cannot only be interpreted by orbital evolution. The eclipse probabilities, selection effects and space distributions in the solar neighborhood should be considered before any interpretations are made. Depending upon physical dimensions (total mass and period) of the progenitor stars and the efficiency of angular momentum loss (AML) mechanism, a newly formed W UMa type binary can be at any age up to several Gyr, and evolution in the contact stage is controlled not only by angular momentum and mass loss but also by mass transfer between the component stars. Thus, mean life of contact stages should be about 1.6 Gyr. A different time scale would cause inconsistencies.