The evolutionary status of W Ursae Majoris-type systems

TL;DR

This study analyzes physical parameters of 130 W UMa systems to understand their evolutionary status, revealing no difference between types and highlighting the roles of energy transfer, angular momentum loss, and mass loss in their evolution.

Contribution

It provides a comprehensive analysis of W UMa systems' evolutionary status using a large dataset, emphasizing the effects of energy transfer, angular momentum loss, and mass loss.

Findings

No evolutionary difference between W- and A-type systems in M-J diagram.

Energy transfer causes thermal relaxation oscillation in W UMa systems.

Mass ratio decreases with total mass due to angular momentum and mass loss.

Abstract

Well-determined physical parameters of 130 W UMa systems have been collected from the literature. Based on these data, the evolutionary status and dynamical evolution of W UMa systems are investigated. It is found that there is no evolutionary difference between W- and A-type systems in $M-J$ diagram which is consistent with the results derived from the analysis of observed spectral type, $M-R$ and $M-L$ diagrams of W UMa systems. $M-R$ and $M-L$ diagrams of W- and A-type systems indicate that a large amount of energy should be transferred from the more massive to the less massive component so that they are not in thermal equilibrium and undergo thermal relaxation oscillation (TRO). Meanwhile, the distribution of angular momentum, together with the distribution of mass ratio, suggests that the mass ratio of the observed W UMa systems is decreased with the decrease of their total mass. This could be the result of the dynamical evolution of W UMa systems which suffer angular momentum loss (AML) and mass loss due to magnetic stellar wind (MSW). Consequently, the tidal instability forces these systems towards the lower q values and finally to fast rotating single stars.