Long-term Photometric Analysis of the Active W UMa-type System TU Bootis

TL;DR

This study analyzes long-term photometric data of the W UMa-type binary TU Boo, revealing rapid mass transfer, period changes, and evolutionary insights into the system's history and component characteristics.

Contribution

It provides the first multi-epoch light curve analysis of TU Boo, linking period variations to mass transfer and evolutionary processes in contact binaries.

Findings

Detected correlated changes in secondary star size and period anomalies.

Supported rapid, large-scale mass transfer between components.

Suggested a past mass ratio reversal and advanced evolutionary state.

Abstract

We present multi-color light curves for the W UMa-type eclipsing binary TU Boo for two epochs separated by 22 years. An analysis of the O-C diagram indicates the earlier observations took place right in the middle of a major period change, thus allowing for a unique study on mass transfer and period changes in this W UMa-type system. We compute model fits to our light curves, along with the only other published set, using the Wilson-Devinney program, and find temporally correlated changes in the size of the secondary component with anomalies in the O-C diagram. We investigate the cause of these changes and find support for the existence of rapid, large-scale mass transfer between the components. We postulate that this interaction allows them to maintain nearly equal surface temperatures despite having achieved only marginal contact. We also find support for the evolutionary scenario in which TU Boo has undergone a mass ratio reversal in the past due to large-scale mass transfer so that what is presently the secondary component of TU Boo is in an advanced evolutionary state, oversized due to a helium-enriched core, with a total system age of $\geq$ 10 Gyr.