The Clusters AgeS Experiment (CASE): The blue straggler Star M55-V60 caught amidst rapid mass exchange

TL;DR

This study analyzes the eclipsing blue straggler V60 in M55, revealing its physical parameters, confirming its cluster membership, and suggesting it is undergoing rapid conservative mass exchange, with a peculiar blue excess observed during primary eclipse.

Contribution

It provides detailed physical characterization of V60 and presents evidence of ongoing rapid mass exchange in a blue straggler within a globular cluster.

Findings

V60 is a member of M55 based on systemic velocity and proper motion.

The primary and secondary star parameters are precisely measured.

The system is undergoing rapid, conservative mass exchange.

Abstract

We analyze light and velocity curves of the eclipsing blue straggler V60 in the field of the globular cluster M55. We derive Mp=1.259+-0.025 Msun, Rp=1.102+-0.021 Rsun, Mbol,p=3.03+-0.09 mag for the primary and Ms=0.327+-0.017 Msun, Rs=1.480+-0.011 Rsun, Mbol,s=4.18+-0.12 mag for the secondary. We derive an apparent distance modulus (m-M)V=14.04_-0.09 mag. Based on the systemic velocity, distance, and proper motion of V60 we conclude that the system is a member of the cluster and argue that its present state is a result of rapid but conservative mass exchange which the binary is still undergoing. We report a peculiar blue excess on the ascending branch of the primary eclipse of V60 and discuss its possible origin.