CURiuos Variables Experiment (CURVE): Variable Stars in the metal-poor Globular Cluster M56

TL;DR

This study surveyed the globular cluster M56 to identify variable stars, discovering seven variables including a new RR Lyrae star and analyzing period changes in an RV Tauri variable, contributing to understanding stellar evolution.

Contribution

The paper reports the discovery of new variable stars in M56, including the third RR Lyrae, and provides analysis of period changes in an RV Tauri star, enhancing knowledge of variable star behavior in metal-poor clusters.

Findings

Seven variable stars detected, including two new identifications.

The third RR Lyrae star identified in M56.

Period change observed in RV Tauri star V6, suggesting complex stellar evolution.

Abstract

We have surveyed a 6.5' x 6.5' field centered on the globular cluster M56 (NGC 6779) in search for variable stars. We have detected seven variables, among which two objects are new identifications. One of the new variables is an RR Lyrae star, the third such star in M56. Comparison of the new observations and old photometric data for an RV Tauri variable V6 indicates a likely period change in the star. Its slow and negative rate of -0.005+/-0.003 d/yr would disagree with post-AGB evolution, however this could be a result of blue-loop evolution and/or random fluctuations of the period.