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How to Cite

The Globular Cluster M69: Color-Magnitude Diagram and Variable Stars. (2006). Revista Mexicana De Astrofísica Y Astronomía Serie De Conferencias, 26, 168. https://doi.org/10.22201/ia.14052059p.2006.26.108

Abstract

We present BV photometry and the results of a search for stellar variability in the globular cluster M69 (NGC 6637). The images were collected over a one-week run at the Warsaw 1.3-m telescope in Las Campanas Observatory in April 2003. The photometry was performed using DAOPHOT II/ALLFRAME and the variable stars search was made with ISIS 2.2. Our color-magnitude diagram (CMD) shows a red horizontal branch (HB) typical of moderately, metal-rich clusters as M69, with significant contamination by field stars. We are unable to confirm or discard the possible blue HB extension suggested by other authors. In our search for variable stars we found 61 candidates, 53 of which are new discoveries. Among these 53 newly discovered variable stars we have 8 RR Lyrae, 4 SX Phe, 10 eclipsing variable and 15 LPV candidates. In the case of RR Lyrae stars, cluster membership is still uncertain since the ALLFRAME magnitudes do not place these stars at the HB level, as would have been expected in the case they were bona-fide cluster members.