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The Clusters AgeS Experiment (CASE). Variable stars in the field of the globular cluster M12

J. Kałużny, W. Narloch, W. Pych, M. Różyczka (CAMK PAN Warsaw) and I.B. Thompson ( Carnegie Observatories) have been monitoring the field of the globular cluster M12 for 15 years in a search for variable stars. Thirty-six periodic or likely periodic variables have been identified; thirty-four of these are new detections. Among the latter there are 20 proper-motion members of the cluster: six detached or semi-detached eclipsing binaries, five contact binaries, five SX~Phe pulsators, and three yellow stragglers. Two of the eclipsing binaries are located in the turnoff region, one on the lower main sequence and the remaining three among the blue stragglers. Two contact systems are blue stragglers, and the remaining three reside in the turnoff region. In the blue straggler region is populated by 103 objects, of which 42 are proper motion members of M12, and another four are field stars. Forty-five of the remaining objects are located within two core radii from the center of the cluster, and as such they are likely genuine blue stragglers. Authors also report the discovery of the shortest period among contact systems in globular clusters in general, and of a radial color gradient of M12 (with the center of the cluster being bluer). Published paper.


Picture: Color-magnitude diagram for M12 with indicated locations of the discovered variables. Red, blue and black labels denote, respectively, cluster members, nonmembers and objects for which the membership data is missing or ambiguous. Copyright CAMK, AcA