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The Clusters AgeS Experiment (CASE): Variable Stars in the Globular Cluster M4

Kaluzny J., Thompson I. B., Rozyczka M., Krzeminski W.

Acta Astronomica

2013

Vol. 63, No. 2

181--201

Based on over 3000 BV images of M4 collected in years 1995-2009 we obtain light curves of 22 variables, 10 of which are newly detected objects. We identify four detached eclipsing binaries and eight contact binaries. Accurate periods are found for all but two variables. Nineteen variables are proper-motion members of the cluster, and the remaining three are field stars. Five variables are optical counterparts of X-ray sources. For one of the variables unassociated with X-ray sources we report a flare lasting for about 90 min and reaching an amplitude of ΔV=0.11 mag. One of the new contact binaries has a record-low mass ratio q=0.06. Another four such systems show season-to-season luminosity variations probably related to magnetic activity cycles, whose lengths are surprisingly similar to that of the solar cycle despite a huge difference in rotational periods. The location of contact binaries on the color-magnitude diagram of M4 strongly suggests that at least in globular clusters the principal factor enabling EW systems to form from close but detached binaries is stellar evolution. We identify 46 blue and yellow stragglers in M4 and discuss their properties. We also derive a map of the differential extinction in the central part of M4, and determine the reddening of a selected reference region, E(B-V)=0.392 mag.

A Proper Motion Study of the Globular Clusters M4, M12, M22, NGC 3201, NGC 6362 and NGC 6752

Zloczewski K., Kaluzny J., Rozyczka M., Krzeminski W., Mazur B., Thompson I. B.

Acta Astronomica

2012

Vol. 62, No. 4

357--375

We derive relative proper motions of stars in the fields of globular clusters M4, M12, M22, NGC 3201, NGC 6362 and NGC 6752 based on a uniform data set collected between 1997 and 2008. We assign a membership class for each star with a measured proper motion and show that these membership classes can be successfully used to eliminate field stars from color-magnitude diagrams of the clusters. They also allow for the efficient selection of rare objects such as blue/yellow/red stragglers and stars from the asymptotic giant branch. Tables with proper motions and photometry of over 87 000 stars are made publicly available via the Internet.