The Clusters AgeS Experiment (CASE): Variable Stars in the Globular Cluster M4
Kaluzny, J.; Thompson, I. B.; Rozyczka, M.; Krzeminski, W.
Abstract:
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.

DOWNLOADS:
The paper (PDF) "CCD Photometry of Faint Variable Stars in the Field of the Globular Cluster M4"
Kaluzny, Janusz; Thompson, Ian B.; Krzeminski, Wojtek;
1997, Astronomical Journal v.113, p. 2219-2225
The paper (PDF) "Clusters Ages Experiment: Hot Subdwarfs and Luminous White Dwarf Candidates in the Field of the Globular Cluster M4"
Mochejska, B. J.; Kaluzny, J.; Thompson, I.; Pych, W.;
2002, The Astronomical Journal, Volume 124, Issue 3, pp. 1486-1496.
The paper (PDF) "The Clusters AgeS Experiment (CASE): Variable Stars in the Globular Cluster M4"
Kaluzny, J.; Thompson, I. B.; Rozyczka, M.; Krzeminski, W.;
2013, Acta Astronomica, vol 63, no 2, p. 181-201
The paper (PDF) "The Cluster AgeS Experiment (CASE). V. Analysis of Three Eclipsing Binaries in the Globular Cluster M4"
Kaluzny, J.; Thompson, I. B.; Rozyczka, M.; Dotter, A.; Krzeminski, W.; Pych, W.; Rucinski, S. M.; Burley, G. S.; Shectman, S. A.;
2013, The Astronomical Journal, Volume 145, Issue 2, article id. 43, 13 pp.
The reference
V-band image


Table 1: Basic properties of variable stars in M4 identified within the present survey
Star RA [2000.] Decl. [2000.] Period [days] Vmax B-V ΔV ΔE(B-V) PMa Typeb V light-curvec B light-curvec Remarks
V44 16:23:21 -26:33:25 0.263584542(2) 17.746 0.987 0.19 -0.020 Y EW V44.dat B44.dat
V45 16:23:15 -26:30:18 0.60334 19.370 0.490 1.20 - N RRab - - data from 1997 paper
V46 16:23:47 -26:31:56 0.0871525535(3) 18.553 0.287 0.05 -0.005 Y sdB V46.dat B46.dat
V47 16:23:26 -26:29:12 0.269874785(2) 16.826 0.815 0.27 -0.005 Y EW V47.dat B47.dat
V48 16:23:37 -26:31:43 0.28269398(2) 16.805 0.812 0.31 -0.005 U EW, CX15 V48.dat B48.dat
V49 16:23:34 -26:32:02 0.297443902(1) 17.087 1.290 0.99 -0.007 N EW, CX13 V49.dat B49.dat
V50 16:23:31 -26:31:49 0.26599834(1) 17.251 0.830 0.48 -0.006 Y EW V50.dat B50.dat
V51 16:23:33 -26:31:09 0.303682374(3) 17.103 0.870 0.45 -0.001 Y EW V51.dat B51.dat
V52 16:23:31 -26:30:58 0.7785087(15) 16.863 0.950 0.13 -0.003 Y - V52.dat B52.dat
V53 16:23:38 -26:32:11 0.308448705(1) 15.757 0.594 0.23 -0.007 Y EW V53.dat B53.dat
V54 16:23:51 -26:34:42 0.25244661(1) 17.802 0.951 0.24 -0.008 Y EB V54.dat B54.dat
V55 16:23:46 -26:31:17 0.310703451(1) 16.722 0.809 0.41 0.001 Y EW V55.dat B55.dat
V56 16:23:34 -26:29:56 - 14.646 1.154 0.14 0.000 Y CX5, CX9 V56.dat B56.dat
V58 16:23:34 -26:31:35 0.2628216(1) 20.38 - 0.35 -0.001 U CX1 V58.dat B58.dat
V59 16:23:39 -26:29:55 0.71155962(4) 20.296 1.565 0.41 0.000 Y EA V59.dat B59.dat
V60 16:23:48 -26:32:12 0.370342607(7) 19.297 1.206 0.51 -0.005 Y EA V60.dat B60.dat
V61 16:23:42 -26:33:18 0.0413287(1) 15.683 0.590 0.01 -0.014 Y SX V61.dat B61.dat
V62 16:23:33 -26:36:13 0.04062724(10) 19.074 0.608 0.07 -0.040 N SX V62.dat B62.dat
V63 16:23:27 -26:32:27 - 17.670 0.101 0.03 -0.012 Y sdB? V63.dat B63.dat
V64 16:23:21 -26:31:02 0.040953844(9) 18.439 0.609 0.05 -0.008 N SX V64.dat B64.dat
V65 16:23:28 -26:30:22 2.29304564(26) 17.028 0.903 0.40 -0.006 U EA, CX30 V65.dat B65.dat
V66 16:23:32 -26:31:41 8.11130346(85) 16.843 0.878 0.70 -0.003 Y EA V66.dat B66.dat
V68 16:23:39 -26:30:31 0.0380887(1) 15.238 0.615 0.01 0.000 Y SX V68.dat B68.dat
V69 16:23:58 -26:37:18 48.188268(6) 17.011 0.902 0.74 0.011 Y EA V69.dat -
a Proper motion membership status — Y - member, N - field star, U - uncertain
b Variable type

EW - contact binary; EB - close ecppsing binary; EA - detached ecppsing binary;

RR - RR Lyrae type pulsator; SX - SX-Phenicis type pulsator; sdB - hot subdwarf;

CX - X-ray source from Bassa et al. (2004)

c Data columns:
  1. HJD - 2 400 000.0
  2. magnitude
  3. error of magnitude (dummy points are maked with the error=9.999)