The Clusters AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster M12
Kaluzny, J.; Thompson, I. B.; Narloch, W.; Pych, W.; Rozyczka, M.
Abstract:
The field of the globular cluster M12 (NGC 6218) was monitored between 1995 and 2009 in a search for variable stars. BV light curves were obtained for thirty-six periodic or likely periodic variable stars. Thirty-four of these are new detections. Among the latter we identified twenty 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 a total of 103 objects were found, of which 42 are proper motion members of M12, and another four are field stars. 55 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. We also report the discoveries of a radial color gradient of M12, and the shortest period among contact systems in globular clusters in general.

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Kaluzny, J.; Thompson, I. B.; Narloch, W.; Pych, W.; Rozyczka, M.;
2015, Acta Astronomica, vol 65, no 3, p. 267-282
The reference
V-band image (FITS)
From 1-m Swope telescope.
Astrometric solution
in the header.
The reference
V-band image (FITS)
From 2.5-m duPont telescope.


Table 1: Basic properties of variable stars in M12 identified within the present survey*
Star RA [2000] Decl. [2000] Period [days] Vmax B-V ΔV PMa Typeb V light-curvec B light-curvec Remarks
V01 16:47:23 -1:55:36 0.243185 18.93 0.72 0.25 Y EW V01.ph -
V02 16:47:33 -2:03:10 0.252125 18.31 1.18 0.12 N EW V02.ph -
V03 16:47:13 -1:57:26 0.210636 17.86 0.72 0.08 Y EW V03.ph -
V04 16:47:37 -1:54:53 0.233990 19.45 1.18 0.46 N EW V04.ph -
V05 16:47:10 -1:56:10 0.225502 18.71 0.67 0.13 U EW V05.ph -
V06 16:47:21 -1:54:53 0.256196 18.80 0.74 0.34 Y EW V06.ph -
V07 16:46:55 -1:59:26 0.257078 16.65 1.06 0.07 N EW V07.ph -
V08 16:47:21 -1:57:24 0.435135 16.48 0.35 0.07 Y EW/Ell,BS V08.ph -
V09 16:47:17 -1:56:31 0.444540 17.12 0.77 0.03 U EW/Ell V09.ph -
V10 16:47:05 -1:59:36 4.595098 19.06 0.71 0.34 Y EA V10.ph -
V11 16:47:15 -1:57:06 5.218589 18.26 0.72 0.36 Y EA V11.ph -
V12 16:47:17 -1:55:43 1.025114 16.09 0.37 0.10 Y EA,BS V12.ph -
V13 16:47:15 -1:56:45 0.734141 17.07 0.47 0.26 Y EA,BS V13.ph -
V14 16:47:14 -1:57:02 0.463846 17.58 0.54 0.62 Y EA/EB,BS V14.ph -
V15 16:47:14 -1:56:28 0.541709 17.13 0.38 0.16 U EA,BS V15.ph -
V16 16:47:29 -1:55:36 2.500325 17.30 0.83 0.45 N EA V16.ph -
V17 16:47:20 -1:51:58 2.279741 20.00 1.30 0.82 U EA V17.ph -
V18 16:46:52 -1:57:34 17.47090 16.46 0.90 0.65 N EA V18.ph -
V19 16:46:56 -2:00:33 - 19.64 0.83 0.97 Y EA V19.ph -
V20 16:47:20 -1:57:10 - 19.72 0.75 0.62 U EA V20.ph -
V21 16:47:14 -1:56:28 0.019636 17.11 0.41 0.06 Y SX,BS V21.ph -
V22 16:47:23 -1:55:41 0.034364 17.25 0.46 0.05 Y SX,BS V22.ph -
V23 16:47:17 -1:57:42 0.044294 16.70 0.41 0.08 Y SX,BS V23.ph -
V24 16:47:14 -1:53:52 0.045042 17.20 0.48 0.08 Y SX,BS V24.ph -
V25 16:47:03 -1:57:38 0.049034 17.02 0.55 0.17 Y SX,BS V25.ph -
V26 16:47:14 -1:59:37 1.843644 16.57 0.83 0.12 Y Sp? V26.ph -
V27 16:47:23 -2:01:04 11.36074 17.89 1.12 0.44 N Sp?,RG? V27.ph -
V28 16:47:16 -1:56:20 0.949850 13.85 1.00 0.04 Y Sp? V28.ph -
V29 16:47:14 -1:59:37 1.842144 16.58 0.75 0.10 Y Sp? V29.ph -
V30 16:47:15 -1:56:07 0.400692 16.39 0.50 0.03 Y Ell?,BS V30.ph -
V31 16:47:15 -1:57:19 0.405218 17.61 0.44 0.08 U Ell?,BS V31.ph -
V32 16:47:13 -1:57:15 0.499084 17.23 0.55 0.07 U Ell? V32.ph -
V33 16:47:15 -1:57:19 0.682552 17.53 0.47 0.09 Y Ell?,BS V33.ph -
V34 16:47:13 -1:58:01 0.352252 19.55 0.81 0.41 U Sp? V34.ph -
V35 16:47:12 -1:57:20 0.962294 17.95 0.63 0.07 U Ell? V35.ph -
V36 16:47:06 -1:57:34 0.774844 16.81 0.82 0.02 Y Ell? V36.ph -
* We follow the naming convention of von Braun et al. (2002), who are the discoverers of the first two variables listed in the table.
Their variable V1 is not the W Vir pulsator referred to as V1 by Clement et al. (1988).
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;

SX - SX-Phenicis type pulsator; Sp - spotted variable; Ell - ellipsoidal variable;

BS - blue straggler; RG - red giant.

c Data columns:
  1. HJD - 2 450 000.0
  2. V magnitude
  3. error of magnitude (dummy points are maked with the error=9.999)
  4. phase