NGC 6218 / C1644-018 / Messier 12 (Updated March 2014) RA: 16:47:14.18 DEC: -01:56:54.7 (J2000) ============================================================ Bytes Format Explanation 1-8 A8 Star ID 10-32 A11,1x,A11 Position 34-35 A2 Units for position R0 denotes RA, DEC in the J2000 coordinates R5 denotes RA, DEC in the 1950 coordinates XA denotes X, Y in arcseconds XP denotes X, Y in pixels 37-44 F8.4 Period (days) 46-51 F6.3 Mean magnitude (or maximum magnitude if "max" is indicated in the remarks column) 53-57 F5.3 Light amplitude (range of variability) 59 A1 Colour for mean magnitude and amplitude e.g. B, V, R, I, J, K or P (for photographic). 61-65 A5 Type of variable (draft 2006 GCVS classifications) CST denotes non variable stars previously designated as variables 67-80 A19 Notes and Remarks (f denotes field star) "--" or "----" indicates no data available ========================================================================= ID Position Period ampl C Type Notes/ RA/X Dec/Y Units Remarks ========================================================================= 1 16 47 16.81 -01 57 59.6 R0 15.527 12.68 1.05 B CW 2 16:47:22.89 -01:55:35.8 R0 0.2432 18.818 0.3 V EC max ==================================================================== Supplementary Notes V1: Period, magnitude, amplitude and classification for V1 from Clement et al. (1988) The RA and dec are from Samus et al. (2009). V2: All the data for vB1 are from the paper by von Braun et al. (2002) ================================================================ Discovery of the variable stars in M12: V1 Sawyer (1938) with ID chart and x,y coordinates V2 = von Braun's M12-V1 von Braun et al. (2002) with ID chart, RA and dec von Braun et al. also discovered a field variable which they called M12-V2. It is a foreground WUMa. ----------------------------------------------------------------- Two suspected RR Lyrae (based on their positions in the CM diagram) were announced by Malakhova et al. (1997) with X,Y positions in pixels and an ID chart. Pietrukowicz et al. (2008) searched for dwarf novae in M12 and found none. Lu et al. (2009) identified 6 X-ray sources in M12 and suggested that there may be 2-5 active binaries or cataclysmic variables in the cluster. Zloczewski et al. (2012) have identified nine variable blue straggler stars in M12. They plotted their locations on a V-(B-V) plot on which they also indicated the locations of six fainter variables (see Figure 14 of their paper). Dynamical properties of M12 blue straggler stars have been investigated by Simunovic & Puzia (2014). ============================================================ References Clement, C. M., Sawyer Hogg, H., Yee, A. 1988, AJ, 96, 1642 Lu, T.-N., Kong, A. K., Bassa, C., Verbunt, F., Lewin, W. H. G., Anderson, S. F., Pooley, D. 2009, ApJ, 705, 175 Malakhova, Yu. N., Gerashchenko, A. N., Kadla, Z. I. 1997, IBVS, 4434 Pietrukowicz, P., Kaluzny, J., Schwarzenberg-Czerny, A., Thompson, I. B., Pych, W., Krzeminski, W., Mazur, B. 2008, MNRAS, 388, 1111 Samus, N. N., Kazarovets, E. V., Pastukhova, E. N., Tsvetkova, T. M., Durlevich, O. V. 2009, PASP, 121, 1378 Sawyer, H. B. 1938, Publ. DAO, 7, no.5 Simunovic, M. & Puzia, T. H. 2014, ApJ, 782, 49 von Braun, K., Mateo, M., Chiboucas, K., Athey, A., Hurley-Keller, D. 2002, AJ, 124, 2067 Zloczewski, K., Kaluzny, J., Rozyczka, M., Krzeminski, W., Mazur, B. 2012, Acta Ast., 62, 357 ========================================================================