NGC 6558 / C1807-317 (Updated April 2016) RA: 18:10:18.38 DEC: -31:45:48.6 (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 18:10:15.60 -31:45:54.0 R0 0.4666 15.638 0.831 I RR0 2 18:10:16.26 -31:45:03.4 R0 ---- -- -- CST? Note 3 18:10:21.64 -31:45:15.5 R0 0.5880 15.355 0.822 I RR0 4 18:10:13.27 -31:46:16.0 R0 0.5037 15.549 0.514 I RR0 5 18:10:13.48 -31:43:45.1 R0 0.7487 15.597 0.487 I RR0 f?;Note 6 18:10:15.88 -31:46:41.4 R0 0.3125 15.634 0.251 I RR1 7 18:10:25.62 -31:43:33.0 R0 ---- -- -- CST? Note 8 18:10:17.86 -31:48:55.3 R0 0.5745 15.480 0.765 I RR0 9 18:09:50.46 -31:46:37.2 R0 0.4545 15.603 0.850 I RR0 10 18:10:36.26 -31:45:31.2 R0 ---- 14.06 1.11 V L? 11 18:10:01.62 -31:42:05.3 R0 ---- 15.27 0.81 V L? 12 18:09:53.87 -31:43:25.8 R0 ---- 15.26 1.72 V L? 13 18:10:04.75 -31:40:24.8 R0 0.3610 15.546 0.240 I RR1 14 18:10:45.76 -31:46:20.2 R0 0.2650 15.501 0.298 I RR1 15 18:09:54.16 -31:48:10.7 R0 ---- 14.91 0.87 V L? 16 18:10:19.63 -31:46:05.9 R0 0.6875 15.417 0.190 I RR0 17 18:10:16.21 -31:45:42.3 R0 0.7558 15.252 0.126 I RR0 ======================================================================== Supplementary Notes NGC 6558 is a relatively metal poor, core collapsed cluster in the Galactic bulge. According to the 2010 version 0f the Harris (1996) catalogue, it has [Fe/H] = -1.32, a tidal radius of 9.5 arcminutes, and a half-light radius of 2.15 arcminutes. Soszynski et al. (2014) listed the cluster radius as 2.1 arcminutes. A VI CM diagram by Rich et al. (1998) shows an extended blue HB and a sparsely populated RGB. All of the data for the RR Lyrae variables are from the OGLE IV survey (Soszynski et al. 2014) where V1 = OGLE-BLG-RRLYR-14886 = BB#25 r=0.43' V3 = OGLE-BLG-RRLYR-14929 = BB#30 r=1.04' V4 = OGLE-BLG-RRLYR-14866 = BB#24 r=1.02' V5 = OGLE-BLG-RRLYR-14867 = BB#A = V4301 Sgr r=2.26' V6 = OGLE-BLG-RRLYR-14888 = BB#E2 r=0.93' V8 = OGLE-BLG-RRLYR-14897 = BB#26 = V4601 Sgr r=3.09' V9 = OGLE-BLG-RRLYR-14732 = BB#16 = V4595 Sgr r=5.82' V13 = OGLE-BLG-RRLYR-14809 r=6.07' V14 = OGLE-BLG-RRLYR-15057 r=6.01' V16 = OGLE-BLG-RRLYR-14912 = BB#29 r=0.51' V17 = OGLE-BLG-RRLYR-14892 r=0.32' The BB numbers refer to a paper by Blanco & Blanco (1997) and r refers to the distance from the cluster centre. The RA and dec for the "CST?" stars V2, V7 and the "L?" variables V10-12 and V15 are from Samus et al. (2009). The magnitudes and amplitudes for the "L?" variables (V10-12 and V15) are from Dominici et al. (1999). Neither Hazen (1996) nor Dominici et al. (1999) had sufficient data to make definitive classifications for these variables. None of them were listed in the OGLE III (Soszynski et al. 2013) catalogue of Long Period Variables. With distances of 4.0, 5.0, 5.6 and 5.5 arcminutes from the cluster centre, they are all located beyond Soszynski's cluster radius, 2.1 arcminutes. ====================================================================== Notes on individual stars V2, V7: Hazen (1996) could not confirm the variability of either of these stars and noted that both of them were seriously blended with nearby stars. Furthermore, neither of them has been detected in other surveys of variable stars in the region, e.g. Blanco & Blanco (1997) or the OGLE surveys. V5: On the basis of the apparent B magnitude, Hazen (1996) concluded that V5 is not a cluster member and Rich et al. (1998) reached the same conclusion. It is fainter than the other RR Lyrae variables. In the Ogle IV data (Soszynski et al. 2014), the mean V mag of V5 (16.810 mag) is fainter than that of the other RR Lyrae variables which have mean V magnitudes ranging from 16.2 to 16.6 mag and mean =16.446 +/-0.131. With a distance of 2.6 arcminutes from the cluster centre, it is beyond the 2.1 arcminute cluster radius published by Soszynski et al. (2014). It therefore seems probable that V5 is part of the rich field surrounding the cluster. ======================================================================== Discovery of the variable stars in NGC 6558: V1-9 Rosino (1962) with x,y coordinates and ID charts He also provided identifications for 14 variables in the surrounding field. They were listed as V10-22 and V738 Sgr V10-15 Hazen (1996) with x,y coordinates and an ID chart Hazen also identified V1-9. Hazen's V10-15 were NOT the stars that were listed as V10-15 by Rosino (1962) because his were considered to be field stars. V1-15 all lie within 6.3 arcminutes of the cluster centre, which was assumed to be the tidal radius when Hazen published her paper. Hazen also announced discovery of 36 new variables in the field around the cluster with x,y coordinates and ID chart. In addition, 11 of Rosino's 14 field variables were in the field of Hazen's investigation. V16-17 OGLE-BLG-RRLYR-14912, OGLE-BLG-RRLYR-14892 identified by RA and dec in the Ogle III survey (Soszynski et al. 2011a) who assigned the numbers V16-17. V16 was previously announced as star #29 by Blanco & Blanco (1997) who published Epoch 1950 RA and dec and an ID chart. ----------------------------------------------------------------------- The OGLE III survey of the Galactic Bulge also included catalogues of Type II Cepheids (Soszynski et al 2011b) and Long Period Variables (Soszynski et al. 2013). In these surveys, no type II Cepheids were announced within 2.1 arcminutes of the centre of NGC 6558, the radius listed by Soszynski et al. (2014). The LPV catalogue includes an OSARG variable: OGLE-BLG-LPV-222123 (r=0.79). Its V magnitude (16.38) seems faint for a cluster member and the star probably belongs to the rich field surrounding the cluster. ======================================================================== References Blanco, B. M., Blanco, V. M. 1997, AJ, 114, 2596 Dominici, T. P., Horvath, J. E., Medina Tanco, G. A., Teixeira, R., Benevides-Soares, P. 1999, A&AS, 139, 321 Harris, W. E. 1996, AJ, 112, 1487 Hazen, M. L. 1996, AJ, 111, 1184 Rich, R. M., Ortolani, S., Bica, E., Barbuy, B. 1998, AJ, 116, 1295 Rosino, L. 1962, Mem. SAI, 33, 351 = Asiago Contr. 132 Samus, N. N., Kazarovets, E. V., Pastukhova, E. N., Tsvetkova, T. M., Durlevich, O. V. 2009, PASP, 121, 1378 Soszynski, I., Dziembowski, W. A., Udalski, A., Poleski, R., Szymanski, M. K., Kubiak, M., Pietrzynski, G. and 4 coauthors, 2011a, Ac. A., 61, 1 Soszynski, I., Udalski, A., Pietrukowicz, P., Szymanski, M. K., Kubiak, M., Pietrzynski, G. , Wyrzykowski, L. and 3 coauthors, 2011b, Ac. A., 61, 285 Soszynski, I., Udalksi, A., Szymanski, M. K., Kubiak, M., Pietrzynski, G., Wyrzykowski, L., Ulaczyk, K. and 3 coauthors, 2013, Acta A., 63, 21 Soszynski, I., Udalski, A., Szymanski, M. K., Pietrukowicz, P., Mroz, P., Skowron, J., Kozlowski, S. and 6 coauthors, 2014, Ac. A. 64, 177 ========================================================================