NGC 6624 / C1820-303 (Updated September 2015) RA: 18:23:40.69 DEC: -30:21:38.8 (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 18:23:53.52 -30:18:42.3 R0 ---- 15.0 4.2 B M max;Note 2 18:23:49.35 -30:17:52.2 R0 ---- 18.3 0.7 B L max;f;Note 3 18:23:39.84 -30:20:50.3 R0 ---- 15.4 1.0 B L Note 4 18:23:37.52 -30:22:01.8 R0 ---- -- -- CST? Note 5 18:23:30.00 -30:19:04.1 R0 0.3467 16.4 0.6 B RR1? f?;Note PSR:A-F -- -- ---- -- -- PSR ======================================================================= Supplementary Notes NGC 6624 is a metal rich bulge cluster with [Fe/H] = -0.44 according to the 2010 revision of the Harris (1996) catalgue. A VI CM diagram published by Heasley et al. (2000) shows a prominent red HB. In the above table, the RA and dec for V1-5 are from Samus et al. (2009) The magnitudes, ammplitudes and classifications are from Liller & Liller (1976). According to the VizieR Service, V1-5 are all listed in the catalogue of VISTA Variables in the Via Lactea Survey DR1 (Minniti et al. 2014). but no periods have been published by the VISTA group. ======================================================================= Notes on individual stars V1: According to Vizier, this star is listed as a variable in the AAVSO International variable star index (Watson et al. 2006) where it is classified as a Mira variable with a possible period of 276 days, and R_C magnitude ranging from 11.3 to 15.3, based on MACHO data. However, the period is uncertain. V2: The magnitudes published by Liller & Liller (1976) indicate that this star lies well to the red of the cluster's CM diagram at a V magnitude level comparable to the HB stars. It has a spectral type of M7 according to Skiff's (2014) Catalogue of spectral classifications reported by the VizieR service. Therefore V2 is considered to be a field star. V3: Liller & Carney (1978) confirmed the variability of V3 and showed that it lies near the RG tip in the CM diagram. Thus it is considered to be a cluster member, but no period has been derived. V4: Liller & Liller (1976) noted that this star is part of a close pair and questioned its variable status. They did not list any magnitudes. V5: The magnitude and colour derived by Liller & Liller (1976) for V5 are appropriate for cluster membership. However, they also pointed out that the star was outside the cluster's tidal radius. It is therefore possible that the star belongs to the rich field surrounding the cluster. ======================================================================== Discovery of the variable stars in NGC6624: V1-4 = V1, V2, V11 and V14 of Fourcade et al. (1966) with x,y coordinates and an ID chart Fourcade et al. announced 33 variables, but only 4 of them were considered to be cluster members. Sawyer Hogg (1973) assigned the numbers V3 and V4 to FL #11 and #14. V5: Liller & Liller (1976) with an ID chart for V1-5 ----------------------------------------------------------------------- A possible quiescent cataclysmic variable (or LMXB) was announced by Deutsch et al. (1999). Dalessandro et al. (2014) followed up on this system with HST observations and identified a star that appeared to be the optical counterpart of the X-ray source Star 1. They called it COM_Star1. It exhibited sinusoidal variations with an amplitude of ~0.7 mag in F435W and an orbital period of ~98 minutes. However, they could not make a definitive conclusion on the nature of the system: whether it was a CV or LMXB. ------------------------------------------------------------------- PSR: According to Paulo Freire's website, there are 6 millisecond pulsars in NGC 6624. (www.naic.edu/~pfreire/GCpsr.html) ========================================================================= References Dalessandro, E., Pallanca, C., Ferraro, F. R., Lanzoni, B., Castiglione, C., Vignali, C., Fiorentino, G. 2014, ApJ, 784, L29 Deutsch, E. W., Margon, B., Anderson, S. F., Downes, R. A. 1999, AJ, 118, 2888 Fourcade, C. R., Laborde, J. R., Albarracin, J. 1966, Atlas y Catalogue de Estrellas Variables en Cumulos Globulares al sur de -29 degrees, Cordoba Harris, W. E. 1996, AJ, 112, 1487 Heasley, J. N., Janes, K. A., Zinn, R., Demarque, P., Da Costa, G. S., Christian, C. A. 2000, AJ, 120, 879 Liller, M. H. & Carney, B. W. 1978, ApJ, 224, 383 Liller, M. H. & Liller, W. 1976, ApJ, 207, L109 Minniti, D., Saito, R. K., Hempel, M., Lucas, P. W., Rejkuba, M., Toledo, I., Gonzalez, O. A. and 102 coauthors, 2014, "The VVV Survey: New Results (Part I)" in Formation and Evolution of the Galactic Bulge Conference Proceedings, 1 Samus, N. N., Kazarovets, E. V., Pastukhova, E. N., Tsvetkova, T. M., Durlevich, O. V. 2009, PASP, 121, 1378 Sawyer Hogg, H. 1973, Publ. DDO, 3, No. 6 Watson, C. L., Henden, A. A., Price, A. 2006, Soc. for Ast. Sci. Symp., 25, 47 =====================================================================