NGC 6642 / C1828-235 (Updated October 2014) RA: 18:31:54.10 DEC: -23:28:30.7 (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 18:31:53.13 -23:27:43.0 R0 ---- 13.1 -- V M V2578Sgr 2 18:31:55.38 -23:29:27.5 R0 0.436 16.7 2.0 B RR0 3 18:31:49.63 -23:28:26.6 R0 0.291 17.05 0.7 B RR1 4 18:31:54.05 -23:28:14.3 R0 0.287 16.95 0.9 B RR1? 5 18:31:54.43 -23:28:18.4 R0 ---- -- -- RR? 6 18:31:55.52 -23:29:03.6 R0 0.58 17.3 0.8 B RR0? altP=0.42 7 18:31:58.44 -23:29:57.5 R0 0.307 16.8 0.8 B RR1 8 18:31:40.65 -23:34:05.1 R0 0.444 17.15 0.7 B RR1 9 18:31:53.59 -23:29:15.8 R0 0.59 17.1 1.2 B RR0? 10 18:31:48.31 -23:31:00.1 R0 0.6680 16.9 1.2 B RR0 11 18:31:51.65 -23:27:34.7 R0 0.5540 17.1 1.4 B RR0 12 18:31:51.37 -23:27:39.4 R0 0.5450 17.2 1.2 B RR0 13 18:32:01.92 -23:28:21.8 R0 0.5500 17.15 0.9 B RR0? 14 18:31:52.85 -23:28:14.0 R0 0.2890 17.25 0.5 B RR1? 15 18:31:55.10 -23:28:36.6 R0 0.3110 17.35 0.7 B RR1? 16 18:31:52.26 -23:28:22.5 R0 0.4580 16.85 1.3 B RR0 17 18:32:20.56 -23:32:12.9 R0 0.5060 17.2 1.6 B RR0 18 18:32:21.23 -23:28:11.2 R0 0.5490 16.85 0.9 B RR0 ====================================================================== Supplementary Notes A CM diagram based on HST observations by Balbinot et al. (2009) shows a well populated blue straggler sequence and a well developed HB. The RA and dec for V1-18 in the above table are from Samus et al. (2009). The V magnitude for V1 is from Barbuy et al. (2006) and the period and classification are from Hoffleit (1972). The remaining data for V2-18 are from Hazen (1993). Barbuy et al. (2006) published V magnitudes for 9 of the RR Lyrae variables: V3-5, V7, V9, V11-13, and V15 and derived a mean V of 16.43 +/- 0.06 mag. They also showed that V1 lies near the RG tip in the CM diagram. ==================================================================== Discovery of the variable stars in NGC 6642: V1 (V2578 Sgr) & V2 = 145a & 145b of Hoffleit (1972) who listed the RA and dec for epoch 1900 and published a finder chart. The numbers V1 and V2 were assigned by Sawyer Hogg (1973). V3-18 Hazen (1993) with x,y coordinates and an ID chart Hazen also discovered 11 field variables and published their 1950 RA and dec and an ID chart. ================================================================== References Balbinot, E., Santiago, B. X., Bica, E., Bonatto, C. 2009, MNRAS, 396, 1596 Barbuy, B., Bica, E., Ortolani, S., Bonatto, C. 2006, A&A, 449, 1019 Hazen, M. L. 1993, AJ, 105, 559 Hoffleit, D. 1972, IBVS, 660 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 ==================================================================