NGC 6681 / C1840-323 / Messier 70 RA: 18:43:12.76 DEC: -32:17:31.6 (J2000) (Most recent updates: Membership probability flag - 2024; Remaining data - January 2025) ============================================================ Bytes Format Explanation 1-8 A8 Star ID 10-32 A11,1x,A11 Position 34-35 A2 Membership probability flag based on data published by Prudil & Arellano Ferro (2024) m1: prob >=0.85; m2: prob >=0.7 and <0.85; m3: prob >= 0.5 and <0.7; f: prob <0.5 u: no data available 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 Mem Period ampl C Type Notes/ RA Dec Flag Remarks ========================================================================= 1 18:43:16.70 -32:19:18.9 m1 0.4024 15.079 0.264 I RR1 2 18:43:05.68 -32:27:16.7 u 0.3173 14.624 0.292 I RR1 f?;V4082 Sgr 3 18:43:11.71 -32:18:23.5 m1 0.5632 15.063 0.837 I RR0 4 18:43:23.30 -32:23:01.2 f 0.2991 15.007 0.241 I RR1 5 18:43:02.60 -32:25:32.1 u 0.4907 17.648 0.829 I RR0 f?;V4081 Sgr 6 18:43:12.02 -32:17:29.7 m1 0.3417 15.097 0.148 I RR1 PSR -- -- -- -- -- -- u ---- -- -- 3 msPs =========================================================================== Supplementary Notes NGC 6681 is located in the same region of the sky as the main body of the Sagittarius dwarf galaxy. CM diagrams by Brocato et al. (1996) and Massari et al. (2013) show an extended blue HB. The RA and dec for V1-5 are from Samus et al. (2009). The RA and dec for V6 are from the discovery paper by Figuera Jaimes et al. (2016). All of these variables were observed in the OGLE survey of the Galactic bulge (Soszynski et al. 2019) where V1-6 are OGLE-BLG-RRLYR- 65619, 65565, 65593, 65644, 65549 and 65596 respectively. The periods, magnitudes, amplitudes and classifications listed above are their values. ====================================================================== Discovery of the variable stars in NGC 6681: V1-2 = V1 and V3 of Rosino (1962) who published x,y coordinates and an ID chart for five variables, V1-5. He considered his V1 and V3 to be cluster members and V2, V4 and V5 to be field stars. For this reason, Sawyer Hogg (1973) assigned the number V2 to Rosino's V3 and did not include the others in her catalogue. All five of Rosino's (1962) variables were included in the globular cluster variable star catalogue/atlas of southern globular clusters published by Fourcade et al. (1966). Since the Fourcade catalogue is not available in many libraries and has not been digitized, many of the stars listed in their catalogue may become lost to the literature on globular cluster variable stars. For this reason, Layden et al. (2025) published the RA and dec (J2000) and Gaia Source IDs for the variables that were not incorporated into subsequent catalogues. This includes Rosino's V2 (FL02), V4 (FL04), V5 (FL05) and V367 Sgr in the field of NGC 6681. V3-5 Liller (1983) with x,y coordinates and an ID chart Kadla et al. (1996) pointed out that the x coordinates Liller published for V3 and V4 had an error in sign. The corrected coordinates are x=-8 (V3) and x=+142 (V4). Liller also published identifications for 13 field variables including Rosino's V2, V4 and V5. V6 Figuera Jaimes et al. (2016) with RA, dec and a finding chart. PSR: According to Paulo Freire's website at the Max Planck Institute in Bonn (July 2024 version), there are 3 millisecond pulsars in NGC 6681 (M70). ----------------------------------------------------------------------- Kadla et al. (1996) announced an additional 7 RR Lyrae variables, based on B and V photometry they obtained for stars in the instability strip of the CM diagram. They published x,y ccoordinates, but did not carry out any further analysis. Of Kadla's seven new variables, six should have been in the 41 by 41 arcsecond field observed by Figuera Jaimes et al. (2016). However, Figuera Jaimes et al. did not detect variability in any of them, with the possible exception of one star. The Kadla et al. chart is difficult to decipher, but it appears that their N7 might be V6. ======================================================================== References Brocato, E., Buonanno, R., Malakhova, Y., Piersimoni, A. M. 1996, A&A, 311, 778 Figuera Jaimes, R., Bramich, D. M., Skottfelt, J., Kains, N., Jorgensen, U. G., Horne, K., Dominik, M. and 26 coauthors, 2016, A&A, 588, A128 Fourcade, C. R., Laborde, J. R., Albarracin, J. 1966, Atlas y Catalogue de Estrellas Variables en Cumulos Globulares al sur de -29 degrees, Cordoba Kadla, Z. I., Gerashchenko, A. N., Malakhova, Yu. N. 1996, IBVS, 4414 Layden, A. C., Revangelista, J., Gupta, S., Mittameda, M., Mulloy, E., Muslim, S. I., Olushola-Alao, T., Rishi, A. 2025, Astron. Nachr., 346, Issue 2 Liller, M. 1983, AJ, 88, 1463 Massari, D., Bellini, A., Ferraro, F. R., van der Marel, R. P., Anderson, J., Dalessandro, E., Lanzoni, B. 2013, ApJ, 779, 81 Prudil Z., Arellano Ferro, A. 2024, MNRAS, 534, 3654 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 Sawyer Hogg, H. 1973, Publ. DDO, 3, No. 6 Soszynski, I., Udalski, A., Wrona, M., Szymanski, M. K., Pietrukowicz, P., Skowron, J., Skowron, D. and 7 coauthors, 2019, AcA, 69, 321 =======================================================================