NGC 6121 / Messier 4 / C1620-264 (Updated February 2020) RA: 16:23:35.22 DEC: -26:31:32.7 (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 16:23:13.67 -26:30:53.6 R0 0.2889 13.43 0.44 V RR1 2 16:23:16.30 -26:34:46.6 R0 0.5357 13.41 0.96 V RR0 3 16:23:19.47 -26:39:57.0 R0 0.5067 13.01 -- V RR0 4 16:23:21.03 -26:37:11.6 R0 ---- 10.0 0.5 V SR Sam;Note 5 16:23:21.03 -26:33:05.8 R0 0.6224 13.37 0.33 V RR0 6 16:23:25.79 -26:26:16.3 R0 0.3205 13.45 0.43 V RR1 7 16:23:25.95 -26:27:41.9 R0 0.4988 13.42 1.06 V RR0 8 16:23:26.16 -26:29:41.6 R0 0.5082 13.32 1.11 V RR0 9 16:23:26.80 -26:29:48.0 R0 0.5719 13.30 1.11 V RR0 10 16:23:29.21 -26:28:54.3 R0 0.4907 13.33 1.25 V RR0 11 16:23:29.98 -26:36:24.5 R0 0.4932 13.40 1.07 V RR0 12 16:23:30.82 -26:34:58.9 R0 0.4461 13.58 1.28 V RR0 13 16:23:30.88 -26:27:04.0 R0 ---- 10.95 0.5 V SR Sam;Note 14 16:23:31.29 -26:35:34.5 R0 0.4635 13.59 1.23 V RR0 15 16:23:31.96 -26:24:18.1 R0 0.4437 13.69 0.92 V RR0 16 16:23:32.50 -26:30:23.0 R0 0.5425 13.34 0.89 V RR0 17 16:23:34.02 -26:31:07.8 R0 ---- -- -- CST Sam;Note 18 16:23:34.70 -26:31:04.6 R0 0.4788 13.36 1.12 V RR0 19 16:23:35.05 -26:25:36.3 R0 0.4678 13.38 1.24 V RR0 20 16:23:35.39 -26:32:35.9 R0 0.3094 13.19 0.23 V RR1 21 16:23:35.93 -26:31:33.6 R0 0.4720 13.19 1.13 V RR0 22 16:23:36.95 -26:30:13.0 R0 0.6031 13.33 0.48 V RR0 23 16:23:37.33 -26:31:56.1 R0 0.2986 13.19 0.43 V RR1 24 16:23:38.04 -26:30:41.8 R0 0.5468 13.33 0.86 V RR0 25 16:23:39.42 -26:30:21.3 R0 0.6127 13.23 0.83 V RR0 26 16:23:41.65 -26:32:41.1 R0 0.5412 13.25 1.24 V RR0 27 16:23:43.17 -26:27:16.3 R0 0.6120 13.21 0.91 V RR0 28 16:23:53.60 -26:30:05.3 R0 0.5223 13.19 1.01 V RR0 29 16:23:58.25 -26:21:35.1 R0 0.5225 13.28 1.08 V RR0 30 16:23:59.65 -26:32:34.3 R0 0.2697 13.32 0.51 V RR1 31 16:24:00.64 -26:30:42.0 R0 0.5052 13.20 0.86 V RR0 32 16:24:29.70 -26:32:02.5 R0 0.5791 13.18 0.76 V RR0 33 16:24:33.33 -26:20:58.1 R0 0.6148 13.03 0.95 V RR0 34 16:22:33.64 -26:24:46.6 R0 0.5548 14.02 -- V RR0 Note 35 16:23:06.59 -26:30:27.0 R0 0.6270 13.38 0.66 V RR0 36 16:23:19.45 -26:35:49.0 R0 0.5413 13.42 0.92 V RR0 37 16:23:31.60 -26:31:30.6 R0 0.2473 13.37 0.22 V RR1 38 16:23:32.87 -26:33:03.5 R0 0.5778 13.42 0.63 V RR0 Note 39 16:23:34.67 -26:32:52.1 R0 0.6240 13.43 0.42 V RR0 40 16:23:36.49 -26:30:44.2 R0 0.3853 13.13 0.43 V RR1 Note 41 16:23:39.50 -26:33:59.8 R0 0.2517 13.49 0.36 V RR1 42 16:24:02.00 -26:22:13.0 R0 0.3173 13.24 0.41 V RR1 43 16:25:07.47 -26:25:43.9 R0 0.3206 13.08 0.46 V RR1 Note 44 16:23:15.27 -26:31:17.3 R0 ---- 13.20 -- V CST Sam;Note 45 16:23:37.31 -26:34:09.3 R0 ---- 13.46 -- V CST Sam;Note 46 16:23:37.76 -26:34:01.8 R0 ---- 13.50 -- V CST Sam;Note 47 16:23:37.30 -26:33:19.2 R0 ---- 13.40 -- V CST Sam;Note 48 16:23:33.64 -26:32:00.9 R0 ---- 13.14 -- V CST Sam;Note 49 16:23:45.25 -26:31:28.4 R0 0.2275 13.32 0.08 V RR1 50 16:23:37.52 -26:30:10.3 R0 ---- 13.06 -- V CST Sam;Note 51 16:23:27.68 -26:33:06.9 R0 ---- 13.42 -- V CST Sam;Note 52 16:23:24.06 -26:30:27.8 R0 0.8555 13.11 0.31 V RR0 Note 53 16:23:14.43 -26:36:05.4 R0 ---- 10.88 -- V CST? RGtip;Note 54 16:23:42.82 -26:29:27.5 R0 ---- 12.66 -- V CST? RG;Note 55 16:23:45.93 -26:23:36.9 R0 ---- 13.24 -- V CST blueHB;Note 56 16:23:45.95 -26:33:38.8 R0 ---- 12.93 0.02 V E?/L? RG;Note 57 16:23:46.92 -26:33:43.9 R0 ---- 12.98 -- CST? Sam;Note 58 16:23:47.84 -26:32:05.9 R0 ---- 13.50 0.04 V CST? blueHB;Note 59 16:23:50.15 -26:33:23.8 R0 ---- 13.44 0.07 V CST? redHB;Note 60 16:23:45.23 -26:33:56.8 R0 ---- 13.56 0.03 V CST? RG;Note 61 16:23:29.76 -26:29:50.3 R0 0.2653 13.26 0.17 V RR1 62 =V55 63/K44 16:23:21.05 -26:33:25.0 R0 0.2636 17.746 0.19 V EW max;K13b 64/K45 16:23:15.06 -26:30:19.1 R0 0.6045 20.01 0.84 V RR0 f 65/K46 16:23:47.19 -26:31:56.5 R0 0.0872 18.553 0.05 V sdB max;Note 66/K47 16:23:25.57 -26:29:11.7 R0 0.2699 16.826 0.27 V EW max;K13b 67/K48 16:23:36.81 -26:31:44.1 R0 0.2827 16.805 0.31 V EW max;K13b 68/K49 16:23:34.35 -26:32:01.8 R0 0.2974 17.087 0.99 V EW max;f;K13b 69/K50 16:23:31.34 -26:31:48.4 R0 0.2660 17.251 0.48 V EW max;K13b 70/K51 16:23:33.22 -26:31:09.1 R0 0.3031 17.103 0.45 V EW max;Note 71/K52 16:23:31.50 -26:30:57.7 R0 0.7785 16.863 0.13 V ELL? max;f?;Note 72/K53 16:23:38.51 -26:32:10.8 R0 0.3084 15.757 0.23 V EW max;Note 73/K54 16:23:50.96 -26:34:42.1 R0 0.2524 17.802 0.24 V EB max;K13b 74/K55 16:23:45.78 -26:31:16.5 R0 0.3107 16.722 0.41 V EW max;K13b 75 16:22:51.68 -26:25:14.7 R0 0.2973 14.25 0.3 B RR1 Note 76 16:22:05.56 -26:21:43.1 R0 0.3058 13.68 -- V RR1 Note 77/K56 16:23:34.30 -26:29:55.9 R0 ---- 14.646 0.14 V E? max;Note 78/K57 16:23:36.73 -26:31:50.6 R0 ---- 15.20 -- V CST Note 79 16:24:01.20 -26:21:56.2 R0 1.2472 15.05 0.3 V ? RG;Note 80 16:23:48.94 -26:23:51.9 R0 ---- 15.64 0.05 V CST Note 81/K58 16:23:34.15 -26:31:34.6 R0 0.2628 20.38 0.35 V max;Note 82/K59 16:23:39.18 -26:29:54.8 R0 0.7116 20.296 0.41 V EA max;K13b 83/K60 16:23:47.50 -26:32:12.6 R0 0.3703 19.297 0.51 V EA max;K13b 84/K61 16:23:42.35 -26:33:17.9 R0 0.0413 15.70 -- V CST? Note 85/K62 16:23:32.62 -26:36:13.1 R0 0.0406 19.074 0.07 V SX max;f;K13b 86/K63 16:23:27.37 -26:32:26.6 R0 ---- 17.670 0.03 V sdB? max;K13b 87/K64 16:23:20.80 -26:31:02.2 R0 0.0410 18.44 -- V CST? f;Note 88/K65 16:23:28.41 -26:30:21.8 R0 2.2930 17.028 0.40 V EA max;K13b 89/K66 16:23:32.26 -26:31:41.1 R0 8.1113 16.843 0.70 V EA max:K13b 90/K68 16:23:38.59 -26:30:30.9 R0 0.0381 15.24 -- V CST? Note 91/K69 16:23:58.11 -26:37:18.9 R0 48.1883 17.011 0.74 V EA max;K13a 92 16:23:36.43 -26:30:42.8 R0 0.2863 13.32 0.46 V RR1 Note 93/N1 16:23:37.11 -26:33:01.8 R0 0.1832 21.77 0.2 V EC Note 94/N2 16:23:33.15 -26:33:12.6 R0 0.3785 22.03 0.7 V E max;Note 95/N3 16:23:41.48 -26:32:05.2 R0 0.6299 19.30 0.1 V EC? 96/N8 16:23:34.99 -26:32:24.2 R0 6.8533 18.96 0.4 V E max;Note 97/N9 16:23:33.51 -26:32:29.8 R0 1.9363 19.17 0.16 V EC 98/N11 16:23:35.08 -26:32:04.0 R0 3.2085 17.64 0.07 V EC 99/N12 16:23:34.67 -26:32:04.2 R0 2.6946 18.91 0.1 V EC 100/N13 16:23:38.09 -26:31:37.8 R0 3.2075 16.89 0.08 V EC 101/N16 16:23:36.65 -26:31:43.4 R0 2.0713 19.30 0.1 V EC 102/N17 16:23:39.71 -26:31:20.0 R0 3.8961 19.85 0.16 V EC 103/N18 16:23:36.90 -26:31:39.2 R0 2.1904 18.09 0.1 V EC 104/N21 16:23:35.54 -26:31:20.3 R0 5.2727 21.87 0.8 V E max;Note 105/N29 16:23:34.37 -26:30:58.9 R0 3.3588 17.56 0.09 V E max;Note 106/N32 16:23:28.53 -26:31:34.0 R0 5.9260 17.20 0.18 V E max;Note 107/N33 16:23:36.63 -26:30:21.8 R0 0.6607 15.76 0.08 V EC 108/N36 16:23:32.40 -26:30:45.5 R0 0.9720 17.65 0.08 V ? 109/N38 16:23:34.32 -26:29:59.4 R0 0.1859 21.95 0.6 V EC 110/C6 16:23:59.77 -26:29:43.6 R0 0.2630 18.06 0.4 V EW 111/C7 16:24:02.14 -26:30:51.9 R0 0.2716 18.90 0.6 V EW 112/NV4 16:25:09.48 -26:39:42.2 R0 0.3444 -- -- EW 113 16:23:28.07 -26:25:02.2 R0 4.6337 19.620 0.038 V EA Note 114 16:24:14.75 -26:27:51.2 R0 1.959 16.753 0.011 V ? Note 115 16:23:06.46 -26:27:50.9 R0 0.2045 19.645 0.023 V EW Note 116 16:23:24.57 -26:26:23.0 R0 0.2774 19.480 0.270 V EW Note PSR 16:23:38.22 -26:31:53.7 R0 ---- -- -- msP Note ====================================================================== Supplementary Notes M4 is a nearby cluster. According to the 2010 update of the Harris (1996) catalogue, it has core radius, half light radius and tidal radius of 1.16', 4.33' and 51.8' (arcminutes) respectively and a distance of 2.2 kpc, which makes it the closest globular cluster to the Sun. Early proper motion/membership studies of stars in M4 were carried out by Cudworth & Rees (1990) and by Zloczewski et al. (2012). Because of its proximity, M4 has been the subject of numerous investigations. In the latter decades of the 20th century, new variable stars were announced in a number of different studies, but there was not a comprehensive investigation that included them all. This omission was addressed by Stetson et al. (2014 - hereafter referred to as S14). Much of the data in the above table is from their paper. ----------- With the expansion of extraplanetary studies in the 21st century, M4 has become a popular target. Safonova et al. (2016 - hereafter referred to as Saf16) carried out a microlensing survey with the aim of detecting free-floating planets (FFPs). In the course of their work, they detected variable stars. A portion of M4 was in the field of the Kepler spacecraft's K2 mission in 2014. Wallace et al. (2019a,b - hereafter referred to as W19a, W19b)) analysed the data and detected 66 variable stars that were cluster members, 52 of which were new discoveries. Their light curves reached sub-millimagnitude precision which permitted them to detect asteroseismic activity in some of the stars. The results of these two studies are discussed below in the section on Discovery of the Variable Stars. --------------- Source of data in the above table V1-92, V110-111: The RA and dec for most of these stars are from S14. For stars with "Sam" indicated in the "remarks" column, the RA and dec are from Samus et al. (2009). The remaining data for these stars are also from S14 unless indicated otherwise in the "Notes on individual stars". If K13a/K13b is listed in the "Remarks column, the periods, magnitudes, amplitudes and classifications are from Kaluzny et al. (2013a/b). V93-109 (= N1, N2, etc.): All of the data for these variables are from the discovery paper by Nascimbeni et al. (2014) who used HST observations to search for variable stars in the core. --------------- For the remaining variables, the data are from the discovery papers, unless indicated otherwise in the "Notes on individual stars". ========================================================================= Notes on individual stars V4, V13: The mean V magnitudes and amplitudes are from photoelectric photometry published by Eggen (1972) who concluded that both appear to be semi-regular variables. He derived P ~ 65 days for V4 and P ~ 40 days for V13. A K_p band light curve for V13 plotted over a range of 80 days (August to November 2014) by W19b (Fig. 8) shows irregular variation with 4 maxima and 4 minima during the interval. Both stars are considered to be cluster members based on radial velocities derived by Joy (1949) and a mean cluster velocity derived by Kinman (1959). The RA and dec listed above are from Samus et al. (2009). V17, V52: V17 is NOT variable. The star listed as V17 by de Sitter (1947) and in previous versions of this catalogue, with P=0.8555, is actually V52. This was recognized by S14. De Sitter's (1947) paper was written by Oosterhoff after de Sitter's untimely death, but Oosterhoff did not have access to all of the original material. He was working from notes. In the paper, he pointed out that the location of V17 was uncertain. He was able to make successful matches for the other variables by referring to the work of Sawyer (1931) and to a preliminary report by de Sitter (1941). However, Oosterhoff did not know the position of the variable with a period of 0.8555 days so he assumed that it might be V17. It is now known as V52. The non-variable status of V17 was first pointed out by Sawyer (1931) and confirmed by S14. Both Samus et al. (2009) and S14 have noted that it is a red star. In the 2009 version of this electronic catalogue, a period of 0.4605 days was listed for V52. This was derived by Yao et al. (1980a,b), but the light curve plotted in their paper showed a lot of scatter. The 0.4605 day period is an alias for the true period, 0.8555 days. V34: The period was derived by de Sitter (1947) and later confirmed by Sujarkova & Shugarov (1981). S14 did not have sufficent data to fit a light curve. V38: The y coordinate published by Sawyer Hogg (1973) for V38 was incorrect. It should have been -92". This was a typing error; it was listed correctly in the 1955 edition of her catalog. V40/V92: De Sitter (1947) had difficulty deriving a period for this star because its image was blended with a nearby star on some of his plates. Nascimbeni et al. (2014) and S14 discovered that the nearby star was also an RR Lyrae variable. It was Nascimbeni's N31 and S14's C1. The nearby companion to V40 has been assigned the number V92 in this catalogue. V43: This star was outside the field observed by S14. The period, V magnitude and amplitude are from the study by Cacciari (1979). V44, V45, V46, V47: The RA and dec are from Samus et al. (2009), the V magnitudes are from Alcaino (1975). Alcaino stated that these stars might be RR Lyrae variables. However, S14 observed them and did not detect variability in any of them. They are therefore classified as "CST". V48, V50, V51 The RA and dec are from Samus et al. (2009) and the mean V magnitudes are from Lee (1977). Lee stated that these stars might be RR Lyrae variables. However, S14 observed them and did not detect variability in any of them. They are therefore classified as "CST". Yao (1993) showed that V48 (= Lee 1717 = Greenstein 172 = Alcaino 522) is a blue HB star. V52: See comments for V17. V53, V54, V55: The RA and dec are from Samus et al. (2009) and the V magnitudes are from S14. Yao et al. (1981a,b) plotted light curves based on about 2 hours of observations. These stars show low level variations (approximately 0.1 mag). Thus it is not certain that the stars actually vary. They are therefore listed as "CST?" in the above table. Later, Yao (1991) showed that V55 is a blue HB star and derived provisional periods, but the V amplitudes were very low (0.01 mag or less). S14 noted that V53 showed some evidence for variability on time scales of minutes to hours and that V54 and V55 showed some evidence of variations between some of the different observing runs, but no coherent variation within any single observing run. They stated that they would not have identified V54 or V55 as variable on the strength of their own data. V53 was not in the field observed by W19b. V54: W19b detected multiharmonic variability with an amplitude of approximately 1 millimag which is probably unrelated to the variability reported by Yao et al. (1981a,b). V55: W19b concluded that V55 should be classified as "CST" on the basis of their data. V56: The V magnitude, amplitude and location on the CM diagram are from Yao (1987). The classification is from S14 and Saf16. V57: The RA and dec are from Samus et al. (2009). They differ from the coordinates listed by S14 because there was a transcription error in the x,y coordinates listed for this star in the 2009 version of this electronic catalogue. This discrepancy was also pointed out by Saf16. The V magnitude is from Cudworth & Rees (1990). Yao (1986) showed that at least one of the red giant stars G265 (V56) or G266 (V57) is variable, but in a subsequent paper (Yao 1987), only V56 was listed as variable. Saf16 did not detect any variations in V57. It is therefore listed as "CST?". V58, V59, V60: V magnitudes, amplitudes and location on the CM diagram are from Yao (1987). The observations spanned a period of approximately 2 hours. During that interval, the light curves for all of these stars had a similar shape. Given that the amplitudes were all low, their variable status is is called into question and they are listed a "CST?". S14 noted that these showed some evidence of variations between some of the different observing runs, but no coherent variation within any single observing run. They stated that they would not have identified any of these stars as variable on the strength of their own data. V65/K46: The RA and dec are from S14 and the remaining data are from Kaluzny et al (2013b) who noted that the star is an sdB star that is an ellipsoidal variable, supporting a conclusion reached by O'Toole et al. (2006) in an earlier paper. Neither S14 nor Saf16 detected variability in V65. V70/K51: The RA and dec are from S14 and the remaining data are from K13b. S14 did not detect any variability in this star. However, K13b's period and classification were confirmed by Nascimbeni et al. (2014) and by Saf16. V71/K52: The period and magnitudes are from Kaluzny et al. (2013b) who conclude that this is a binary star that exhibits ellipsoidal variations and, on one occasion, a flare. Its average luminosity varies from season to season. V72/K53: The RA and dec are from S14 and the remaining data are from K13b. K13b's period and classification were confirmed by Nascimbeni et al. (2016) and by Saf16. V75: The period and magnitudes are from Yao (1988). S14 derived B=14.31, V=13.37 but did not have sufficient data to derive a period. Saf16 did not detected any variability. V76: The RA, dec and V magnitude are from S14. The period was derived by Yao (1977, 1978). S14 did not have sufficient data to derive a period. Saf16 derived a slightly shorter period, P=0.305736 days and noted that their value was close to the one (0.305725) listed in the ASAS catalog. V77/K56: This star is on the RGB and its average luminosity varies from season to season. However, Kaluzny et al. (2013b) showed that it also exhibits a low amplitude variability on a time scale of about 10 days which might indicate it is in a binary system. They pointed out that the star may be associated with a nearby X-ray source. S14 found that is was mostly constant in brightness, but on one night, it showed a decrease and an increae of 0.06 mag. V78/K57: This star is on the RGB and the RA, dec and V magnitude listed above are from S14. According to Kaluzny et al. (2013b), it is no longer considered to be variable, a conclusion confirmed by S14 and by Saf16. V79: The RA and dec are from S14. This variable star was identified as Greenstein #302 and Lee #3107 in the discovery paper by Yao et al. (2004a,b). The period, mean V magnitude and amplitude are from their discovery paper. Lee's (1977) magnitude was too bright because the star had an unresolved companion. S14 were not able to discern star #302 on Greenstein's chart. However, they located a blended pair of stars nearby and noted that the southeastern star of the pair showed strong evidence of variability. They identified this star as V79, but did not have enough data to make a classification. They derived V=15.07 which is comparable to Yao's result. Saf16 observed V79 and confirmed that the period was ~1.2 days. However, the light curve was very noisy. They attributed this to the possibility of multiple periods. V80 (Alcaino 66): The RA and dec are from S14. The magnitude and amplitude are from the discovery paper by Yao et al. (2006). They concluded that the star must an eclipsing variable or a rotating spotted star, if it is a cluster member. They derived a period of 0.948997, but there is a lot of scatter on the light curve. S14 and Saf16 did not detect any variability in this star. W19b noted that V80 is a subgiant memeber of the cluster and concluded that it should be designated as "CST" on the basis of their data. V81/K58: All of the data are from Kaluzny et al. (2013b) who concluded in a earlier study (Kaluzny et al. 2012) that it is the optical counterpart of the X-ray source CX1 and probably a binary. V84, V87, V90: These are stars (K61, K64, K68) that Kaluzny et al. (2013b) classified as SX PHe variables. They listed V amplitudes of 0.01, 0l05 and 0.01 mag respectively, but no light curves were plotted in their paper. S14 did not detect variabiity in any of them. Therefore, they are listed as "CST?" Furthermore, Saf16 pointed out that both V84 and V90 were located in the field investigated by Nascimbeni et al. (2014) and should have been detected by them if they were actually varying. V92: See the note for V40. V93, V94 and the other variables announced by Nascimbeni et al. (2014): The V magnitudes that these authors listed were obtained by cross-matching their catalogue with that of Sarajedini et al. (2007) and do not represent the intensity-weighted averages derived from light curves. For the detached eclipsing binaries, e.g. V94, it is assumed that these magnitudes probably represent the V mgnitude at maximum light. The V amplitudes listed for these variables in the above table were read from the light curves plotted in Figures 4 and 5 of the Nascimbeni et al. paper. V96, V104, V105, V106: These are N8, N21, N29, N32, all detached eclipsing binaries discovered by Nascimbeni et al. (2014) and the data listed in the above table are from their paper. These stars are expected to have two eclipses of similar depth. As a result, the period finding algorithm might find periods of half the true duration. Therefore the periods they published, which are listed in the above table for these stars, were doubled with respect to the best-fitting periodogram solution. V113 (W1601): In the above table, the RA, dec, period and classification are from W19b and the V magnitude is from Stetson et al. (2019). The amplitude is from W19b and represents the depth of the primary eclipses in Kp magnitudes. According to the CMD of Stetson et al. (2014) and the photometry of Stetson et al. (2019), V113 is located on the lower main sequence of the CMD. V114 (W4490): In the above table, the RA, dec, period and amplitude (Kp magnitude) are from W19b and the V magnitude is from Stetson et al. (2019). On a CMD published by W19b, W4490 is displaced approximately 1 mag redward of the lower giant branch, an unusual location for a cluster member, but according to their Table 1, it has a membership probability of 1.0 based on Gaia proper motions. They classified the star as a possible X-ray binary because it is located 2.8 arcseconds away from a ROSAT X-ray source reported by Verbunt (2001). V115, V116 (W293, W1318): W19b found that the variable signals for both of these stars were indistinguishably blended between two or more additional stars: W293 with W283 and W1318 with W1335 and W1246. W293 and W1318 were the components with the largest amplitude. Both stars were detected as variables in the Pan-STARRS1 survey (Chambers et al. 2016). In the above table, the positions, periods and classifications are from W19b and the V magnitudes are from Stetson et al. (2019). The amplitudes are from W19b and represent the depths of the primary eclipses in Kp magnitudes. According to the CMD of Stetson et al. (2014) and the photometry of Stetson et al. (2019), these stars are both located on the lower main sequence of the CMD. V115: According to J19b, both components of the blend, W283 and W293 are considered members, based on Gaia proper motions. V116: No proper motion data were available for W1335, one of the components of the blend with W1318. However, W19b stated that it was probably a cluster member based on photometric data. The other two components, W1318 and W1246, are considered to be members based on their proper motion. PSR: The data listed for PSR B1620-26 are from Thorsett et al. (1993). The pulsar belongs to a triple system in which the third body is believed to be a planet, a possibility first postulated by Backer et al. (1993). Other investigations of this object are reported on Paulo Freire's website (www.naic.edu/~pfreire/GCpsr.html). ====================================================================== Discovery of the Variable Stars in M4: V1-33 Leavitt & Pickering (1904) with x,y positions An ID chart was subsequently published by Sawyer (1931). V34-43 de Sitter (1947) with x,y positions for V34-43 and Greenstein's (1939) numbers for V35-42. Greenstein's paper included an ID chart. In an earlier report, de Sitter (1941) listed the x,y coordinates for these new variables V44 = Alcaino #246 V45 = Alcaino #381 V46 = Alcaino #382 V47 = Alcaino #505 These are HB stars that Alcaino (1975) indicated as variables in Table 3 of his paper. He labelled them on his ID charts. The numbers V44-47 were assigned by Clement (1997) in the first electronic update of the Sawyer Hogg (1973) catalogue. V48 = Lee #1717 = Greenstein 172 = Alcaino 522 V49 = Lee #3602 = Greenstein 140 = Alcaino 488 = ZB 19 V50 = Lee #3732 V51 = Lee #1610 V52 = Lee #2630 = Greenstein 37 = Alcaino 433 = ZB 18 These are HB stars that Lee (1977) considered to be RR Lyrae variables (V48-50) or suspected RR Lyrae variables (V51-52). See Table 3 of his paper. They were all labelled on finding charts in his paper. The numbers V48-52 were assigned by Clement (1997) in the first electronic update of the Sawyer Hogg (1973) catalogue. V49 (ZB 19, G140) and V52 (ZB 18, G37) were independently discovered by Yao (1980a,b) who listed their x,y coordinates and Greenstein (1939) numbers. The Alcaino (1975) numbers for Lee #3602 (V49) and Lee #2630 (V52) were published by Cudworth & Rees (1990) and the ID charts of Alcaino and Greenstein can be readily compared. V53 = ZB 44 = Greenstein 512 = Lee 1411 = Alcaino 219 V54 = ZB 38 = Greenstein 30 = Lee 3621 = Alcaino 464 V55 = ZB 39 = Greenstein 327 = Lee 3315 = Alcaino 64 suspected variables announced by Yao et al. (1981a,b) who identified them according to their Greenstein (1939) numbers. ID charts were published by Greenstein (1939). ZB is the abbreviation for Zhongguo Bianxing (Chinese Variable Star). The numbers V53-55 were assigned by Clement (1997) in the first electronic update of the Sawyer Hogg (1973) catalogue. In Table 1 of his paper, Alcaino (1975) indicated that Greenstein #512 and #30 were Alcaino #219 and #464 respectively and Cudworth & Rees (1990) listed their Lee numbers: #1411 and #3621. ID charts were published by Alcaino (1975) and by Lee (1977). In a subsequent paper, Yao (1991) listed the Alcaino and Lee numbers for Greenstein #327 (V55). V56 = ZB 37 = Greenstein 265 = Alcaino 375 = Lee 4508 V57 = ZB 43 = Greenstein 266 = Alcaino 374 = Lee 4509 suspected variables announced by Yao (1979a) who identified them according to their Greenstein (1939) numbers. ID charts were published by Greenstein (1939). ZB is the abbreviation for Zhongguo Bianxing (Chinese Variable Star). The numbers V56 and V57 were assigned by Clement (1997) in the first electronic update of the Sawyer Hogg (1973) catalogue. In Table 1 of his paper, Alcaino (1975) noted that the Greenstein #265 and #266 were Alcaino #375 and #374 respectively and Cudworth & Rees (1990) listed their Lee numbers: #4508 and #4509. ID charts were published by Alcaino (1975) and by Lee (1977). V58 = Greenstein 206 = Alcaino 491 = Lee 4632 V59 = Greenstein 481 = Alcaino 371 = Lee 4512 V60 = Greenstein 543 = Alcaino 376 = Lee 4507 suspected variables announced by Yao (1987) who identified them according to the numbers of Greenstein (1939), Alcaino (1975) and Lee (1977). ID charts were published in all three of these papers. The numbers V58-60 were assigned by Clement (1997) in the first electronic update of the Sawyer Hogg (1973) catalogue. V61 = Greenstein 46 = Alcaino 440 = Lee 2616 Yao (1988) with ID chart, x,y position and Greenstein (1939) number. The number V61 was assigned by Clement (1997) in the first electronic update of the Sawyer Hogg (1973) catalogue. A comparison of the ID charts of Greenstein and Alcaino shows that Greenstein #46 = Alcaino #440 and Cudworth & Rees (1990) listed Lee 2616 = Alcaino 440. V62 = V55 = Greenstein 327 = Alcaino 64 = Lee 3315 Yao (1991) with the Greenstein, Alcaino and Lee numbers The number V62 was assigned by Clement (1997) in the first electronic update of the Sawyer Hogg (1973) catalogue, but it is now known that this is the same star as V55 which was announced by Yao (1981a,b) in an earlier paper. V63-V74 are V44-V55 of Kaluzny et al. (1997) who published ID charts and 1950 RA and dec. The 2000 RA and dec listed in the above table are from S14. The numbers V63-V74 were assigned in the electronic update to Sawyer Hogg's 1973 catalog (Clement et al. 2001). V75 = ZB 36 = Greenstein 343 Yao (1979b) with x,y position and ID chart. Greenstein's 1939 paper also included an ID chart. ZB is the abbreviation for Zhongguo Bianxing (Chinese Variable Star). The number V75 was assigned in this electronic catalogue in 2009. V76 = ZB14 Yao (1977,1978) with x,y position and ID chart. ZB is the abbreviation for Zhongguo Bianxing (Chinese Variable Star). The number V76 was assigned in this electronic catalogue in 2009. V77-78 = variables numbered 56 and 57 of Mochejska et al. (2002) with RA, dec and ID charts The numbers V77 and V78 were assigned in this electronic catalogue in 2009. S14 did not detect variabiity in V78. V79 = Greenstein 302 = Lee 3107 Yao et al. (2004a,b) with Greenstein (1939) and Lee (1977) numbers and an ID chart The number V79 was assigned in this electronic catalogue in 2009. V80 = Alcaino 66 Yao et al. (2006) with RA and dec. Alcaino (1975) published an ID chart. The number V80 was assigned in this electronic catalogue in 2009. V81-90 = K58-K66, K68 Kaluzny et al. (2013b) with RA and dec Finder charts for K65 and K66 were published by Kaluzny et al. (2013a) and finder charts for the others were published by Kaluzny et al. (2013b). The numbers V81-90 were assigned in this electronic catalogue in 2016. V91 = K69 Kaluzny et al. (2013a) with RA, dec and a finding chart The number V91 was assigned in this electronic catalogue in 2016. V92 = N31 of Nascimbeni et al. (2014) who published RA and dec = C1 of S14 who published RA and dec. The authors of both of these investigations recognized that this RR Lyrae variable was a close companion to the RR Lyrae variable V40 that had not been adequately resolved in earlier photographic studies. The number V92 was assigned in this electronic catalogue in 2016. V93-109 = N1, N2, N3, N8, N9, N11, N12, N13, N16, N17, N18, N21, N29, N32, N33, N36, N38 New variables announced by Nascimbeni et al. (2014) and identified by their RA and dec Not included in this list is their N19, an eclipsing binary that is not a cluster member, based on its proper motion. The numbers V93-109 were assigned in the 2016 update to this electronic catalogue. V110-111 = C6, C7 New variables announced by S14 and identified by their RA and dec S14 announced five other new variables - C1 which is now known as V92 and C2-5 which are not cluster members, based on their location in the CM diagram. The numbers V110 and V111 were assigned in the 2016 update to this electronic catalogue. V112 = NV4 A new variable announced by Saf16 who published the RA and dec (J2000). It is also listed in the WISE catalogue of variable stars (Chen et al. 2018): WISE J1625095-263942 The number V112 was assigned in the 2020 update to this catalogue Saf16's investigation was a search for free floating planets (FFPs) in the field of M4. They detected a number of new variables and candidate variables, in addition to 30 that had been previously reported. However, they concluded that most of their new variables were not cluster members, based on a vector point diagram they plotted (Fig. 13 and section 7.4.1). They then plotted the possible members on a CM diagram and concluded that NV4 was the only cluster member. V113-116 = W1601, W4490, W293, W1318 New variables announced by W19b and identified by their RA and dec (J2000) The W19b investigation was based on data from the Kepler spacecraft. A portion of M4 was included in the field of the K2 mission in 2014 and the field was observed continuously over an 80 day interval. In their analysis of the data, W19b extracted light curves for 4554 objects, including 3784 cluster members, and searched for variability. They detected 66 variable stars that were cluster members, 52 of which were new discoveries, 24 non-member variables, of which 20 were new discoveries, and four variables with ambigious membership status. In addition, they discovered 67 suspected variables, 57 of which were cluster members. Their light curves reached sub-millimagnitude precision which permitted them to detect asteroseismic activity in some of the stars. W19b pointed out that their work was intended primarily as a work of breadth not depth. They performed a detailed analysis of only a few of the variables they detected. However, they invited other investigators interested in these objects to perform their own analysis in greater depth. To facilitate that, they made their light curves publicly available. Most of the new variables detected by W19b have pulsation amplitudes of a millimagnitude or less. This permitted them to detect asteroseismic activity in 7 stars on the horizontal branch (two of which were previously announced by W19a) and in 19 along the red giant branch. However, since these amplitudes are below the level listed in this catalogue, they have not been included in the above table.  V113-16, the four variables listed above all had amplitudes greater than 0.01 mag and were cluster members mentioned as noteworthy by W19b in the conclusion of their paper. PSR = PSR B1620-26 Lyne et al. (1988) reported the discovery of an 11-ms pulsar in M4 ---------------------------------------------------------------- Pietrukowicz et al. (2008) searched for dwarf novae in M4 and found none. Frandsen et al. (2007) observed 24 K giants in M4 in an attempt to detect photometric variability due to p-mode oscillations. 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