NGC 1851 / C0512-400 (Updated October 2024) RA: 05:14:06.76 DEC: -40:02:47.6 (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 05:14:28.94 -40:02:56.5 R0 0.5206 16.161 1.276 V RR0 2 05:14:02.75 -40:02:24.5 R0 ---- -- -- CST Note;=V51? 3 05:14:02.46 -40:01:20.7 R0 0.3221 16.068 0.512 V RR1 4 05:14:08.56 -40:02:17.2 R0 0.5854 16.197 0.770 V RR0 5 05:14:09.90 -40:02:12.1 R0 0.5878 16.015 0.580 V RR0 6 05:14:00.02 -40:03:04.4 R0 0.6066 16.094 0.916 V RR0 7 05:14:07.04 -40:04:43.4 R0 0.5852 16.151 1.038 V RR0 8 05:14:08.93 -40:02:27.2 R0 0.5110 16.154 0.939 V RR0 9 05:14:01.34 -40:02:06.0 R0 ---- 13.48 0.5 V L/SR Note;La10 10 05:14:10.96 -40:06:09.1 R0 0.4995 16.304 0.887 V RR0 11 05:14:12.65 -40:05:07.8 R0 0.6679 15.908 0.82 V RR0 12 05:13:59.85 -40:03:41.9 R0 0.5759 16.223 0.957 V RR0 13 05:14:06.77 -40:02:07.7 R0 0.2825 16.170 0.623 V RR1 f? 14 05:14:12.85 -40:02:34.9 R0 0.5940 15.413 0.376 V RR0 blend? 15 05:14:09.11 -40:02:01.4 R0 0.5413 16.140 1.184 V RR0 16 05:14:12.28 -40:02:52.1 R0 0.4887 16.111 1.142 V RR0 17 05:14:02.92 -40:03:50.4 R0 0.7048 16.073 0.534 V RR0 18 05:14:09.93 -40:00:13.6 R0 0.2721 16.078 0.527 V RR1 19 05:14:08.79 -40:03:25.3 R0 0.4052 15.852 0.409 V RR1 20 05:14:05.58 -40:03:17.0 R0 0.5595 16.161 0.739 V RR0 21 05:14:01.15 -40:01:53.9 R0 0.2685 16.107 0.518 V RR1 22 05:14:17.51 -40:01:00.7 R0 0.5594 15.804 0.500 V RR0 23 05:14:16.16 -40:03:47.4 R0 0.2658 16.187 0.26 V RR1 24 05:14:19.35 -40:04:23.9 R0 183.0 13.27 0.15 V Lb/SR Note;We82 25 05:13:55.81 -40:07:32.0 R0 0.1737 15.706 0.461 B EC f 26 05:13:55.36 -40:01:11.1 R0 0.3287 16.149 0.482 V RR1 27 05:14:03.72 -40:03:05.7 R0 0.5232 16.063 0.978 V RR0 28 05:14:09.76 -40:03:10.7 R0 0.6467 16.082 0.68 V RR0 Note;Wa98 29 05:14:05.54 -40:02:21.1 R0 0.6036 15.671 0.503 V RR0 30 05:14:07.56 -40:02:59.3 R0 0.5394 15.868 0.90 V RR0 Note;Wa98 31 05:14:08.75 -40:03:08.0 R0 0.75 15.973 0.603 V RR0 Note 32 05:14:04.68 -40:02:16.2 R0 0.6597 15.909 0.488 V RR0 33 05:14:07.93 -40:03:14.2 R0 0.3412 15.680 0.588 V RR1 blend 34 05:14:09.81 -40:03:03.3 R0 0.3450 15.989 0.520 V RR1 35 05:14:08.30 -40:02:48.6 R0 0.3182 16.137 0.370 V RR1 36 05:14:07.62 -40:02:42.5 R0 ---- -- -- RR f?;Note 37 05:14:07.56 -40:03:07.4 R0 0.3510 13.217 0.066 V RR1 f?;blend 38 05:14:06.77 -40:03:07.0 R0 0.6530 15.885 0.479 V RR0 39 05:14:06.64 -40:02:55.9 R0 ---- -- -- RR Note 40 05:14:06.50 -40:02:42.3 R0 ---- -- -- RR Note 41 05:14:06.22 -40:02:48.1 R0 ---- -- -- RR f?;Note 42 05:14:06.27 -40:02:56.9 R0 0.3097 14.648 0.360 V RR1 f 43 05:14:06.27 -40:02:44.6 R0 ---- -- -- RR Note 44 05:14:06.12 -40:02:53.5 R0 ---- -- -- RR f?;Note 45 05:14:06.00 -40:02:36.5 R0 0.2564 14.640 0.179 RR1 f?;blend 46 05:14:05.76 -40:02:55.4 R0 0.2897 14.637 0.141 RR1 f?;blend 47 05:14:05.07 -40:02:40.0 R0 0.2801 15.629 0.369 V RR1 f? 48 05:14:04.63 -40:03:00.9 R0 0.5209 15.176 0.547 V RR0 f 49 05:14:04.41 -40:02:56.5 R0 0.2658 14.174 0.077 V RR1 blend 50 05:14:03.18 -40:03:23.8 R0 0.3251 15.462 0.231 V RR1 f 51 05:14:02.75 -40:02:24.5 R0 0.5094 14.805 0.245 V RR0 Note;blend 52 05:14:02.44 -40:02:33.8 R0 0.6488 16.120 0.256 V RR0 53 05:14:06.54 -40:02:49.6 R0 0.3251 12.617 0.260 RR1 f?;blend 54 05:14:09.12 -40:02:54.8 R0 ---- 13.33 0.45 L La10 55 05:14:09.70 -40:03:14.9 R0 ---- 13.29 0.35 L La10 56 05:13:41.80 -39:58:52.3 R0 0.2507 18.381 0.273 SXP? 57 05:13:51.14 -40:02:37.2 R0 0.7142 16.106 0.141 RR0 58 05:14:07.05 -40:02:18.2 R0 0.5030 14.352 0.197 RR0 blend 59 05:14:08.96 -40:02:35.0 R0 ---- 13.35 0.4 L 60 05:14:09.21 -40:02:44.2 R0 ---- 13.42 0.37 L 61 05:14:07.67 -40:02:30.3 R0 ---- 13.27 0.43 L X-1 05:14:06.43 -40:02:37.6 R0 ---- -- -- UCXB Note PSR -- -- -- -- -- -- R0 ---- -- -- 15 msPs ========================================================================= Supplementary Notes The most comprehensive study of the variable star population in NGC 1851 was by Arellano Ferro et al. (2024, hereafter AF24). The periods, magnitudes, amplitudes and classifications for V1-61 are from the AF24 investigation, unless indicated otherwise in the Notes column, where La10 refers to Layden et al. (2010), Wa98 refers to Walker (1998), We82 refers to Wehlau et al. (1982) AF24 published RA, dec (J2000) and ID charts for all of variables V1-61. The RA and dec listed above for V1-61 are from their paper. In their study, AF24 also carried out a membership analysis. Stars they found to be field stars are designated f in the Notes/Remarks column; stars with uncertain membership status are designated f? and the remaining stars are cluster members. NGC 1851 has numerous millisecond pulsars according to Paulo Freire's website at the Max Planck Institute in Bonn. In addition, it was among the first clusters in which an X-ray source was detected (Clark et al. 1975). ============================================= Notes on individual stars V2 (=V51): Wehlau et al. (1978) noted that V2 was badly blended and might not be variable. Layden et al. (2010) recognized that the southeastern of the two stars in the blend is variable and that it coincides with V51, a new variable announced by Sumerel et al. (2004). V9: Wehlau et al. (1978) noted that V9 was badly blended and suspected that it was not variable. However, the CCD data of Layden et al. (2010) showed that the star is a long period variable. The magnitude, amplitude and classification for V9 in the above table are from Layden et al. V24: The period, magnitude and amplitude listed are from Wehlau et al. (1982). V24 was also investigated by Layden et al. (2010) who commented that its amplitude values were below their variability detection thresholds. However, they showed that the star is near the red giant tip in the CM diagram and concluded that it must be a low amplitude long period variable. V28, V30: The periods, magnitudes amplitudes and classification are from Walker (1998) who noted that V30 is very crowded. AF24 did not publish any results for these two stars. V31: Walker (1998) and AF24 derived different periods, 0.426653 and 0.755159 days resepctively. These are aliases. The 0.755 period has a more appropriate location in the period-amplitide relation plotted by AF24. However, on the AF24 light curve, there is a large phase shift (about 0.25) between their 2018 and 2019 data. Therefore their period needs some adjustment and a period 0f 0.75 days is listed in the above table. V36, V39, V40, V41, V43, V44: AF24 could not retrieve useful data for any of these stars because of crowding. However, they were all identified as probable RR Lyrae variables by Sumerel et al. (2004). Furthermore, Downes et al. (2004) showed that they were variable and that their position in the CM diagram appeared to be where RR Lyrae variables are located. Therefore they are classified "RR" in the above table. No periods are listed because the observations were not extensive enough to derive definitive values. More information about the Sumerel and Downes investigations is provided below, in the section on "Discovery of the variable stars in NGC 1851" V51: See note for V2. X-1 NGC 1851 was among the first clusters in which an X-ray source was detected (Clark et al. 1975) and the source was thought to be part of a binary system (Clark 1975). From HST WFPC2 observations, Deutsch et al. (1996) identified an ultraviolet-excess candidate (their star A) as the optical counterpart, which was confirmed by subsequent authors. The first detection of variation in the optical component was by Zurek et al. (2009) who derived a period of 17 minutes based on FUV observations with HST and confirmed that the object was a UCXB. The RA and dec listed above refer to the position that Homer et al. (2001) derived for the X-ray burster. For star A, they derived RA = 5:14:6.41 and dec = -40:02:38.22 based on USNO A-2 and RA = 5:14:6.42 and dec = -40:02:38.05 based on Tycho 2. ============================================================= Discovery of the variable stars in NGC 1851: V1-2 = HV 3732-3733, = Z and Y Col Bailey (1924) with x,y coordinates and 1900 RA and dec. The numbers V1 and 2 were assigned by Sawyer (1939) in the first edition of her variable star catalogue. V3-10 Fourcade et al. (1966) with x,y coordinates and an ID chart. V1 and 2 were also labelled on their chart. V11-14 Liller (1975) with ID chart for V1-14 V15-21 Wehlau et al. (1978) with an ID chart for V1-21, x,y coordinates for V11-21 and revised x,y coordinates for V3 and V7 because their positions were incorrectly given by their discoverers, Fourcade et al. (1966). V22-25 = Stetson's (1981) stars 55, 159, 168, 244 Stetson (1981) noted that these stars were all variable, but did not have enough data to follow up. He published an ID chart for the stars in his study. Wehlau et al. (1982) confirmed their variability, assigned the numbers V22-V25, and derived x,y coordinates. Wehlau et al. also published revised x,y coordinates for V18 because an incorrect position was given in their earlier paper (Wehlau et al. 1978). V26 = Stetson's (1981) star 340 Wehlau et al. (1982) with x,y coordinates. Stetson (1981) had noted that this star was located in the RR Lyrae instability strip of the CM diagram, but his data were not sufficient to detect any variation. Stetson's star #368 was also in the instability strip, but Wehlau et al. did not detect any variation. They concluded that the apparent location of #368 in the instability strip was due to its proximity to a blue star. V27-33 Walker (1998) with an ID chart for these 7 new variables. His ID chart also included the 22 RR Lyrae stars among V1-26. V34-52 Sumerel et al. (2004) with x,y coordinates based on epoch 1950. They did not publish an ID chart. Their new variables were detected by the image subtraction technique. They derived tentative periods. ID x" y" Period V34 38.77 -10.87 0.515 V35 22.18 4.31 0.321 V36 14.07 12.49 0.318 V37 12.26 -13.97 0.350 V38 3.52 -13.3 0.75? V39 3.27 - 1.46 0.573 V40 0.59 12.32 0.503 V41 -1.26 5.89 0.400 V42 -1.46 -3.1 0.341 V43 -2.14 10.31 0.283 V44 -2.73 0.83 0.253 V45 -4.68 17.77 0.389 V46 -7.06 -0.8 0.297 V47 -14.92 14.48 0.283 V48 -21.22 -6.12 0.520 V49 -23.3 -1.8 0.267 V50 -38.58 -28.44 0.327 V51 -41.86 31.50 0.507 V52 -44.82 21.6 0.401 It was challenging to determine the true identifcation for these variables. However, this was accomplished thanks to the contributions of numerous people, as follows: ---------------------------------- 1. Corwin (2009, private communication) and Downes et al. (2004) ---------------------------------- V36, V39, V40, V41, V43, V44 Some of Sumerel's new variables were included in the field of an independent investigation of NGC 1851 by Downes et al. (2004). Over an interval of 5 hours, on March 24, 1999, they obtained far-utraviolet observations of stars that were located in the region of the CM diagram occupied by RR Lyrae stars. Amplitudes of pulsation for RR Lyrae variables in this region of the spectrum are about 4 times larger than in the V band. As a result, they readily identified a number of RR Lyrae candidates based on their change of magnitude, but their data were not extensive enough to derive periods. They noted that nine of the Sumerel variables were in their field of view, but they were unsuccessful in matching them. However, Corwin who was one of the authors of the Sumerel paper provided the Downes identifications: V36=RR6, V39=RR2, V40=RR9 or RR10, V41=RR8, V43=RR11, V44=RR4. Further discussion of the Downes data is included at the end of this section. ------------------------ 2. Layden et al. (2010) ----------------------- V51 -------------------------------------- 3. Amigo (2011, private communication) -------------------------------------- V47 Amigo et al. (2011) announced four variables, NV1 to NV4, as part of some preliminary work on variable stars in CMa globular clusters. In a private communication, Amigo confirmed that their NV4 appears to be V21 and their NV3 could be the same star as V47. ------------------------- 4. Stetson et al. (2019) ------------------------ V34, V35, V48, V50, V52 Stetson et al. (2019) published photometry for numerous stars in the field around NGC 1851. This was useful for identifying some of the remaining variables for which RA and dec had not been previously published. I derived provisional transformation equations to compute RA and dec from x",y", using stars for which these values were already known. Then I searched Stetson's data base to select the best candidates. To do this, I considered his mean V magnitude and "Vary" parameter. If its image is not blended, an RR Lyrae variable in NGC 1851 should have mean V between 15.8 and 16.2 mag and a "Vary" parameter greater than 1.0. This approach led to the identification of 5 additional variables and their RA and dec (J2000) were published in the 2020 update to this catalogue. V34 = Stetson #34999 V=15.947, Vary = 1.899 V35 = Stetson #33018 V=15.997, Vary = 2.245 V48 = Stetson #27911 V=15.797, Vary = 5.784 V50 = Stetson #25965 V=16.032, Vary = 4.504 V52 = Stetson #25059 V=15.998, Vary = 2.238 All of these variables were recovered by AF24 and the periods they derived were in good agreement with those published by Sumerel (V35, V48, V50) or aliases (V34, V52). ------------ 5. AF24 ----------- V37, V38, V42, V45, V46, V49 Because the RA and dec had been determined for 13 of Sumerel's variable stars, AF24 were able to match these 6 remaining stars with variables they detected in their investigation. All but V38 are severely blended and therefore their V magnitudes are much brighter than expected for RR Lyrae variables in NGC 1851. AF24 published their RA and dec (J2000) and an ID chart. V53 = RR7 Downes et al. (2004) with RA, dec and ID chart. The variability of this star was confirmed by Corwin (2009, private communication). The number V53 was assigned in an earlier version of this catalogue. V54-55 Layden et al. (2010) with RA and dec These authors also identified seven stars as new suspected variables. V56-61 AF24 with RA, dec (2000) and ID chart They noted that V57, V58, V59, V60, V61 were also reported in the Gaia-D3 database and were listed as G3, G10, G11, G13 and G14 respectively. They observed a number of other candidate variables in Gaia-D3, but did not confirm their variability. AF24 also discovered two RR Lyrae variables that they considered to be field stars (F1, F2). X-1 = MX 0513-40 = 4U 0513-40 This variable X-ray source was announced by Clark et al. (1975). The RA and dec listed above refer to the position that Homer et al. (2001) derived for the X-ray source. The variability of the optical component was detected by Zurek et al. (2009) who derived a 17 minute periodicity based on FUV observations. PSR: According to Paulo Freire's website at the Max Planck Institute in Bonn (July 2024 version), there are 15 millisecond pulsars in NGC 1851. --------------------- Suspected RR Lyrae variables identified in other studies Saviane et al. (1998) listed 7 RR Lyrae candidates with x,y positions. They selected their candidates by comparing their observed V magnitudes with the V magnitudes published by Walker (1992) for a CM diagram study. In addition, they used their data to derive a mean V magnitude for the previously known RR Lyrae in the cluster and calculated the differences between the observed V magnitudes of their candidates and this mean. Based on these two sets of differences, they selected 7 candidates. Their best four candidates, n1-4, were detected as variables in subsequent studies and are V50, V29, V27 and V32, respectively, in the above table. ------------------------ Downes et al. (2004) listed 11 RR Lyrae candidates with RA and dec (2000) and ID charts. They based their selection on HST far ultraviolet photometry obtained over an interval of 320 minutes, in a 25 by 25 arcsec field around the cluster core. Corwin (2009, private communication) who was a co-author of the Sumerel et al. paper investigated these candidates and reached the following conclusions. RR1 = a possible variable RR2 = V39 RR3 = a possible variable RR4 = V44 RR5 = a possible variable RR6 = V36 RR7 = V53 [new variable not listed by Sumerel; the number V53 was assigned in this catalogue] RR8 = V41 [If RR8 is V41, the x,y coordinates published by Sumerel are incorrect. According to Sumerel's x coordinate, RR8 should have an RA value between V40 (RR9/10) and V43 (RR11). However Downes' RA indicates that RR8 is west of both stars. This is also confirmed in their ID chart. I have assumed that Corwin made the correct identification for V41 (RR8). RR9 or RR10 = V40 [RR9 and RR10 were not resolved as separate stars in the Sumerel et al. data but, according to Corwin, one of them is probably V40.] RR11 = V43 ------------------------- Amigo et al. (2011) announced four variables, NV1 to NV4, as part of some preliminary work on variable stars in CMa globular clusters. Their NV4 appears to be V21 and according to Amigo (2011, private communication); their NV3 could be the same star as V47. --------------------------------------------------------- Zurek et al. (2016) detected a variable star with an 18.05 minute period in far-ultraviolet images obtained with the HST. They published FUV and optical images to identify the object. 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