NGC 1851 / C0512-400 (Updated June 2020) 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 05:14:28.93 -40:02:56.5 R0 0.5206 16.050 1.37 V RR0 2 05:14:02.75 -40:02:24.4 R0 ---- -- -- CST? Note;=V51? 3 05:14:02.44 -40:01:20.6 R0 0.3222 16.054 0.48 V RR1 4 05:14:08.53 -40:02:17.0 R0 0.5851 16.127 0.98 V RR0 5 05:14:09.89 -40:02:11.8 R0 0.5879 16.039 0.67 V RR0 6 05:14:00.01 -40:03:04.2 R0 0.6066 16.092 0.88 V RR0 7 05:14:07.06 -40:04:42.9 R0 0.5852 16.044 1.11 V RR0 8 05:14:08.90 -40:02:26.9 R0 0.5110 16.072 1.26 V RR0 9 05:14:01.33 -40:02:05.8 R0 ---- 13.48 0.5 V L Note 10 05:14:10.95 -40:06:08.9 R0 ---- 16.119 0.62 V RR0 Note 11 05:14:12.64 -40:05:07.6 R0 0.6679 15.937 0.82 V RR0 12 05:13:59.84 -40:03:41.8 R0 0.5760 16.122 0.96 V RR0 13 05:14:06.73 -40:02:07.4 R0 0.2825 16.118 0.59 V RR1 14 05:14:12.85 -40:02:34.8 R0 0.5940 15.429 0.80 V RR0 blend 15 05:14:09.07 -40:02:01.1 R0 0.5413 16.016 1.30 V RR0 16 05:14:12.27 -40:02:51.9 R0 0.4887 16.107 1.19 V RR0 17 05:14:02.90 -40:03:50.2 R0 0.7003 16.101 0.53 V RR0 18 05:14:09.91 -40:00:13.5 R0 0.2721 16.067 0.51 V RR1 19 05:14:08.76 -40:03:25.2 R0 0.4052 15.851 0.47 V RR1 blend? 20 05:14:05.57 -40:03:16.8 R0 0.5595 15.935 0.74 V RR0 21 05:14:01.14 -40:01:53.6 R0 0.2685 16.111 0.50 V RR1 22 05:14:17.50 -40:01:00.8 R0 0.5594 16.084 0.98 V RR0 23 05:14:16.15 -40:03:47.5 R0 0.2658 16.112 0.26 V RR1 24 05:14:19.34 -40:04:23.9 R0 183.0 13.27 0.15 V Lb Note 25 05:13:55.80 -40:07:31.8 R0 0.1737 16.48 0.6 B EC? f?;Note 26 05:13:55.35 -40:01:10.9 R0 0.3287 16.111 0.46 V RR1 27 05:14:03.70 -40:03:05.8 R0 0.5232 16.084 1.02 V RR0 28 05:14:09.75 -40:03:10.4 R0 0.6467 16.082 0.68 V RR0 29 05:14:05.52 -40:02:20.8 R0 0.6035 15.991 0.82 V RR0 30 05:14:07.53 -40:02:59.2 R0 0.5394 15.868 0.90 V RR0 blend? 31 05:14:08.73 -40:03:07.9 R0 0.4267 15.964 0.61 V RR0 32 05:14:04.65 -40:02:15.7 R0 0.6597 16.119 0.53 V RR0 33 05:14:07.91 -40:03:13.9 R0 0.3412 16.121 0.53 V RR1 34 05:14:09.81 -40:03:03.2 R0 0.515 -- -- RR0 Note 35 05:14:08.28 -40:02:48.6 R0 0.321 -- -- RR1 Note 36 05:14:07.60 -40:02:41.8 R0 0.318 -- -- RR1 Note 37 12.26 -13.97 XA 0.350 -- -- RR1 38 3.52 -13.3 XA 0.750 -- -- RR0? 39 05:14:06.71 -40:02:56.4 R0 0.573 -- -- RR0 Note 40 05:14:06.5 -40:02:43 R0 0.503 -- -- RR0? Note 41 05:14:06.14 -40:02:48.3 R0 0.400 -- -- RR0? Note 42 -1.46 -3.1 XA 0.341 -- -- RR1 43 05:14:06.21 -40:02:44.6 R0 0.283 -- -- RR1 Note 44 05:14:06.18 -40:02:54.2 R0 0.253 -- -- RR1? Note 45 -4.68 17.77 XA 0.389 -- -- RR0 46 -7.06 -0.8 XA 0.297 -- -- RR1 47 05:14:05.08 -40:02:40.2 R0 0.283 -- -- RR1 Note 48 05:14:04.62 -40:03:00.8 R0 0.520 -- -- RR0 Note 49 -23.3 -1.8 XA 0.267 -- -- RR1 50 05:14:03.18 -40:03:23.8 R0 0.327 -- -- RR1 Note 51 05:14:02.75 -40:02:24.4 R0 0.509 14.87 -- RR0 blend;Note 52 05:14:02.44 -40:02:33.8 R0 0.401 -- -- ? Note 53 05:14:06.54 -40:02:50.1 R0 ---- -- -- RR1? 54 05:14:09.11 -40:02:54.6 R0 ---- 13.33 0.45 L 55 05:14:09.70 -40:03:14.7 R0 ---- 13.29 0.35 L X-1 05:14:06.43 -40:02:37.6 R0 ---- -- -- UCXB Note PSR 05:14:06.74 -40:02:50.0 R0 ---- -- -- MSP rotP=4.99ms =================================================================== Supplementary Notes V1-33 The RA and dec for V1-33 are from Samus et al. (2009). The periods, magnitudes, amplitudes and variability types for the RR Lyrae variables numbered up to V33 are from Walker (1998). The sources for the other variables are indicated in the Notes on individual stars. All of them are considered to be cluster members. V34-52 The data are from Sumerel et al. (2004) unless indicated otherwise in the notes on individual stars. V53-55 The data for V53-55 and PSR are from the discovery papers. Stetson et al. (2019) published photometry for numerous stars in the field around NGC 1851. This has proved to be useful for identifying some of the variables for which RA and dec were not previously published. A new investigation of the variable stars in NGC 1851 would be very helpful. ============================================= 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. V10: According to Walker (1998), the period is uncertain. P~ 0.50 or ~0.33 are both possibilities. V24, V25: The data listed for these two stars are from Wehlau et al. (1982). V24 was also investigated by Layden et al. (2010) who could not confirm variations from their data. 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. V34, V35, V48, V50, V52: No values for the RA and dec of any of these variables have been published. However, I derived provisional values based on a transformation between Sumerel's (2004) x,y and RA, dec for stars with known RA and dec. Then I searched the catalogue of Stetson et al. (2019) to look for suitable candidates. In selecting the best candidate I considered Stetson's mean V magnitude and "Vary" parameter. If its image is not blended, an RR Lyrae variable should have mean V between 15.8 and 16.2 mag and a "Vary" parameter greater than 1.0. 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 In the above table, Stetson's RA and dec have been listed for these stars. The periods and classification are from the discovery paper by Sumerel et al. (2004). V36, V39, V40, V41, V43, V44: These variables were independently discovered by Downes et al. (2004): their RR6, RR2, [either RR9 or RR10], RR8, RR11 and RR4 respectively. Corwin (2009, private communication) confirmed this. A further discussion of the Downes et al paper is given at the end of the section on "Discovery of the Variable stars" below. The RA and dec for these stars are the values published by Downes et al. (2004). The periods and classification are from the discovery paper by Sumerel et al. (2004). V47: According to Amigo (2011, private communication), V47 is probably the same star as NV3 of Amigo et al. (2011). Based on the star's location and period, this assumption appears to be correct. The RA and dec listed in the above table are from Amigo et al. The period and classification are from the discovery paper by Sumerel et al. (2004). V51: Layden et al. (2010) realized that V51 and V2 form a close pair so that their images were blended in earlier investigations. They pointed out that the southeastern of the two stars is variable and was announced as V51 by Sumerel et al. (2004). With the resolved data of Layden et al., the star still appears brighter and redder than the other RR Lyrae variables so they suggested that it must be blended with an unresolved red giant. The data listed in the above table for V51 are from Layden et al. 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 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 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. ID x" y" V34 38.77 -10.87 V35 22.18 4.31 V36 14.07 12.49 Downes RR6 V37 12.26 -13.97 V38 3.52 -13.3 V39 3.27 - 1.46 Downes RR2 V40 0.59 12.32 Downes RR9 or RR10 V41 -1.26 5.89 Downes RR8 V42 -1.46 -3.1 V43 -2.14 10.31 Downes RR11 V44 -2.73 0.83 Downes RR4 V45 -4.68 17.77 V46 -7.06 -0.8 V47 -14.92 14.48 Amigo NV3 V48 -21.22 -6.12 V49 -23.3 -1.8 V50 -38.58 -28.44 V51 -41.86 31.50 Layden V51 V52 -44.82 21.6 Some of these new variables were included in the field of an independent investigation by Downes et al. (2004) and Corwin (2009, private communication) who was one of the authors of the Sumerel paper provided identifications for these stars. Further discussion of the Downes data is included at the end of this section. In addition, V47 and V51 were discussed in subsequent investigations by Layden et al. (2010) and by Amigo et al. (2011). These are discussed in the section: Notes on individual stars. It would be useful to have more information about most of these variables. I have made identifications for V34, V35, V48, V50 and V52, based on Stetson's (2019) data. Unfortunately the remaining variables are in the crowded central region of the cluster where their images are seriously blended. 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 has been assigned in this catalogue. Downes et al. listed 10 other RR Lyrae candidates, but some of these were already announced by Sumerel et al. (2004). Further discussion of Downes' candidate variables is given below, at the end of this section. V54-55 Layden et al. (2010) with RA and dec These authors also identified seven stars as new suspected variables. X-1 = MX 0513-40 = 4U 0513-40 This variable X-ray source was announced by Clark et al. (1975). The variability of the optical component was detected by Zurek et al. (2009) who derived a 17 minute periodicity based on FUV observations. PSR = PSR J0514-4002A, a binary millisecond pulsar: NGC 1851A Freire et al. (2004) with RA and dec. (rotation period = 4.99 ms) --------------------- 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 has been 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 will assume 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. ==================================================================== References Amigo, P., Catelan, M., Stetson, P. B., Smith, H. A., Cacciari, C., Zoccali, M. 2011, in Carnegie Obs. Astrophys. Series, Vol. 5: RR Lyrae Stars, Metal-Poor Stars, and the Galaxy, ed. A. McWilliam = 2011arXiv1105.0896v1 Bailey, S. I. 1924, Harvard Bull., 802, 2 Clark, G. W., Markert, T. H., Li, F. K. 1975, ApJ, 199, L93 Clark, G. W. 1975, ApJ, 199, L143 Deutsch, E. W., Anderson, S. F., Margon, B., Downes, R. A. 1996, ApJ, 472, L97 Downes, R. 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