NGC 6218 / C1644-018 / Messier 12
(Updated 2009)

RA: 16:47:14.18  DEC: -01:56:54.7 (J2000)

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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 
                    or P (for photographic).
61-65   A5         Type of variable (draft 2006 GCVS classifications)
                      NV denotes not variable
67-80   A19        Notes and Remarks  (f denotes field star)

 "--" or "----" indicates no data available
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ID       Position                     Period <mag>  ampl  C Type  Notes/
         RA/X        Dec/Y     Units                              Remarks
=========================================================================
1         34         -62         XA  15.527  12.68  1.05  B CW    Note
vB1      16:47:22.89 -01:55:35.8 R0   0.2432 18.818 0.3   V EC    max;Note
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Supplementary Notes and References

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Notes on individual stars

V1:     Period, magnitude, amplitude and classification for V1
        from Clement et al. (1988 AJ 96, 1642)

V2:     All the data for vB1 are from the paper by von Braun et al.
        (2002)

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Discovery of the variable stars in M12:
  V1
    Sawyer, Publ DAO,7, no.5 with ID chart and x,y coordinates

  vB1 =  M12-V1
    von Braun et al., AJ 124, 2067 (2002) with ID chart, RA and dec

  Field variable M12-V2 discovered by von Braun et al (2002)
    is a foreground WUMa.

  Two suspected RR Lyrae (based on their positions in the CM diagram)
    were announced by Malakhova et al. (1997, IBVS 4434) with X,Y
    positions in pixels and an ID chart

  Lu et al. (2009, arXiv:0904.2772, submitted to the ApJ) identified
    6 X-ray sources in M12 and suggested that there may be 2-5 active
    binaries or cataclysmic variables in the cluster

  Pietrukowicz et al. (2008, MNRAS 388, 1111) searched for
  dwarf novae in M12 and found none.
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