NGC 6539 / C1802-075
RA: 18:04:49.74  DEC: -07:35:09.1  (J2000)

(Most recent updates: 
Membership probability flag - 2024; Remaining data - March 2015)
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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
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ID       Position               Mem   Period <mag>  ampl  C Type  Notes/
         RA          Dec        Flag                              Remarks
=========================================================================
1        18:04:38.16 -07:31:27.6 f  ----     --     --      L?    f?;62
2        18:04:52.03 -07:34:32.5 m1 ----     --     --      L?    58
3        18:04:43.21 -07:35:22.2 m1 ----     --     --      L?    61
4        18:04:05.14 -07:35:03.9 u  ----     --     --      L?    f?;81
5        18:04:58.64 -07:34:39.3 m1 ----     --     --      L?    34
6        18:04:48.66 -07:34:52.0 m1 ----     --     --      L?    68
7        18:04:54.87 -07:34:12.6 m1 ----     --     --      L?    53
8        18:04:51.06 -07:35:24.5 m1 ----     --     --      L?    38
9        18:04:55.79 -07:32:16.4 f  ----     --     --      L?    f?;85
10       18:04:55.09 -07:36:31.8 m1 ----     --     --      L?    49
11       18:04:50.36 -07:34:55.4 m1 ----     --     --      L?    36
PSR      -- -- --     -- -- --   u  ----     --     --            1 msP
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Supplementary Notes

NGC 6539 is a metal rich globular cluster located in a rich, heavily
reddened field near the Galactic centre.  According to the 2010 update 
to the Harris (1996) catalogue, its [Fe/H]=-0.63 and a CM diagram by 
Baker et al. (2007) shows a strong red HB clump, characteristic of a
metal rich cluster.

The data for V1-11 are from the discovery paper by Baker et al. (2007)  
and the numbers in the remarks column are the ones that they used
in their paper.  All of these stars are considered to be long period
variables.  However, firm classifications could not be made because 
the observations were limited to a span of three nights in May and 
eight in June 1996 with a gap of 31 days between.  Based on the 
cluster's high metallicity, it is possible that some of them are Mira 
stars.

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Discovery of the variable stars in NGC 6539

  V1-11  = variables announced by
    Baker et al. (2007) with RA & dec from 2MASS identifications
    The numbers V1-11 have been assigned in this catalogue.  Baker's
    numbers are listed in the remarks column.

    Baker et al. also announced two additional variables: #14, a long 
    period variable, and #607, an RR Lyrae.  They concluded that 
    neither is a cluster member so they are not listed in the above
    table.  Furthermore,  Layden (private communication, 2015) noted
    that he was uncertain about the variability of #14.   It was so
    bright that there may have been saturation or liniarity issues
    with the CCD.


  PSR:  According to Paulo Freire's website at the Max Planck 
        Institute in Bonn (July 2024 version), there is 
        1 millisecond pulsar in NGC 6539.
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In her early catalogues, Sawyer (1939, 1955) noted that Baade had
discovered one variable on Mount Wilson plates, but no further
information was provided about the star.
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References

Baker, J. M., Layden, A. C., Welch, D. L., Webb, T. M. A. 2007, AJ, 133,
139

Harris, W. E. 1996, AJ, 112, 1487

Prudil Z., Arellano Ferro, A. 2024, MNRAS, 534, 3654

Sawyer, H. B. 1939,  Publ. DDO, 1, No. 4

Sawyer, H. B. 1955,  Publ. DDO, 2, No. 2 
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