NGC 6540 / Djorg3 / C1802-277
RA: 18:06:08.6  DEC: -27:45:55  (J2000)

(Most recent updates: 
Membership probability flag - 2024; Remaining data - March 2016)
============================================================
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
=========================================================================
ID       Position               Mem   Period <mag>  ampl  C Type  Notes/
         RA          Dec        Flag                              Remarks
=========================================================================
1        18:06:08.22 -27:45:52.2 f    0.2541 15.137 0.285 I RR1
2        18:06:09.00 -27:45:25.7 m2   0.4498 15.184 0.555 I RR0
3        18:06:09.59 -27:46:08.7 f    0.5013 14.989 0.533 I RR0
=======================================================================
Supplementary Notes

NGC 6540 was thought to be an open cluster until Bica et al. (1994)
showed it to be a thick disk globular cluster.
A near IR (K, J-K) CM diagram published by Valenti et al. (2010)
is characterized by a steep poorly populated RGB and a blue HB
which was also present in the optical CMD of Bica et al. (1994).
They estimated [Fe/H]=-1.29, based on the slope of the RGB, a value
that is in agreement with [Fe/H] = -1.40 +/- 0.40 derived by Cote 
(1999) for four stars from the equivalent of a few Fe I lines.

The data for the RR Lyrae variables are from the OGLE IV survey
(Soszynski et al. 2014).

=====================================================================
Discovery of the Variable Stars in NGC 6540

  V1-3 = OGLE-BLG-RRLYR-13297, OGLE-BLG-RRLYR-13300, 
         OGLE-BLG-RRLYR-13306  
     identified by RA and dec in the OGLE III survey (Soszynski et al.
     2011a).  The numbers V1-3 have been assigned in this catalogue.
----------------------------------------------------------------------
The OGLE III investigation of the Galactic Bulge also included 
catalogues of Type II Cepheids (Soszynski et al 2011b) and Long Period 
variables (Soszynski et al. 2013).  In these surveys, no variables were 
announced within 0.8 arcminutes of NGC 6540, the radius listed by 
Soszynski et al.  (2011a). 
======================================================================
References

Bica, E., Ortolani, S., & Barbuy, B.  1994, A&A, 284, 67

Cote, P. 1999, AJ, 118, 406

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

Soszynski, I., Dziembowski, W. A., Udalski, A., Poleski, R., Szymanski,
M. K., Kubiak, M., Pietrzynski, G. and 4 coauthors, 2011a, Ac. A., 61, 1

Soszynski, I., Udalski, A., Pietrukowicz, P., Szymanski, M. K., 
Kubiak, M., Pietrzynski, G. , Wyrzykowski, L. and 3 coauthors, 2011b, 
Ac. A., 61, 285 

Soszynski, I., Udalksi, A., Szymanski, M. K., Kubiak, M., Pietrzynski,
G., Wyrzykowski, L., Ulaczyk, K. and 3 coauthors,  2013, Acta A., 63, 21

Soszynski, I., Udalski, A., Szymanski, M. K., Pietrukowicz, P., Mroz,
P., Skowron, J., Kozlowski, S. and 6 coauthors,  2014, Ac. A. 64, 177

Valenti, E., Ferraro, F. R. & Origlia, L. 2010, MNRAS, 402, 1729

===============================================================