NGC 6681 / C1840-323 / Messier 70
RA: 18:43:12.76  DEC: -32:17:31.6  (J2000)

(Most recent updates: 
Membership probability flag - 2024; Remaining data - June 2016)
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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        18:43:16.70 -32:19:18.9 m1   0.402  15.85  0.7   B RR1
2        18:43:05.68 -32:27:16.7 u    0.318  15.35  0.5   B RR1   f?;V4082 Sgr
3        18:43:11.71 -32:18:23.5 m1   0.564  15.55  1.7   B RR0
4        18:43:23.30 -32:23:01.2 f    0.3    15.75  0.5   B RR?
5        18:43:02.60 -32:25:32.1 u    0.492  17.80  1.0   B RR0   f?;V4081 Sgr
6        18:43:12.02 -32:17:29.7 m1   0.3416 15.09  0.23  I RR1

PSR      -- -- --     -- -- --   u  ----     --     --            3 msPs
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Supplementary Notes 

NGC 6681 is located in the same region of the sky as the main body of the
Sagittarius dwarf galaxy.  CM diagrams by Brocato et al. (1996) and
Massari et al. (2013) show an extended blue HB.

The RA and dec for V1-5 are from Samus et al. (2009). 
The remaining data are from Liller (1983).

The data for V6 are from the discovery paper by Figuera Jaimes et al.
(2016).
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Discovery of the variable stars in NGC 6681:

  V1-2  = V1 and V3 of Rosino (1962)  who published x,y coordinates
    and an ID chart for five variables, V1-5
    Sawyer Hogg (1973) assigned the number V2 to Rosino's V3 because 
    Rosino's V2 was considered to be a field star.

  V3-5 
    Liller (1983) with x,y coordinates and an ID chart
    Kadla et al. (1996) pointed out that the x coordinates Liller
    published for V3 and V4 had an error in sign. The corrected
    coordinates are x=-8 (V3) and x=+142 (V4).
    Liller also published identifications for 13 field variables 
    including Rosino's V2, V4 and V5.

  V6
    Figuera Jaimes et al. (2016) with RA, dec and a finding chart.

  PSR:  According to Paulo Freire's website at the Max Planck 
        Institute in Bonn (July 2024 version), there are 
        3 millisecond pulsars in NGC 6681 (M70).
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Kadla et al. (1996) announced an additional 7 RR Lyrae variables, based
on B and V photometry they obtained for stars in the instability strip 
of the CM diagram.  They published x,y ccoordinates, but did not carry
out any further analysis.
Of Kadla's seven new variables, six should have been in the 41 by 41
arcsecond field observed by Figuera Jaimes et al. (2016). However, 
Figuera Jaimes et al. did not detect variability in any of them, with
the possible exception of one star.  The Kadla et al. chart is difficult 
to decipher, but it appears that their N7 might be V6.
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References

Brocato, E., Buonanno, R., Malakhova, Y., Piersimoni, A. M. 1996,
A&A, 311, 778

Figuera Jaimes, R., Bramich, D. M., Skottfelt, J., Kains, N.,
Jorgensen, U. G., Horne, K., Dominik, M. and 26 coauthors, 2016,
A&A, 588, A128

Kadla, Z. I., Gerashchenko, A. N., Malakhova, Yu. N.  1996, IBVS, 4414 

Liller, M. 1983, AJ, 88, 1463 

Massari, D., Bellini, A., Ferraro, F. R., van der Marel, R. P.,
Anderson, J., Dalessandro, E., Lanzoni, B. 2013, ApJ, 779, 81

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

Rosino, L. 1962,  Mem. SAI, 33, 351 = Asiago Contr. 132 

Samus, N. N., Kazarovets, E. V., Pastukhova, E. N., Tsvetkova, T. M.,
Durlevich, O. V. 2009, PASP, 121, 1378

Sawyer Hogg, H. 1973,  Publ. DDO, 3, No.  6
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