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J/AJ/103/460                              CCD photometry of M 71 (Hodder+, 1992)
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Deep CCD photometry and variable stars in the metal-rich globular cluster M 71
       Hodder P.J.C., Nemec J.M., Richer H.B., Fahlman G.G.
      <Astron. J. 103, 460 (1992)>
      =1992AJ....103..460H   (SIMBAD/NED Reference)
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ADC_Keywords: Clusters, globular; Photometry, CCD; Stars, variable

Abstract:
   Two sets of observations of the metal-rich globular cluster M 71 are
   presented. The first uses deep CCD exposures to derive a fiducial
   in V, B-V and compares this with a cluster of similar metallicity,
   47 Tuc. Comparison with oxygen enhanced theoretical isochrones leads
   to age estimates for M 71 of from ~14+/-2Gyr to ~16+/-2Gyr. Within
   the limits imposed by the quality of the data, no significant age
   difference between the two clusters is found. The second set of
   73 frames is used to search an overlapping 67"x104" area of the cluster
   for variable stars. Light curves and phase diagrams (where appropriate)
   are presented for all four of the variables discovered. One variable
   blue straggler (or SX Phe star) has been identified with a period of
   0.050d. Values for its mass depend, of course, on the assumed pulsation
   mode-(0.90+/-0.47)M_{sun}_ for the first overtone mode, and
   (1.57+/-0.83)M_{sun}_ for the fundamental mode. One of the variables,
   with a 0.0582d period, but with a magnitude 1.75mag below the main
   sequence turnoff may be a field star. Two candidate eclipsing binary
   systems were also found. The most likely orbital period of one is 0.372d.
   This value, and the shape of the light curve, suggest that it could be
   a W UMa type variable. No period was obtainable for the other candidate
   binary due to a lack of phase coverage. Further data is needed to confirm
   and strengthen these claims, and to check for cluster membership.


File Summary:
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  FileName      Lrecl  Records   Explanations
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ReadMe             80        .   This file
table2             47     1861   Photometry of M71
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Byte-by-byte Description of file: table2
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   Bytes Format  Units   Label    Explanations
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   1-  4  I4     ---     ID       Identification number
       5  A1     ---     Cud      [*] A '*' indicates Cudworth stars that have a
                                   cluster membership probability of 50% or more
   7-  8  A2     ---   n_ID       Note on the stars (1)
  12- 16  F5.1   pix     X        X position
  18- 23  F6.1   pix     Y        Y position
  27- 31  F5.2   mag     Vmag     V magnitude
  36- 40  F5.2   mag     B-V      B-V colour
  43- 47  F5.2   mag     U-B      U-B colour
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Note (1): Name of the variables discussed in section 4.
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Historical note: Keypunched at CDS

References: Cudworth K.M., 1985, AJ, 90, 65
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(End)                        Marie-Jose Wagner, Patricia Bauer [CDS] 05-Dec-1994