CDROM/AJ/V108/P1786      Blue Stragglers & Variables in M3 (Guhathakurta+ 1994)
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Globular Cluster Photometry with the Hubble Space Telescope. III. Blue
Stragglers and Variable Stars in the Core of M3
      Puragra Guhathakurta, Brian Yanny, John N. Bahcall, Donald P. Schneider
      <1994, AJ, 108, 1786>
      =1994AJ....108.1786G
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Abstract:
  This paper describes Hubble Space Telescope (HST)/Planetary Camera-I
  images of the core of the dense globular cluster M3 (NGC 5272).
  Stellar photometry in the F555W (V) and F785LP (I) bands, with a 1
  sigma photometric accuracy of about 0.1 mag, has been used to construct
  color-magnitude diagrams of about 4700 stars above the main-sequence
  turnoff within r <~ 1' of the cluster center.  We have also analyzed
  archival HST F336W (U) images of M3 obtained by the Wide Field/
  Planetary Camera-I Instrument Definition Team.  The UVI data are used
  to identify 28 blue straggler (BS) stars within the central 0.29
  arcmin^2.  The specific frequency of BSs in this region of M3,
  N(BS)/N(V<V(HB)+2) = 0.094 +/- 0.019, is about a factor of 2-3 higher
  than that found by Bolte et al. in a recent ground-based study of the
  same region, but comparable to that seen in the sparse outer parts of
  the same cluster and in HST observations of the core of the higher
  density cluster 47 Tuc.  The BSs in M3 are slightly more centrally
  concentrated than red giant branch stars while horizontal branch stars
  are somewhat less concentrated than red giants.  The radial
  distribution of V-selected subgiant and turnoff stars is well fit by a
  King model with a core radius r(core) = 28" +/- 2" (90% confidence
  limits), which corresponds to 1.4 pc.  Red giant and horizontal branch
  stars selected in the ultraviolet data (U < 18) have a somewhat more
  compact distribution (r(core) = 22.5").  The HST U data consist of 17
  exposures acquired over a span of three days.  We have used these data
  to isolate 40 variable stars for which relative astrometry,
  brightnesses, colors, and light curves are presented.  A Kolmogorov-
  Smirnov test indicates that, typically, the variability for each star
  is significant at the 95% level.  We identify two variable BS
  candidates (probably of the SX Phe type) out of a sample of ~25 BSs in
  which variability could have been detected.  Most of the variables are
  RR Lyrae stars on the horizontal branch.  All of them have periods
  P >~ 8 h.


File Summary:
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File Name    Lrecl    Records   Explanations
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table1.dat      67       4699   Stellar photometry and astrometry for M3
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Byte-by-byte Description of file: table1.dat
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   Bytes Format  Units    Label        Explanations
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   1- 4   I4      ---     ID         Stellar ID, in order of increasing RA
   5-11   F7.2    arcsec  RA        *Right ascension (J2000) offset from center
  12-18   F7.2    arcsec  DE        *Declination (J2000) offset from center
  19-24   F6.2    mag     V         *V magnitude, Johnson system
  25-30   F6.2    mag     V-I       *V-I magnitude
  31-36   F6.2    mag     U-V        []? U-V color
  37      A1      ---     f_B-V     *Flag for U-V
  38-43   F6.2    mag     F555W     *F555W magnitude (instrumental)
  44-49   F6.2    mag     F785LP    *F555W-F785LP color (instrumental)
  50-57   F8.2    pix     X          X pixel coordinate
  58-65   F8.2    pix     Y          Y pixel coordinate
  66-67   I2      ---     CCD        PC CCD image (5-8) on which star appears
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Notes for file: table1.dat
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RA, DE:
  The equinox 2000 coordinate offsets are relative to the star AC 999
  (ID #1426): RA_2000 = 13h 42m 11.7s; DE_2000 = +28d 22' 39"

V, V-I:
  V magnitude and V-I color (Johnson system) magnitude zeropoints have
  been adjusted to match ground-based photometry of some brighter stars.

f_U-V:
  'a' indicates the star is located outside the area covered by the U
  image; 'b' indicates the star is not detected in U.

F555W, F785LP:
  F555W magnitude and F555W-F785LP color (instrumental).  The zeropoints
  for these magnitudes are approximate and are based on the WF/PC-1
  instrument handbook.
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(End)                                             Lee Brotzman [ADS] 31-Oct-1994