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J/AJ/108/1786       Blue stragglers & variable stars 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
       GUHATHAKURTA P., YANNY B., BAHCALL J.N., SCHNEIDER D.P.
      <Astron. J. 108, 1786 (1994)>
      =1994AJ....108.1786G      (SIMBAD/NED Reference)
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ADC_Keywords: Clusters, globular; Stars, variable; Stars, blue; Photometry,
              UBV; Positional data 

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 0.1mag, 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
   0.29arcmin^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. [1993, ApJ, 408, L89] 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 1.4pc. 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>~8h.

Addresses:
   Guhathakurta P.                      raja@stsci.edu
      Space Telescope Science Institute, 3700 San Martin Drive,
      Baltimore, Maryland 21218
   Yanny B.                             yanny@guinness.ias.edu
   Bahcall J.N.                         jnb@sns.ias.edu
      Institute for Advanced Study, Princeton, New Jersey 08540
   Schneider D.P.                       dps@astro.psu.edu
      Institute for Advanced Study, Princeton, New Jersey 08540 and
      Department of Astronomy and Astrophysics, The Pennsylvania State
      University, University Park, Pennsylvania 16802


File Summary:
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 FileName    Lrecl    Records   Explanations
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ReadMe          80          .   This file
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
   6- 11  F6.2    arcsec  RAoff   Right ascension (J2000) offset from center (1)
  13- 18  F6.2    arcsec  DEoff   Declination (J2000) offset from center (1)
  20- 24  F5.2    mag     Vmag    V magnitude, Johnson system (2)
  26- 30  F5.2    mag     V-I     V-I color (2)
  32- 36  F5.2    mag     U-V     []? U-V color
      37  A1      ---   n_U-V     Note on U-V (3)
  39- 43  F5.2    mag     F555W   F555W magnitude (instrumental) (4)
  45- 49  F5.2    mag     F785LP  F555W-F785LP color (instrumental) (4)
  51- 57  F7.2    pix     X       X pixel coordinate
  59- 65  F7.2    pix     Y       Y pixel coordinate
      67  I1      ---     CCD     [5/8] PC CCD image on which star appears
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Note (1): 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"
Note (2): V magnitude and V-I color (Johnson system) magnitude zero points
          have been adjusted to match ground-based photometry of some
          brighter stars.
Note (3): 'a' indicates the star is located outside the area covered by
           the U image; 'b' indicates the star is not detected in U.
Note (4): F555W magnitude and F555W-F785LP color (instrumental). The
          zero points for these magnitudes are approximate and are based
          on the WF/PC-1 instrument handbook.
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Origin: AAS CD-ROM series, Volume 3, 1995
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(End)        Lee Brotzman [ADS] 31-Oct-1994,  Patricia Bauer [CDS]   16-Feb-1995