J/AJ/108/1786 Blue stragglers and variable stars in M3 (Guhathakurta+, 1994)
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 1994AJ....108.1786G
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.
Space Telescope Science Institute, 3700 San Martin Drive,
Baltimore, Maryland 21218
Yanny B.
Bahcall J.N.
Institute for Advanced Study, Princeton, New Jersey 08540
Schneider D.P.
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 [ab] reason of missing U (3)
39- 43 F5.2 mag F555W F555W magnitude (instrumental) (4)
45- 49 F5.2 mag F555-785 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) at (J2000): 13:42:11.7+28:22:39
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
(End) Lee Brotzman [ADS] 31-Oct-1994, Patricia Bauer [CDS] 16-Feb-1995