J/AJ/113/669 Stars in M13 core (Cohen+ 1997)
Globular Cluster Photometry with the Hubble Space Telescope. VI. WF/PC-I
Observations of the Stellar Populations in the Core of M13 (NGC 6205)
Cohen R.L., Guhathakurta P., Yanny B., Schneider D.P., Bahcall J.N.
<Astron. J. 113, 669 (1997)>
=1997AJ....113..669C 1997AJ....113..669C
ADC_Keywords: Clusters, globular ; Photometry
Mission_Name: HST
Abstract:
We study the dense core of the globular cluster Messier 13 (NGC 6205)
using pre-refurbishment Planetary Camera-I images obtained with the
Hubble Space Telescope. Short exposures (60s) through the F555W and
F785LP filters (similar to Johnson V and I, respectively) have been
used to obtain V and I photometry of 2877 stars brighter than V∼20 in
a 1.25arcmin2 region of the cluster including its core and extending
out to r∼66arcsec (2.3pc) from its center. The sample is complete to
V~=18.3 (the main sequence turnoff) and the 1σ photometric error
is about 0.1mag. We find 15 blue straggler star candidates and 10
other possible blue stragglers in this region of M13. Their specific
frequency is in the range F_(BSS)=0.04-0.07, comparable to what is
observed near the centers of other dense clusters. A comparison
between M13's observed V band stellar luminosity function and a
theoretical model (Bergbusch & Vandenberg, 1992ApJS...81..163B 1992ApJS...81..163B) for
the luminosity function of an old, metal-poor cluster shows that the
model predicts too few of the brightest red giants (V∼12.5-15) by a
factor of two relative to subgiants/turnoff stars (>6σ effect).
The radial distributions of red giants, blue stragglers, and subgiants
are consistent with one another, and are well fit by a King profile of
core radius r(core)=38±6arcsec (90% confidence limits) or
1.3pc. Stars in the blue horizontal branch of M13, however, appear to
be centrally depleted relative to other stellar types. We combine data
from three dense ``King model clusters,'' M13, M3, and 47 Tuc, and two
post core collapse clusters, M30 and M15, and compare the
distributions of various stellar types as a function of
(r/r_(half light)_) and (r/r(core)). The horizontal branch stars in
the combined sample appear to be centrally depleted relative to the
giants (97% significance), this depletion is only a 1-2σ effect
in each of the clusters taken individually. The blue stragglers in the
combined sample are centrally concentrated relative to the giants.
(Copyright) 1997 American Astronomical Society.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 55 6436 Stars in the core of M13
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See also:
J/AJ/107/1745 : HST UVI photometry of M15. II. (Yanny+, 1994)
J/AJ/108/1786 : Blue stragglers + variable stars in M3 (Guhathakurta+, 1994)
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 Identification number
6- 11 F6.2 arcsec dRA *R.A. J2000 offset from star #5540
13- 18 F6.2 arcsec dDE *Dec. J2000 offset from star #5540
20 I1 --- CCD PC number of the CCD
22- 25 F4.1 arcsec r Angular distance from center of M13
27- 31 F5.2 mag F555W F555W magnitude
33- 37 F5.2 mag F785LP ? F785LP magnitude
39- 43 F5.2 mag Vmag ? V magnitude
45- 49 F5.2 mag Imag ? I magnitude
51- 55 F5.2 mag V-I ? V-I color
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Note on dRA, dDE:
All positions are on the equinox J2000 coordinate system, and are measured
relative to the reference star U (#5540) whose coordinates are:
RA = 16h 41m 41.61s, DE = +36d 27' 42.06", accurate to about 0.25 arcsec.
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References:
Guhathakurta et al., Paper I. 1992AJ....104.1790G 1992AJ....104.1790G
Yanny et al., Paper II. 1994AJ....107.1745Y 1994AJ....107.1745Y, cat. J/AJ/107/1745
Guhathakurta et al., Paper III. 1994AJ....108.1786G 1994AJ....108.1786G, Cat. J/AJ/108/1786
Guhathakurta et al., Paper V. 1996AJ....111..267G 1996AJ....111..267G
Origin: AAS CD-ROM series, Volume 8, 1997 Lee Brotzman [ADS] 09-Apr-1997
(End) [CDS] 03-Jul-1997