J/AJ/146/135 Physical parameters of 29 M31 globular clusters (Agar+, 2013)
M31 globular cluster structures and the presence of X-ray binaries.
Agar J.R.R., Barmby P.
<Astron. J., 146, 135 (2013)>
=2013AJ....146..135A 2013AJ....146..135A
ADC_Keywords: Galaxies, nearby ; Clusters, globular ; Binaries, X-ray
Keywords: galaxies: individual: M31 - galaxies: star clusters: general -
X-rays: binaries
Abstract:
The Andromeda galaxy, M31, has several times the number of globular
clusters found in the Milky Way. It contains a correspondingly larger
number of low-mass X-ray binaries (LMXBs) associated with globular
clusters, and as such can be used to investigate the cluster
properties that lead to X-ray binary formation. The best tracer of the
spatial structure of M31 globulars is the high-resolution imaging
available from the Hubble Space Telescope (HST), and we have used HST
data to derive structural parameters for 29 LMXB-hosting M31 globular
clusters. These measurements are combined with structural parameters
from the literature for a total of 41 (of 50 known) LMXB clusters and
a comparison sample of 65 non-LMXB clusters. Structural parameters
measured in blue bandpasses are found to be slightly different
(smaller core radii and higher concentrations) than those measured in
red bandpasses; this difference is enhanced in LMXB clusters and could
be related to stellar population differences. Clusters with LMXBs show
higher collision rates for their mass compared to clusters without
LMXBs, and collision rates estimated at the core radius show larger
offsets than rates estimated at the half-light radius. These results
are consistent with the dynamical formation scenario for LMXBs. A
logistic regression analysis finds that, as expected, the probability
of a cluster hosting an LMXB increases with increasing collision rate
and proximity to the galaxy center. The same analysis finds that
probability of a cluster hosting an LMXB decreases with increasing
cluster mass at a fixed collision rate, although we caution that this
could be due to sample selection effects. Metallicity is found to be a
less important predictor of LMXB probability than collision rate,
mass, or distance, even though LMXB clusters have a higher metallicity
on average. This may be due to the interaction of location and
metallicity: a sample of M31 LMXBs with a greater range in
galactocentric distance would likely contain more metal-poor clusters
and make it possible to disentangle the two effects.
Description:
A search of the Hubble Legacy Archive (HLA) in 2012 June for WFPC2 or
Advanced Camera for Surveys (ACS) images yielded 29 M31 globular
clusters for which structural parameters had not previously been
analyzed in the context of Low-Mass X-ray Binaries (LMXBs)
association.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 50 51 New HST data for 29 globular clusters with
Low-Mass X-ray Binaries (LMXB)
table3.dat 136 204 Model-fitting results
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See also:
J/AJ/146/20 : Structural parameters for 79 GCs in M31 (Wang+, 2013)
J/A+A/531/A155 : HST photometry in six M31 globular clusters (Perina+, 2011)
J/AJ/141/61 : Star clusters in M31. II. (Caldwell+, 2011)
J/ApJ/725/200 : An updated catalog of M31 globular-like clusters (Fan+, 2010)
J/AJ/137/94 : Star clusters in M31 (Caldwell+, 2009)
J/MNRAS/392/L55 : GCs in M31 from K-band photometry (Peacock+, 2009)
J/A+A/471/127 : New globular clusters in M 31 (Galleti+, 2007)
J/AJ/133/2764 : M31 globular clusters structural parameters (Barmby+, 2007)
J/ApJS/161/304 : Star clusters in the MW and satellites (McLaughlin+, 2005)
J/A+A/373/63 : M31 second ROSAT PSPC survey (Supper+, 2001)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Globular cluster name (G1)
12- 16 A5 --- Cam Camera (ACS or WFPC2)
18- 22 A5 --- Flt Filter (F336W, F435W, F475W, F555W, F606W,
F814W)
24- 28 I5 s Exp Exposure time
30- 33 F4.2 mag E(B-V) Reddening (1)
35- 39 F5.2 mag (V-m)0 Extinction-corrected color (2)
41- 45 F5.2 [Sun] [Fe/H] Metallicity (3)
47- 50 F4.2 Msun/Lsun M/Lv Ratio of total mass to visual luminosity (4)
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Note (1): From Fan et al. (2010, cat. J/ApJ/725/200), except for B091D, BH16,
and NB21 from Caldwell et al. (2011, cat. J/AJ/141/61), and B159 from
Fan et al. (2008MNRAS.385.1973F 2008MNRAS.385.1973F).
Note (2): Where m is the observed-band magnitude. Used to convert measurements
to the V band (see Section 2.1).
Note (3): From Caldwell et al. (2011, cat. J/AJ/141/61).
Note (4): Computed using metallicity-dependent M/Lv for an age of 13Gyr (see
Section 2.1).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Globular cluster name (G1)
12- 15 A4 --- Cam Camera (WFC or WFPC)
17- 20 A4 --- Flt Filter (F336, F435, F475, F555, F606, F814)
22- 23 I2 --- Np Number of points
25- 27 A3 --- Mod Model code (1)
29- 35 F7.2 --- chi2 Unreduced Χ2 of best-fitting model
37- 43 F7.2 Lsun/pc2 Ibkg Model-fit background intensity
45- 50 F6.2 Lsun/pc2 e_Ibkg Uncertainty in Ibkg
52- 56 F5.2 --- W0 ? Model-fit central potential
58- 61 F4.2 --- E_W0 ? Upper 68% confidence interval in W0
63- 66 F4.2 --- e_W0 ? Lower 68% confidence interval in W0
68- 72 F5.2 --- c Model-fit concentration (2)
74- 77 F4.2 --- E_c Upper 68% confidence interval in c
79- 82 F4.2 --- e_c Lower 68% confidence interval in c
84- 88 F5.2 mag/arcsec2 mu0 Model-fit central surface brightness (3)
90- 93 F4.2 mag/arcsec2 E_mu0 Upper 68% confidence interval in mu0
95- 98 F4.2 mag/arcsec2 e_mu0 Lower 68% confidence interval in mu0
100-105 F6.3 [arcsec] logr0 Log of fitted angular scale radius
107-111 F5.3 [arcsec] E_logr0 Upper 68% confidence interval in logr0
113-117 F5.3 [arcsec] e_logr0 Lower 68% confidence interval in logr0
119-124 F6.3 pc logR0 Log of physical scale radius
126-130 F5.3 pc E_logR0 Upper 68% confidence interval in logR0
132-136 F5.3 pc e_logR0 Lower 68% confidence interval in logR0
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Note (1): Model code defined as follows:
K66 = King (1966AJ.....71...64K 1966AJ.....71...64K) model. This is the "standard" model used
when describing globular clusters and is characterized by a
single-mass, isotropic, isothermal sphere;
W = The Wilson (1975AJ.....80..175W 1975AJ.....80..175W) model is a slight modification of the
K66 model with an extra term in the distribution function that causes
Wilson models to be more spatially extended;
PL = The "Power-Law with core" model of Elson et al. (1987ApJ...323...54E 1987ApJ...323...54E)
is often used to describe young clusters;
K62 = The King (1962AJ.....67..471K 1962AJ.....67..471K) model is an analytical parameterization
of the surface brightness profile sometimes used in studies of
marginally resolved clusters.
Note (2): c=log(rt/r0) (r0=fitted scale radius, rt|I(rt)= 0).
Note (3): Extinction-corrected in the native bandpass of the data.
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Global notes:
Note (G1): B091D-D057 is a probable misprint for B091D-D058 (note from CDS).
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 21-Jul-2014