J/ApJ/876/59 Chandra X-ray sources in the globular cluster 47 Tuc (Cheng+, 2019)
Exploring the mass segregation effect of X-ray sources in globular clusters:
the case of 47 Tucanae.
Cheng Z., Li Z., Li X., Xu X., Fang T.
<Astrophys. J., 876, 59 (2019)>
=2019ApJ...876...59C 2019ApJ...876...59C
ADC_Keywords: Clusters, globular; X-ray sources
Keywords: binaries: close ; globular clusters: individual (NGC 104) ;
stars: kinematics and dynamics ; X-rays: binaries
Abstract:
Using archival Chandra observations with a total exposure of 510ks, we
present an updated catalog of point sources for globular cluster (GC)
47 Tucanae. Our study covers an area of ∼176.7'2 (i.e., with
R≲7.5') with 537 X-ray sources. We show that the surface density
distribution of X-ray sources in 47 Tuc is highly peaked in the
cluster center, rapidly decreases at intermediate radii, and finally
rises again at larger radii, with two distribution dips at R∼100" and
R∼170" for the faint (LX≳5.0x1030erg/s) and bright
(LX≲5.0x1030erg/s) groups of X-ray sources, respectively. These
distribution features are similar to those of blue straggler stars
(BSSs), where the distribution dip is located at R∼200". By fitting
the radial distribution of each group of sources with a "generalized
King model", we estimated an average mass of 1.51±0.17M☉,
1.44±0.15M☉ and 1.16±0.06M☉ for the BSSs, bright X-ray
sources, and faint X-ray sources, respectively. These results are
consistent with the mass segregation effect of heavy objects in GCs,
where more massive objects drop to the cluster center faster and their
distribution dip propagates outward further. Besides, the peculiar
distribution profiles of X-ray sources and BSSs are also consistent
with the mass segregation model of binaries in GCs, which suggests
that, in addition to the dynamical formation channel, primordial
binaries are also a significant contributor to the X-ray source
population in GCs.
Description:
The central region of 47 Tuc has been observed 19 times by the Chandra
Advanced CCD Imaging Spectrometer (ACIS) from 2000 March to 2015
February. Five observations in 2000 March were performed with the
ACIS-I CCD array at the telescope focus, while the rest were taken
with the aim point at the S3 chip. As listed in Table 1, 13
observations were performed with a subarray mode, to minimize the
effect of pileup for bright sources.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
00 24 05.67 -72 04 52.6 47 Tuc = NGC 104
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File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 87 19 Log of Chandra observations
table2.dat 184 537 Main Chandra source catalog
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
V/150 : Updated cat. of variable stars in globular clusters (Clement+ 2017)
J/A+AS/113/299 : Abundances & vel. for cluster giants (Minniti 1995)
J/AJ/109/218 : Catalogue of globular cluster profiles (Trager+ 1995)
J/A+A/324/915 : Blue stragglers in M3 (Ferraro+ 1997)
J/ApJ/559/1060 : Variables in 47 Tuc (Albrow+, 2001)
J/other/Sci/292.2290 : Chandra compact binaries in 47 Tuc (Grindlay+, 2001)
J/A+A/391/945 : HST phot. of 74 gal. globular clusters (Piotto+, 2002)
J/ApJ/632/894 : Blue stragglers, HB & turnoff stars (De Marco+, 2005)
J/ApJ/625/796 : X-ray sources in the 47 Tuc GCs (Heinke+, 2005)
J/ApJS/166/249 : Stellar dynamics and PMs in 47Tuc (McLaughlin+, 2006)
J/AJ/132/447 : Surface Brightness of 38 Gal. GCs (Noyola+, 2006)
J/AJ/134/1298 : CaII EWs in 29 Galactic clusters (Carrera+, 2007)
J/A+A/483/183 : Catalogue of Blue Stragglers (Moretti+, 2008)
J/A+A/524/A44 : CN & CH line strengths in 12 globulars (Pancino+, 2010)
J/ApJS/193/23 : Stellar parameters in 47 Tucanae (McDonald+, 2011)
J/ApJS/195/10 : The CDF-S survey: 4Ms source catalogs (Xue+, 2011)
J/ApJ/766/136 : Stellar encounter rates in Gal. GCs (Bahramian+, 2013)
J/MNRAS/434/358 : 4 Gal. globular clusters Fe line depths (Sakari+, 2013)
J/MNRAS/434/1681 : Extremely metal-poor stars CaII triplet (Carrera+, 2013)
J/MNRAS/443/2492 : Δa obs. of 3 globular clusters (Paunzen+, 2014)
J/ApJ/827/12 : HSTPROMO. IV. Blue stragglers (Baldwin+, 2016)
J/A+A/588/A128 : Variables in globular clusters (Figuera Jaimes+, 2016)
J/A+A/601/A96 : Spectroscopy of globular clusters (Larsen+, 2017)
J/A+A/601/A112 : GES iDR4 Mg-Al anticorrelation in GCs (Pancino+, 2017)
J/MNRAS/472/3706 : 47 Tuc GCs Chandra studies (Bhattacharya+, 2017)
J/ApJS/228/2 : CDF-South survey: 7Ms sources (Luo+, 2017)
J/A+A/616/A12 : Gaia DR2 sources in GC and dSph (Gaia Coll.+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ObsID [78/17420] Chandra observation identifier
7-17 A11 "Y/M/D" Date Date of observation (UT)
19-24 A6 --- Arrays Instrument layout for 47 Tuc
26-30 F5.2 ks TimeL [0.85/68.77] Live time
32-38 F7.5 deg RAdeg [5.9/6.1] Telescope optical pointing
right ascension in decimal degrees (J2000)
40-48 F9.5 deg DEdeg [-72.1/-72] Telescope optical pointing
declination in decimal degrees (J2000)
50-54 F5.1 deg Roll Roll angle
56-59 F4.2 s TimeF [0.4/3.3] Frame time of each observation
61-66 F6.3 pix delX [-1.2/0.3] Right ascension shift
68-73 F6.3 pix delY [-0.7/1.2] Declination shift
75-80 F6.3 deg Rot [-0.1/0.3] Rotation angle
82-87 F6.4 --- Scale [0.99/1.01] Scale factor of the wcs_match
transformation matrix
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/537] X-ray catalog sequence number
5- 22 A18 --- Name IAU designation (HHMMSS.ss+DDMMSS.s; J2000)
24- 31 F8.6 deg RAdeg [5.66/6.41] Right Ascension (J2000)
33- 42 F10.6 deg DEdeg [-72.21/-71.9] Declination (J2000)
44- 46 F3.1 arcsec ePos [0/0.8] 1σ positional uncertainty
48- 52 F5.1 arcsec Rp [0.3/448] Projected distance from cluster
center (1)
54- 60 A7 --- PB Binomial no-source probability
62- 68 F7.1 ct NetCts-t [4.6/42882] Full (0.5-8keV) band
aperture-corrected source counts
70- 76 F7.1 ct e_NetCts-t [1.6/42675] 1σ lower bound of NetCts-t
78- 84 F7.1 ct E_NetCts-t [7.5/43092] 1σ upper bound of NetCts-t
86- 92 F7.1 ct NetCts-s [0.3/40761] Soft (0.5-2keV) band
aperture-corrected source counts
94-100 F7.1 ct e_NetCts-s [0/40559] 1σ lower bound of NetCts-s
102-108 F7.1 ct E_NetCts-s [1.9/40965] 1σ upper bound of NetCts-s
110-115 F6.1 ct NetCts-h [-4/8599] Hard (2-8 keV) band
aperture-corrected source counts
117-122 F6.1 ct e_NetCts-h [0/8506]? 1σ lower bound of NetCts-h
124-129 F6.1 ct E_NetCts-h [1/8693] 1σ upper bound of NetCts-h
131-138 E8.2 ph/cm2/s F0.5-8 [4.2e-8/0.00032] Full (0.5-8keV) band photon
flux
140-147 E8.2 ph/cm2/s F0.5-2 [2.1e-9/0.0002] Soft (0.5-2keV) band photon
flux
149-157 E9.2 ph/cm2/s F2-8 [-7.3e-8/7.4e-5] Hard (2-8keV) band photon
flux
159-166 E8.2 10-7W L0.5-8 [2.4e+29/1.8e+33] Absorption-corrected
intrinsic 0.5-8.0keV luminosity in erg/s (2)
168-175 E8.2 10-7W L0.5-2 [7.3e+28/5.4e+32] Absorption-corrected
intrinsic 0.5-2.0keV luminosity in erg/s (2)
177-184 E8.2 10-7W L2-8 [7.9e+28/1.3e+33] Absorption-corrected
intrinsic 2.0-8.0keV luminosity in erg/s (2)
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Note (1): The cluster center coordinates adopted is RA=00:24:05.67 and
DEC=-72:04:52.62, McLaughlin+ (2006, J/ApJS/166/249).
Note (2): X-ray luminosities were derived from the model spectrum, assuming
a distance of 4.02kpc, McLaughlin+ (2006, J/ApJS/166/249).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 18-Nov-2020