J/ApJS/184/84 X-ray sources in Cyg OB2 region (Wright+, 2009)
The Massive Star Forming Region Cygnus OB2.
I. Chandra Catalog of Association Members
Wright N.J., Drake J.J.
<Astrophys. J. Suppl. Ser. 184, 84 (2009)>
=2009ApJS..184...84W 2009ApJS..184...84W
ADC_Keywords: Associations, stellar ; Stars, early-type ; X-ray sources ;
Photometry, infrared
Keywords: open clusters and associations: individual: Cygnus OB2 -
stars: pre-main sequence - X-rays: stars
Abstract:
We present a catalogue of 1696 X-ray sources detected in the massive
star forming region (SFR) Cygnus OB2 and extracted from two archival
Chandra observations of the center of the region. A deep source
extraction routine, exploiting the low background rates of Chandra
observations was employed to maximize the number of sources extracted.
Observations at other wavelengths were used to identify low count-rate
sources and remove likely spurious sources. Monte Carlo simulations
were also used to assess the authenticity of these sources. X-ray
spectra were fitted with thermal plasma models to characterize the
objects and X-ray light curves were analyzed to determine their
variability. We used a Bayesian technique to identify optical or
near-IR counterparts for 1501 (89%) of our sources, using deep
observations from the INT Photometric H-alpha Survey, the Two Micron
All Sky Survey, and the UKIRT Infrared Deep Sky Survey-Galactic plane
Survey. 755 (45%) of these objects have six-band r', H-alpha, i', J,
H, and K optical and near-IR photometry. From an analysis of the
Poisson false-source probabilities for each source we estimate that
our X-ray catalogue includes <1% of false sources, and an even lower
fraction when only sources with optical or near-IR associations are
considered. A Monte Carlo simulation of the Bayesian matching scheme
allows this method to be compared to more simplified matching
techniques and enables the various sources of error to be quantified.
The catalogue of 1696 objects presented here includes X-ray broad band
fluxes, model fits, and optical and near-IR photometry in what is one
of the largest X-ray catalogue of a single SFR to date. The high
number of stellar X-ray sources detected from relatively shallow
observations confirms the status and importance of Cygnus OB2 as one
of our Galaxy's most massive SFRs.
Description:
X-ray detections, broad-band fluxes, mean energies, X-ray spectral
fits, optical and near-IR photometry for 1696 stellar X-ray sources
in the Cygnus OB2 association.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 124 1696 X-ray detections and broad-band photometry
table3.dat 79 1696 X-ray spectral fits for sources
table4.dat 153 1696 Optical and near-IR photometry of sources
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See also:
J/AJ/101/1408 : Massive stars in Cyg OB2 (Massey+ 1991)
J/ApJ/664/102 : Radial velocity survey of Cyg OB2 association (Kiminki+, 2007)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq Running identification number
6- 7 I2 h RAh Hour of Right Ascension (J2000) (1)
9- 10 I2 min RAm Minute of Right Ascension (J2000) (1)
12- 16 F5.2 s RAs Second of Right Ascension (J2000) (1)
18 A1 --- DE- Sign of Declination (J2000) (1)
19- 20 I2 deg DEd Degree of Declination (J2000) (1)
22- 23 I2 arcmin DEm Arcminute of Declination (J2000) (1)
25- 28 F4.1 arcsec DEs Arcsecond of Declination (J2000) (1)
30- 33 F4.2 arcmin theta Off-axis angle
35- 38 I4 pix Area Source extraction region area
40- 43 F4.2 --- fPSF Point Spread Function fraction in
extraction region
45- 51 F7.2 --- Sig Source detection significance
53- 57 F5.2 [-] lgPco Poisson probability log of a coincidence (2)
59- 64 F6.2 ks Exp Full exposure time (3)
66- 69 F4.2 keV Ex 0.5-8keV median energy (4)
71- 75 F5.2 [-] lgPks Log Kolmogorov-Smirnov probability (5)
77- 84 F8.2 ct Cnts Net 0.5-8keV band counts
86- 90 F5.1 ct E_Cnts Upper 1σ error on Cnts
92- 96 F5.1 ct e_Cnts Lower 1σ error on Cnts
98-104 F7.3 ct/ks Full Net 0.5-8keV band count rate
106-112 F7.3 ct/ks Soft Net 0.2-2keV band count rate
114-120 F7.3 ct/ks Hard Net 2-8keV band count rate
122 I1 --- Fld [1/3] Source field number (6)
124 A1 --- Flg [EN] Warning detection flag (7)
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Note (1): Calculated as the mean background subtracted event position.
Note (2): Probability hhat the source is a chance coincidence of background
events. Values below -6.0 are listed as -6.00.
Note (3): Derived from the mono-energetic exposure maps for the
combined observations.
Note (4): Background corrected.
Note (5): That the source is not variable.
Note (6): Source field number is:
1 = central field;
2 = north-western field;
3 = overlap region
Note (7): Warning flag as follows:
E = the source lies in or on a chip gap or at the edge of the chip
N = the source is very close to another source, such that fPSF<0.85
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq Running identification number
6- 13 F8.2 ct Cnts Net 0.5-8keV band counts
15- 17 A3 --- Mfit Model fit type (1)
18 A1 --- l_logNH Limit flag on logNH
19- 23 F5.2 [cm-2] logNH ? log of Hydrogen column density (2)
25- 28 F4.2 [cm-2] E_logNH ? Upper 90% confidence interval in logNH (3)
30- 33 F4.2 [cm-2] e_logNH ? Lower 90% confidence interval in logNH (3)
35 A1 --- l_kT Limit flag on kT
36- 41 F6.2 keV kT ? Model fit thermal plasma temperature
43- 46 F4.2 keV E_kT ? Upper 90% confidence interval in kT (3)
48- 51 F4.2 keV e_kT ? Lower 90% confidence interval in kT (3)
53- 57 F5.2 [10-7W] logL log 0.5-8keV band luminosity (4)
59- 62 F4.2 [10-7W] E_logL ? Upper 90% confidence interval in logL (3)
64- 67 F4.2 [10-7W] e_logL ? Lower 90% confidence interval in logL (3)
69- 73 F5.2 [10-7W] logLs ? Log 0.5-2keV band luminosity (4)
75- 79 F5.2 [10-7W] logLh ? Log 2-8keV band luminosity (4)
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Note (1): Model fit type is "1T" for single-temperature thermal plasma
model; otherwise (blank field) the quantities are determined using
methods described in Section 2.4
Note (2): From model fit or from the median energy for unfit sources.
Note (3): Uncertainties are missing either when XSPEC was unable to compute
them or where they are so large that the parameter is effectively
unconstrained.
Note (4): From model fit or derived from the number of net counts for unfit
sources (assuming a distance of 1.45kpc). In units of erg/s.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Seq Running identification number
6- 7 I2 h RAh ? Hour of Right Ascension (J2000) (1)
9- 10 I2 min RAm ? Minute of Right Ascension (J2000) (1)
12- 16 F5.2 s RAs ? Second of Right Ascension (J2000) (1)
17 A1 --- DE- ? Declination sign (1)
18- 19 I2 deg DEd ? Degree of Declination (J2000) (1)
21- 22 I2 arcmin DEm ? Arcminute of Declination (J2000) (1)
24- 27 F4.1 arcsec DEs ? Arcsecond of Declination (J2000) (1)
29- 34 F6.3 arcsec Off ? X-ray and optical/NIR position offset
36- 40 F5.2 mag r'mag ? IPHAS r' band magnitude
42- 46 F5.3 mag e_r'mag ? Error in r'mag
48- 52 F5.2 mag i'mag ? IPHAS i' band magnitude
54- 58 F5.3 mag e_i'mag ? Error in i'mag
60- 64 F5.2 mag Hamag ? IPHAS Hα band magnitude
66- 70 F5.3 mag e_Hamag ? Error in Hamag
72- 76 F5.2 mag Jmag ? J band magnitude
78- 82 F5.3 mag e_Jmag ? Error in Jmag
84- 88 F5.2 mag Hmag ? J band magnitude
90- 94 F5.3 mag e_Hmag ? Error in Hmag
96-100 F5.2 mag Ksmag ? Ks band magnitude
102-106 F5.3 mag e_Ksmag ? Error in Kmag
108-110 A3 --- NIR Near-IR photometry source (2)
113-115 A3 --- 2Mq 2MASS IJKs photometry quality flags
118-121 I4 --- [AFM2007] ? Number in Albacete Colombo et al. 2007
(Cat. J/A+A/464/211)
124-130 A7 --- SpT Literature MK spectral type
132-139 A8 --- r_SpT Reference for Sptype (3)
141-153 A13 --- OName Other name (4)
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Note (1): Position of OIR source that X-ray source was matched to
(blank if no association found).
Note (2): Near-IR photometry source is
M = 2MASS, Cat. II/246;
U = UKIDSS
Note (3): References as follows:
W73 = Walborn (1973ApJ...180L..35W 1973ApJ...180L..35W)
MT91 = Massey and Thompson (1991, Cat. J/AJ/101/1408)
H99 = Herrero et al. (1999A&A...348..542H 1999A&A...348..542H)
H03 = Hanson (2003ApJ...597..957H 2003ApJ...597..957H)
K07 = Kiminki et al. (2007, Cat. J/ApJ/664/1102)
N08 = Negueruela et al. (2008A&A...487..575N 2008A&A...487..575N)
Note (4): Source numbers in:
[MT91] NNN: Massey and Thompson (1991, Cat. J/AJ/101/1408)
[CPR2002] ANN: Comeron et al. (2002A&A...389..874C 2002A&A...389..874C)
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Acknowledgements:
N. Wright, nwright(at)head.cfa.harvard.edu
(End) Patricia Vannier [CDS] 11-Sep-2009