J/A+A/464/211 Chandra and near-IR obs. of Cyg OB2 (Albacete Colombo+, 2007)
Unveiling the Cygnus OB2 stellar population with Chandra.
Albacete Colombo J.F., Flaccomio E., Micela G., Sciortino S., Damiani F.
<Astron. Astrophys., 464, 211-227 (2007)>
=2007A&A...464..211A 2007A&A...464..211A
ADC_Keywords: Associations, stellar ; Stars, pre-main sequence ; X-ray sources ;
Photometry, infrared
Keywords: stars: formation - stars: early-type - stars: pre-main-sequence -
X-rays: stars -
Galaxy: open clusters and associations: individual: Cygnus OB2
Abstract:
The aim of this work is to identify the so far unknown low mass
stellar population of the ∼2Myr old Cygnus OB2 star forming region,
and to investigate the X-ray and near-IR stellar properties of its
members. We analyzed a 97.7ks Chandra ACIS-I observation pointed at
the core of the Cygnus OB2 region. Sources were detected using the
PWDETECT code and were positionally correlated with optical and near-
IR catalogs from the literature. Source events were extracted with the
Acis E XTRACT package. X-ray variability was characterized through the
Kolmogorov-Smirnov test and spectra were fitted using absorbed thermal
plasma models. We detected 1003 X-ray sources. Of these, 775 have
near-IR counterparts and are expected to be almost all associated
with Cygnus OB2 members.
Description:
Cygnus OB2 was observed with the ACIS detector on board the Chandra
X-ray Observatory (CXO) on 2004 January 16 (Obs.Id. 4511; PI: E.
Flaccomio).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 133 1003 Cygnus OB2 source catalog
table2.dat 89 1003 Near-IR counterparts of Cygnus OB2 X-ray sources
and near-IR stellar parameters
table3.dat 46 580 X-ray source spectroscopy
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See also:
J/AJ/107/1433 : Cygnus OB2 polarimetry (Kobulnicky+, 1994)
J/ApJS/149/123 : WSRT survey of Cygnus OB2 (Setia Gunawan+, 2003)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- [AFM2007] Sequential number
6- 23 A18 --- CXOCYG Name (HHMMSS.ss+DDMMSS.s)
CXOCYG JHHMMSS.ss+DDMMSS.s in Simbad
25- 26 I2 h RAh Right ascension (J2000)
28- 29 I2 min RAm Right ascension (J2000)
31- 35 F5.2 s RAs Right ascension (J2000)
37 A1 --- DE- Declination sign (J2000)
38- 39 I2 deg DEd Declination (J2000)
41- 42 I2 arcmin DEm Declination (J2000)
44- 48 F5.2 arcsec DEs Declination (J2000)
50- 53 F4.2 arcsec ePos rms uncertainty on position
55- 59 F5.2 arcmin Theta Off-axis angle
61- 66 F6.2 --- Signi Significance of detection
68- 72 I5 pix Area Source extraction area
74- 77 F4.2 --- fPSF [0/1] PSF fraction of source events within
the extraction area, assuming E=1.49keV
79- 83 I5 ct Counts Background-corrected extracted source counts
in the 0.5-8.0keV band (in ct/photon)
85- 91 F7.4 ks ExpTime Exposure time
93- 99 F7.3 ct/ks CRtot Total (0.5-8.0keV) band count rate (1)
101-106 F6.3 ct/ks CRsoft Soft (0.5-1.7keV) band count rate (1)
108-113 F6.3 ct/ks CRmed Medium (1.7-2.8keV) band count rate (1)
115-120 F6.3 ct/ks CRhard Hard (2.8-8.0keV) band count rate (1)
122-125 F4.2 keV Ex Median photon energy
127-131 F5.2 --- Var Logarithm of the KS-test significance,
log(PKS) (2)
133 A1 --- n_Var [+] +: flare-like sources
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Note (1): Count rates computed as the ratio between the source photons
(corrected for fPSF) and the exposure time.
Note (2): Logarithm of the KS-test significance with values ←4 truncated
at that value: sources with log(PKS)←3.0 can be considered almost
definitively variable as we expect at most one of the 1003 sources
(i.e. 0.1%) to be erroneously classified as variable.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- [AFM2007] Sequential number
6- 23 A18 --- CXOAC CXOACJ name (HHMMSS.ss+DDMMSS.s)
25- 40 A16 --- 2MASS 2MASSJ name (HHMMSSss+DDMMSSs)
42- 45 F4.2 arcsec Off ?=- Offset
47- 51 F5.2 mag Jmag ?=- 2MASS J magnitude
53- 56 F4.2 mag e_Jmag ? rms uncertainty on Jmag
58- 62 F5.2 mag Hmag ?=- 2MASS H magnitude
64- 67 F4.2 mag e_Hmag ? rms uncertainty on Hmag
69- 73 F5.2 mag Ksmag ?=- 2MASS Ks magnitude
75- 78 F4.2 mag e_Ksmag ? rms uncertainty on Ksmag
80 A1 --- q_Jmag J band photometric quality flag (1)
81 A1 --- q_Hmag H band photometric quality flag (1)
82 A1 --- q_Ksmag Ks band photometric quality flag (1)
84- 88 F5.2 mag AV ?=- Absorption in V band
89 A1 --- n_AV [n] n indicates stars with unconstrained AV
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Note (1): A to D indicate decreasing quality of the measurements,
U that the value is an upper limit.
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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 --- [AFM2007] Sequential number
6- 10 I5 --- Counts Counts Background subtracted counts in
the spectra
12- 16 F5.2 cm-2 log(NH) Best fit hydrogen column density
18- 21 F4.2 cm-2 e_log(NH) rms uncertainty on log(NH)
23- 26 F4.2 keV kT ?=9.99 Plasma temperature
28- 31 F4.2 keV e_kT ? rms uncertainty on kT
33- 37 F5.2 cm-3 log(EM) Emission measure
39- 42 F4.2 --- chi2 reduced chi2 value for the spectral fit
44- 46 I3 --- dof Degree of freedom for the spectral fit
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 28-Sep-2007