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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
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:

       FileName      Lrecl  Records   Explanations

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


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

   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

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.


Byte-by-byte Description of file: table2.dat

   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

Note (1): A to D indicate decreasing quality of the measurements,
     U that the value is an upper limit.


Byte-by-byte Description of file: table3.dat

   Bytes Format Units   Label     Explanations

   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


History:
    From electronic version of the journal
(End)                                      Patricia Vannier [CDS]    28-Sep-2007