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CYGOB2CXO2 - Cygnus OB2 Association Chandra X-Ray Point Source Catalog 2

HEASARC
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Overview

This table contains a catalog 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. The authors 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 (2MASS), 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 they estimate that their X-ray catalog 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 catalog of 1696 objects presented here includes X-ray broad-band fluxes, spectral model fits, and optical and near-IR photometry in what is one of the largest X-ray catalogs 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.

Catalog Bibcode

2009ApJS..184...84W

References

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        (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in October 2009 based on electronic versions of Tables 2, 3 and 4 from the reference paper which were obtained from the CDS (their catalog J/ApJS/184/84 files table2.dat, table3.dat and table4.dat).

Parameters

Source_Number
A unique sequential identification number for each source in this catalog in order of increasing J2000 Right Ascension.

Alt_Name
The source designation (expected to be) recommended by the Dictionary of Nomenclature of Celestial Objects, using the prefix of '[WD2009]' for Wright and Drake 2009 and the source number.

Name
The standard designation for a Chandra X-ray source using the 'CXOU' prefix and the J2000 equatorial coordinates.

RA
The Right Ascension of the X-ray source in the selected equinox (calculated as the mean background-subtracted event position). This was given in J2000 coordinates to an accuracy of 0.01 seconds of time in the original reference.

Dec
The Declination of the X-ray source in the selected equinox (calculated as the mean background-subtracted event position). This was given in J2000 coordinates to an accuracy of 0.1 arcseconds in the original reference.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Off_Axis
The off-axis angle of the X-ray source from the pointing center, in arcminutes.

Extraction_Area
The area of the X-ray source extraction region, in pixels.

PSF_Fraction
The fraction f_PSF of the point spread function (PSF) that lies within the extraction region for the X-ray source.

SNR
The X-ray source detection significance, in sigma.

Log_Bck_Prob
The logarithm of the Poisson probability that the source is a chance coincidence of background events. Values below -6.0 are listed as -6.00.

Exposure
The full exposure time for the X-ray source (in seconds) derived from the mono-energetic exposure maps for the combined observations.

Median_Energy
The background-corrected median energy of all source photons in the full (0.5 - 8 keV) energy band.

Log_Prob_Constant
The logarithm of the Kolmogorov-Smirnov probability that the source is not variable.

Counts
The net counts for the X-ray source in the full (0.5 - 8 keV) band.

Counts_Pos_Err
The upper (1-sigma) error in the number of net full (0.5 - 8 keV) band counts.

Counts_Neg_Err
The lower (1-sigma) error in the number of net full (0.5 - 8 keV) band counts.

Count_Rate
The net count rate, in ct/s, in the full (0.5 - 8 keV) band.

SB_Count_Rate
The net count rate, in ct/s, in the soft (0.2 - 2 keV) band.

HB_Count_Rate
The net count rate, in ct/s, in the hard (2 - 8 keV) band.

Field_Number
The X-ray source field number (see Section 2 of the reference paper for full details), where the possible values are as follows:

      1 = central field (obsid = 4511)
      2 = north-western field (obsid = 4501)
      3 = overlap region of the two fields
  

Source_Flag
This parameter can contain warning flags with the following possible meanings:

      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 f_PSF < 0.85
  

Spectral_Model
The X-ray spectral model fit type, as follows:

     1T = single-temperature thermal plasma model
  blank = no model fit but quantities determined using methods described
          in Section 2.4 of the reference paper
  

NH_Limit
This parameter is set to '<' if the corresponding Hydrogen column density n_H is an upper limit.

Log_NH
The logarithm of the Hydrogen column density n_H, in atoms/cm2. This parameter is derived either from the spectral model fit or from the observed median energy for unfit sources.

Log_NH_Pos_Err
The upper 90%-confidence interval error in the logarithm of the Hydrogen column density, in atoms/cm2. Uncertainties are missing either when XSPEC was unable to compute them or where they are so large that the parameter is effectively unconstrained.

Log_NH_Neg_Err
The lower 90%-confidence interval error in the logarithm of the Hydrogen column density, in atoms/cm2. Uncertainties are missing either when XSPEC was unable to compute them or where they are so large that the parameter is effectively unconstrained.

APEC_kT_Limit
This parameter is set to '>' if the corresponding model fit thermal plasma temperature kT is a lower limit.

APEC_kT
The absorbed APEC model (0.3 solar abundances) fit thermal plasma temperature kT, in keV

APEC_kT_Pos_Err
The upper 90%-confidence interval error in the model fit thermal plasma temperature kT, in keV. Uncertainties are missing either when XSPEC was unable to compute them or where they are so large that the parameter is effectively unconstrained.

APEC_kT_Neg_Err
The lower 90%-confidence interval error in the model fit thermal plasma temperature kT, in keV. Uncertainties are missing either when XSPEC was unable to compute them or where they are so large that the parameter is effectively unconstrained.

Log_Lx
The logarithm of the X-ray luminosity log L_x in the full (0.5 - 8 keV) band, in erg/s, from the model fit or derived from the number of net counts in the corresponding band for unfit sources (assuming a distance to Cyg OB2 of 1.45 kpc).

Log_Lx_Pos_Err
The upper 90%-confidence interval error in the logarithm of the X-ray luminosity log L_x in the full (0.5 - 8 keV) band, in erg/s. Uncertainties are missing either when XSPEC was unable to compute them or where they are so large that the parameter is effectively unconstrained.

Log_Lx_Neg_Err
The lower 90%-confidence interval error in the logarithm of the X-ray luminosity log L_x in the full (0.5 - 8 keV) band, in erg/s. Uncertainties are missing either when XSPEC was unable to compute them or where they are so large that the parameter is effectively unconstrained.

Log_SB_Lx
The logarithm of the X-ray luminosity in the soft (0.5 - 2 keV) band, in erg/s, from the model fit or derived from the number of net counts in the corresponding band for unfit sources (assuming a distance to Cyg OB2 of 1.45 kpc).

Log_HB_Lx
The logarithm of the X-ray luminosity in the hard (2 - 8 keV) band, in erg/s, from the model fit or derived from the number of net counts in the corresponding band for unfit sources (assuming a distance to Cyg OB2 of 1.45 kpc).

RA_Oir
The Right Ascension of the optical/near-infrared (OIR) source that the X-ray source was matched to, in the selected equinox. This was given in J2000 coordinates to an accuracy of 0.01 seconds of time in the original reference, and was left blank if no association was found.

Dec_Oir
The Declination of the optical/near-infrared (OIR) source that the X-ray source was matched to, in the selected equinox. This was given in J2000 coordinates to an accuracy of 0.1 arcseconds in the original reference, and was left blank if no association was found.

Offset
The offset between the X-ray and the optical/near-infrared source positions, in arcseconds.

Rmag
The INT Photometric H-alpha Survey (IPHAS: Drew et al. 2005, MNRAS, 362, 753) r' band magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Rmag_Error
The error in the IPHAS r' band magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Imag
The INT Photometric H-alpha Survey (IPHAS: Drew et al. 2005, MNRAS, 362, 753) i' band magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Imag_Error
The error in the IPHAS i' band magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Halpha_Mag
The INT Photometric H-alpha Survey (IPHAS: Drew et al. 2005, MNRAS, 362, 753) narrow- band H-alpha magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Halpha_Mag_Error
The error in the IPHAS narrow-band H-alpha magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Jmag
The near-IR J-band magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Jmag_Error
The error in the near-IR J-band magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Hmag
The near-IR H-band magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Hmag_Error
The error in the near-IR H-band magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Ks_Mag
The near-IR K_s-band magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Ks_Mag_Error
The error in the near-IR K_s-band magnitude of the optical/near-infrared (OIR) source to which the X-ray source was matched.

Near_IR_Flags
This parameter contains the origin of the near-IR photometry for the optical/near-infrared (OIR) source to which the X-ray source was matched, for each band (J, H, K_s), respectively, as follows:

   M = 2MASS, CDS Cat. <II/246>
   U = UKIDSS (UKIRT Infrared Deep Sky Survey, Lawrence et al. 2007, MNRAS, 379,
       1599) GPS (Galactic Plane Survey, Lucas et al. 2008, MNRAS, 391, 136)
  

TwoMASS_Flags
The 2MASS photometric quality flags for the J, H, K_s band magnitudes of the optical/near-infrared (OIR) source to which the X-ray source was matched, when they were used.

AFM2007_Source_Number
The corresponding X-ray source number in the catalog of Albacete Colombo et al. (2007, A&A, 464, 211, the HEASARC Browse table CYGOB2CXO).

Spect_Type
The MK spectral type of the optical/near-infrared (OIR) source to which the X-ray source was matched, taken from the literature.

Ref_Spect_Type
The reference code for the MK spectral type of the optical/near-infrared (OIR) source to which the X-ray source was matched, as follows:

             W73 = Walborn (1973, ApJ, 180, 35)
            MT91 = Massey and Thompson (1991, AJ, 101, 1408)
             H99 = Herrero et al. (1999, A&A, 348, 542)
             H03 = Hanson (2003, ApJ, 597, 957)
             K07 = Kiminki et al. (2007, ApJ, 664, 1102)
             N08 = Negueruela et al. (2008, A&A, 487, 575)
  

Opt_Name
The designation for the optical/near-infrared (OIR) source to which the X-ray source was matched, where the following sources are used (NNN or NN is the source number in the corresponding reference):

             [MT91] NNN: Massey and Thompson (1991, AJ, 101, 1408)
             [CPR2002] ANN: Comeron et al. (2002, A&A, 389, 874)
  

Class
The HEASARC Browse object classification, based on the value of the spect_type parameter.


Contact Person

Questions regarding the CYGOB2CXO2 database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 21-Oct-2009