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W40SFRCXO - W 40 Star-Forming Region Chandra X-Ray Point Source Catalog

HEASARC
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Overview

The young stellar cluster illuminating the W40 H II region, one of the nearest massive star-forming regions (SFRs), has been observed with the ACIS detector on board the Chandra X-ray Observatory. Due to its high obscuration, this is a poorly studied stellar cluster with only a handful of bright stars visible in the optical band, including three OB stars identified as primary excitation sources. The authors detect 225 X-ray sources, of which 85% are confidently identified as young stellar members of the region. Two potential distances of the cluster, 260 pc and 600 pc, are used in the paper. Supposing the X-ray luminosity function of SFRs to be universal, it supports a 600 pc distance as a lower limit for W40 and a total population of at least 600 stars down to 0.1 Msun under the assumption of a coeval population with a uniform obscuration. In fact, there is strong spatial variation in Ks-band-excess disk fraction and non-uniform obscuration due to a dust lane that is identified in absorption in optical, infrared, and X-ray. The dust lane is likely part of a ring of material which includes the molecular core within W40. In contrast to the likely ongoing star formation in the dust lane, the molecular core is inactive. The star cluster has a spherical morphology, an isothermal sphere density profile, and mass segregation down to 1.5 Msun. However, other cluster properties, including a <= 1 Myr age estimate and ongoing star formation, indicate that the cluster is not dynamically relaxed. X-ray diffuse emission and a powerful flare from a young stellar object are also reported in the reference paper.

Catalog Bibcode

2010ApJ...725.2485K

References

A Chandra Observation of the Obscured Star-forming Complex W40
    Kuhn M.A., Getman K.V., Feigelson E.D., Reipurth B., Rodney S.A.,
    Garmire G.P.
   <Astrophys. J. Volume 725, Issue 2, pp. 2485-2506 (2010)>.
   =2010ApJ...725.2485K           (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in March 2011 based on electronic versions of Tables, 1, 2 and 4 of the reference paper which were obtained from the ApJ web site.

Parameters

Source_Number
A running source number in order of increasing J2000.0 Right Ascension, which uniquely identifies the X-ray source.

Alt_Name
A HEASARC-created alternative name for the X-ray source using the '[KGF2010]' prefix (for Kuhn, Getman, Feigelson 2010) followed by the source number for the 225 sources in Table 1 of the reference paper, in the style recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

Name
The name of the X-ray source using the 'CXOW40' prefix (for Chandra X-ray Observatory, W40 source) suggested by the authors and the J2000 coordinates of the source in the (higher precision than standard) HHMMSS.ss+DDMMSS.s format.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates and to a precision of 10-6 degrees in the original table.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates and to a precision of 10-6 degrees in the original table.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The estimated standard deviation of the random component of the positional error of the X-ray source, i.e, sqrt(sigmax2 + sigmay2), in arcseconds. The single-axis position errors, sigmax and sigmay, are estimated from the single-axis standard deviations of the point spread function (PSF) inside the extraction region and the number of counts extracted.

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

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

Counts_Error
The average of the upper and lower 1-sigma errors in the net total-band counts for the X-ray source.

Bck_Counts
The background counts expected in the total-band (0.5 - 8 keV) in the X-ray source extraction region

HB_Counts
The net counts extracted in the hard energy band (2 - 8 keV) for the X-ray source.

PSF_Fraction
The fraction of the PSF (at 1.497 keV) enclosed within the extraction region for the X-ray source. Note that a reduced PSF fraction (significantly below 90%) may indicate that the source is in a crowded region.

Significance
The photometric significance of the X-ray source, computed as the net counts divided by the upper error in the net counts.

Source_Anomaly_Flag
This flag parameter indicates the absence/presence of the following source anomalies, using the following codes:

    0: no anomaly
    1: the fractional time that the source was on a detector (FRACEXPO from
       mkarf) is < 0.9
  

Source_Variable_Flag
This flag parameter contains codes which characterize the X-ray source variability in the total band based on the K-S statistic, as follows:

    1: This value is reported for sources with fewer than 4 counts or for
       sources in chip gaps or field edges
    2: no evidence for variability (PKS > 0.05)
    3: possibly variable (0.005 < PKS < 0.05)
    4: definitely variable (PKS < 0.005)
  

Exposure
The effective exposure time for the X-ray source, in seconds (s). (This was converted by the HEASARC from the units of ks given in the original reference table). This is the approximate time that the source would have to be observed at the aimpoint of the ACIS-I detector in Chandra Cycle 8 in order to obtain the reported number of net source counts.

TwoMASS_Name
The designation of the 2MASS counterpart to the X-ray source.

CXO_2MASS_Offset
The angular offset between the X-ray source and 2MASS object positions, in arcseconds.

Jmag
The 2MASS J-band magnitude J of the near-IR counterpart to the X-ray source.

Jmag_Error
The uncertainty in the 2MASS J-band magnitude of the near-IR counterpart to the X-ray source.

Hmag
The 2MASS H-band magnitude H of the near-IR counterpart to the X-ray source.

Hmag_Error
The uncertainty in the 2MASS H-band magnitude of the near-IR counterpart to the X-ray source.

Ks_Mag
The 2MASS Ks-band magnitude Ks of the near-IR counterpart to the X-ray source.

Ks_Mag_Error
The uncertainty in the 2MASS Ks-band magnitude of the near-IR counterpart to the X-ray source.

TwoMASS_Flags
The 2MASS photometric quality and confusion flag values for the likely 2MASS counterpart to the X-ray source, as defined in the Explanatory Supplement to the 2MASS All Sky Data Release at http://www.ipac.caltech.edu/2mass/releases/allsky/doc/sec2_2a.html.

Membership_Class
The membership class flag for the object as follows:

      W40-noKs = W40 stars without Ks-excess
        W40-Ks = W40 stars with Ks-excess
           W40 = W40 stars with no Ks-excess classification
           FRG = foreground stars
            EG = Extragalactic sources
  

Av
The visual absorption AV, in magnitudes, of the near-IR counterpart derived from its position in the J vs. J-H Diagram and assuming a distance of 600 pc and an age of 1 Myr.

Stellar_Mass
The stellar mass, in solar masses, of the near-IR counterpart derived from its position in the J vs. J-H Diagram and assuming a distance of 600 pc and an age of 1 Myr.

Stellar_Mass_Error
The uncertainty in the stellar mass, in solar masses.

Ukirt_Flag
This flag parameter details the source information that the authors obtained in JHK images of the central part of the cluster using UKIRT, as follows:

      0 = no source
      1 = single source present
      2 = outside Field of View
      3 = double source present
  

VLA_ID
The identification of the counterpart VLA source in the paper of Rodriguez et al. (2010, AJ, 140, 968).

Median_Energy
The background-corrected total-band median photon energy of the X-ray source photons, in keV.

Log_HB_Lx_Obs
The logarithm of the observed hard-band (2 - 8 keV) luminosity of the X-ray source, assuming a distance of 600 pc, in erg/s, inferred from XSPEC fitting of the observed X-ray spectrum.

Log_Lx_Obs
The logarithm of the observed total-band (0.5 - 8 keV) luminosity of the X-ray source, assuming a distance of 600 pc, in erg/s, inferred from XSPEC fitting of the observed X-ray spectrum.

APEC_kT
The best-fit value of the plasma temperature from the APEC model, kT, in keV. All such fits used the ``wabs(apec)'' model in XSPEC and assumed 0.3 solar abundances previously suggested as typical of YSOs in SFRs.

Log_NH_1
The logarithm of the best-fit column density, log nH, in H atoms/cm2, inferred from XSPEC fitting of the observed X-ray spectrum.

Log_HB_Lx_1
The logarithm of the intrinsic (absorption-corrected) hard-band (2 - 8 keV) luminosity of the X-ray source assuming a distance of 600 pc, in erg/s, inferred from XSPEC fitting of the observed X-ray spectrum.

Log_Lx_1
The logarithm of the intrinsic (absorption-corrected) total-band (0.5 - 8 keV) luminosity of the X-ray source assuming a distance of 600 pc, in erg/s, inferred from XSPEC fitting of the observed X-ray spectrum.

Log_NH_2
The logarithm of the best-fit column density, log nH, in H atoms/cm2, inferred from XPHOT. XPHOT (Getman et al. 2010, ApJ, 708, 1760) is a non-parametric method for estimation of apparent and intrinsic broadband fluxes of and absorbing X-ray column densities towards X-ray sources.

Log_NH_2_Error
The uncertainty in the best-fit column density, log nH, in H atoms/cm2, inferred from XPHOT. This is the sum in quadrature of the systematic and statistical errors.

Log_HB_Lx_2
The logarithm of the intrinsic (absorption-corrected) hard-band (2 - 8 keV) luminosity of the X-ray source assuming a distance of 600 pc, in erg/s, inferred from XPHOT.

Log_HB_Lx_2_Error
The uncertainty in the intrinsic (absorption-corrected) hard-band (2 - 8 keV) luminosity of the X-ray source assuming a distance of 600 pc, in erg/s, inferred from XPHOT. This is the sum in quadrature of the systematic and statistical errors.

Log_Lx_2
The logarithm of the intrinsic (absorption-corrected) total-band (0.5 - 8 keV) luminosity of the X-ray source assuming a distance of 600 pc, in erg/s, inferred from XPHOT.

Log_Lx_2_Error
The uncertainty in the intrinsic (absorption-corrected) total-band (0.5 - 8 keV) luminosity of the X-ray source assuming a distance of 600 pc, in erg/s, inferred from XPHOT. This is the sum in quadrature of the systematic and statistical errors.


Contact Person

Questions regarding the W40SFRCXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 28-Aug-2012