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M17CXO - M 17 Chandra X-Ray Point Source Catalog

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Overview

This table contains some of the results from a Chandra ACIS observation of the stellar populations in and around the M17 H II region. The field reveals 886 sources (listed in the present table) with observed X-ray luminosities (uncorrected for absorption) between ~ 29.3 ergs s-1 < log L_X < 32.8 ergs s-1, 771 of which have stellar counterparts in infrared images. Spectral analysis results for the 598 brightest X-ray sources which have photometric significance of 2.0 or greater) are also given herein. For 546 of the X-ray sources, the fits used the "wabs(apec)" thermal plasma model in XSPEC assuming scaled 0.3 times solar photospheric abundances, while for the other 52 X-ray sources for which either the thermal model poorly described the data or required nonphysical parameters and the X-ray source was not identified with a known stellar counterpart, the fits used the "wabs(powerlaw)" model in XSPEC.

In addition to the comprehensive tabulation of X-ray source properties, several other results were presented in the reference paper:

1. The X-ray luminosity function is calibrated to that of the Orion Nebula Cluster population to infer a total population of roughly 8000-10,000 stars in M17, one-third lying in the central NGC 6618 cluster.

2. About 40% of the ACIS sources are heavily obscured with A_V > 10 mag. Some are concentrated around well-studied star-forming regions -- IRS 5/UC1, the Kleinmann-Wright Object, and M17-North -- but most are distributed across the field. As previously shown, star formation appears to be widely distributed in the molecular clouds. X-ray emission is detected from 64 of the hundreds of Class I protostar candidates that can be identified by near- and mid-infrared colors. These constitute the most likely protostar candidates known in M17.

3. The spatial distribution of X-ray stars is complex: in addition to the central NGC 6618 cluster and well-known embedded groups, we find a new embedded cluster (designated M17-X), a 2 pc long arc of young stars along the southwest edge of the M17 H II region, and 0.1 pc substructure within various populations. These structures may indicate that the populations are dynamically young.

4. All (14/14) of the known O stars but only about half (19/34) of the known B0-B3 stars in the M17 field are detected. These stars exhibit the long-reported correlation between X-ray and bolometric luminosities of L_X ~ 10^-7L_bol. While many O and early-B stars show the soft X-ray emission expected from microshocks in their winds or moderately hard emission that could be caused by magnetically channeled wind shocks, six of these stars exhibit very hard thermal plasma components (kT > 4 keV) that may be due to colliding wind binaries. More than 100 candidate new OB stars are found, including 28 X-ray detected intermediate- and high-mass protostar candidates with infrared excesses.

5. Only a small fraction (perhaps 10%) of X-ray selected high- and intermediate-mass stars exhibit K-band-emitting protoplanetary disks, providing further evidence that inner disks evolve very rapidly around more massive stars.


Catalog Bibcode

2007ApJS..169..353B

References

The young stellar population in M17 revealed by Chandra
    Broos P.S., Feigelson E.D., Townsley L.K., Getman K.V., Wang J.,
    Garmire G.P., Jiang Z., Tsuboi Y.
    <Astrophys. J. Suppl. 169, 353 (2007)>
    =2007ApJS..169..353B      (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in December 2007 based on electronic versions of Tables 1, 2, 3, 4 and 5 of the reference paper which were obtained from the electronic 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
An alternative name for the X-ray source using the '[BFT2007]' prefix followed by the source number, as recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

Name
The name of the X-ray source using the 'CXOU' prefix (for Chandra X-ray Observatory, Unregistered source) 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 statistical positional error of the X-ray source, i.e., the estimated standard deviation of the random component of the position error, (sigma_x2 + sigma_y2)0.5, in arcseconds. The single-axis position errors, sigma_x and sigma_y, are estimated from the single-axis standard deviations of the 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 (the position of Kleinmann's Anonymous Star, the source with the earliest spectral type in the central ring of O stars in NGC 6618), 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 total-band counts.

Bck_Counts
The background counts 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 net counts divided by upper error in the net counts.

Log_Bck_Prob_Limit
This flag parameter is set to '<' if the corresponding value of log P_B (log_bck_prob) is an upper limit.

Log_Bck_Prob
The log of the probability (log P_B) that the extracted counts (total band) are solely from the background. Some sources have P_B values above the 1% threshold that defines the catalog because local background estimates can rise during the final extraction iteration after sources are removed from the catalog. Sources with P_B < 0.003 (0.3%) are considered primary sources (source_flag = 'P'), while those with 0.003 (0.3%) < P_B < 0.01 (1%) are considered tentative (source_flag = 'T').

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

  g: fractional time that source was on a detector (FRACEXPO from mkarf) is <0.9
  e: source on field edge
  p: source piled up
  s: source on readout streak
  

Source_Variable_Flag
This flag parameter contains codes which characterize the X-ray source variability in the total (2 - 8 keV) band basd on the K-S statistic, as follows (no value is reported for sources with fewer than four counts or for sources in chip gaps or on field edges):

  a: no evidence for variability (P_KS > 0.05)
  b: possibly variable (0.005 < P_KS < 0.05)
  c: definitely variable (P_KS < 0.005)
  

Exposure
The effective exposure time for the X-ray source, in seconds. This is the approximate time the source would have to be observed on-axis (i.e., no telescope vignetting) on a nominal region of the detector (with no dithering over insensitive regions of the detector) in order to obtain the reported number of source counts.

Median_Energy
The background-corrected total-band (0.5 - 8 keV) median photon energy for the X-ray source, in keV.

Log_NH_Neg_Err
The lower 90% confidence level error in the best-fit value of log n_H, in H atoms/cm2. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; the listed parameter values are unreliable.

Log_NH
The logarithm of the best-fit column density, in H atoms/cm2.

Log_NH_Pos_Err
The upper 90% confidence level error in the best-fit value of log n_H, in H atoms/cm2. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; the listed parameter values are unreliable.

Log_NH_Flag
If this flag parameter is marked with a value of 'e', this indicates that the corresponding parameter value was frozen in the fit.

APEC_kT_Neg_Err
The lower 90% confidence level error in the best-fit value of the plasma temperature from the APEC model, kT, in keV. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; the listed parameter values are unreliable.

APEC_kT
The best-fit value of the plasma temperature from the APEC model, kT, in keV.

APEC_kT_Pos_Err
The upper 90% confidence level error in the best-fit value of the plasma temperature from the APEC model, kT, in keV. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; the listed parameter values are unreliable.

APEC_kT_Flag
If this flag parameter is marked with a value of 'e', this indicates that the corresponding parameter value was frozen in the fit.

Log_EM_Neg_Err
The lower 90% confidence level error in the best-fit value of the logarithm of the model emission measure, log EM, in cm-3. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; the listed parameter values are unreliable.

Log_EM
The logarithm of the model emission measure assuming a distance of 1.6 kpc, in cm-3.

Log_EM_Pos_Err
The upper 90% confidence level error in the best-fit value of the logarithm of the model emission measure, log EM, in cm-3. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; the listed parameter values are unreliable.

Log_SB_Lx_Obs
The logarithm of the observed soft-band (0.5 - 2 keV) luminosity of the X-ray source assuming a distance of 1.6 kpc, in erg/s (omitted when log n_H > 22.5 cm-2, since the soft-band emission is essentially unmeasurable in such cases).

Log_HB_Lx_Obs
The logarithm of the observed hard-band (2 - 8 keV) luminosity of the X-ray source assuming a distance of 1.6 kpc, in erg/s.

Log_HB_Lx
The logarithm of the absorption-corrected hard-band (2 - 8 keV) Luminosity of the X-ray source assuming a distance of 1.6 kpc, in erg/s.

Log_Lx_Obs
The logarithm of the observed total-band (0.5 - 8 keV) luminosity of the X-ray source assuming a distance of 1.6 kpc, in erg/s.

Log_Lx
The logarithm of the absorption-corrected total-band (0.5 - 8 keV) luminosity of the X-ray source assuming a distance of 1.6 kpc, in erg/s.

Spectral_Flag
If this flag parameter is marked with an initial value of '2T', this indicates that a two-temperature APEC model was used, the second temperature of which is given in parentheses, e.g., '2T (0.9 keV)'.

Spectral_Index_Neg_Err
The lower 90% confidence level error in the best-fit value of the power-law photon index, Gamma. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; the listed parameter values are unreliable.

Spectral_Index
The best-fit value of the power-law photon index, Gamma.

Spectral_Index_Pos_Err
The upper 90% confidence level error in the best-fit value of the power-law photon index, Gamma. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; the listed parameter values are unreliable.

Log_PL_Norm_Neg_Err
The lower 90% confidence level error in the best-fit value of the logarithm of the power-law normalization, log PL_Norm. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; the listed parameter values are unreliable.

Log_PL_Norm
The logarithm of the power-law normalization of the best-fit model, log PL_Norm.

Log_PL_Norm_Pos_Err
The upper 90% confidence level error in the best-fit value of the logarithm of the power-law normalization, log PL_Norm. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; the listed parameter values are unreliable.

Cen_Number
The source number of the likely optical star counterpart to the X-ray source from Chini, Elsaesser & Neckel (CEN; 1980, A&A, 91, 186).

Spect_Type
The spectral type of the likely optical star counterpart to the X-ray source. Spectral types with a corresponding spect_type_flag value of 'H' come from Hanson et al. (1997, ApJ, 489, 698), while the others come from SIMBAD, else Chini et al. (1980, A&A, 91, 186).

Spect_Type_Flag
This flag parameter has a value of 'H' if the corresponding spectral type comes from Hanson et al. (1997, ApJ, 489, 698).

Hhc_Number
The source number of the likely near-infrared counterpart to the X-ray source, from Hanson, Howarth & Conti (1997, ApJ, 489, 698) derived from Bumgardner (1992, MS thesis). A reference frame offset of 1.9 arcseconds between the ACIS and Hanson et al. (1997) positions was removed before matching the catalogs.

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

TwoMASS_Flags
The 2MASS source Contamination and Confusion Flag value 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.

Sirius_Number
The running sequence number from the SIRIUS Catalog for the likely SIRIUS counterpart to the X-ray source, from Jiang et al. (2002, ApJ, 577, 245).

Sirius_Number_Flag
This flag parameter is set to 'a' to indicate that the X-ray source position lay outside of the SIRIUS field of view.

Glimpse_Name
The GLIMPSE (a Spitzer legacy science program) designation of the likely infrared counterpart to the X-ray source. Sources are taken from the Highly Reliable Catalog, ver. 1 at http://www.astro.wisc.edu/sirtf/glimpsedata.html.

IR_Match_Flags
This parameter contains match ambiguity flags. An 's' in the first/second/third position indicates there are 'secondary' (i.e., multiple) matches with the 2MASS/SIRIUS/GLIMPSE catalog, respectively.

Ref_IR_Match
This parameter purportedly contains a code which indicates additional notes in the documentation on matches to other catalogs. In fact, if populated, it contains the same number as the X-ray source number, except in 2 cases where it contains the source number of a very nearby X-ray source, so the significance of this parameter is unclear to the HEASARC.

Jmag_Limit
If the corresponding magnitude of the IR counterpart is an upper limit to the flux (lower limit to the magnitude) rather than a measured value, this parameter is set to '>'.

Jmag
The J-band magnitude of the likely infrared counterpart to the X-ray source. Values are generally taken from SIRIUS when a match is identified, or from 2MASS otherwise. However, the bright sources 366, 701, 720, and 854 suffer saturation in the SIRIUS photometry so the 2MASS values are reported instead. Magnitudes have been corrected to the CIT photometry system (Elias et al. 1982, AJ, 87, 1029). 2MASS magnitudes have the corresponding limit parameter set to '>' when the 2MASS Photometric Quality Flag indicates a flux upper limit (flag = U) and are omitted when the flag indicates poor photometry (flag = E).

Jmag_Flag
A value of ':' for this flag parameter indicates that the reported photometry errors for the corresponding IR magnitude exceed 0.1 mag.

Hmag_Limit
If the corresponding magnitude of the IR counterpart is an upper limit to the flux (lower limit to the magnitude) rather than a measured value, this parameter is set to '>'.

Hmag
The H-band magnitude of the likely infrared counterpart to the X-ray source. Values are generally taken from SIRIUS when a match is identified, or from 2MASS otherwise. However, the bright sources 366, 701, 720, and 854 suffer saturation in the SIRIUS photometry so the 2MASS values are reported instead. Magnitudes have been corrected to the CIT photometry system (Elias et al. 1982, AJ, 87, 1029). 2MASS magnitudes have the corresponding limit parameter set to '>' when the 2MASS Photometric Quality Flag indicates a flux upper limit (flag = U) and are omitted when the flag indicates poor photometry (flag = E).

Hmag_Flag
A value of ':' for this flag parameter indicates that the reported photometry errors for the corresponding IR magnitude exceed 0.1 mag.

Kmag_Limit
If the corresponding magnitude of the IR counterpart is an upper limit to the flux (lower limit to the magnitude) rather than a measured value, this parameter is set to '>'.

Kmag
The K-band magnitude of the likely infrared counterpart to the X-ray source. Values are generally taken from SIRIUS when a match is identified, or from 2MASS otherwise. However, the bright sources 366, 701, 720, and 854 suffer saturation in the SIRIUS photometry so the 2MASS values are reported instead. Magnitudes have been corrected to the CIT photometry system (Elias et al. 1982, AJ, 87, 1029). 2MASS magnitudes have the corresponding limit parameter set to '>' when the 2MASS Photometric Quality Flag indicates a flux upper limit (flag = U) and are omitted when the flag indicates poor photometry (flag = E).

Kmag_Flag
A value of ':' for this flag parameter indicates that the reported photometry errors for the corresponding IR magnitude exceed 0.1 mag.

IRAC_3p6_um_Mag
The GLIMPSE 3.6-micron-band magnitude of the likely infrared counterpart to the X-ray source. The median photometric error for the reported counterparts in this band is 0.13 mag, and the maximum error in this band is 0.34 mag.

IRAC_4p5_um_Mag
The GLIMPSE 4.5-micron-band magnitude of the likely infrared counterpart to the X-ray source. The median photometric error for the reported counterparts in this band is 0.12 mag, and the maximum error in this band is 0.32 mag.

IRAC_5p8_um_Mag
The GLIMPSE 5.8-micron-band magnitude of the likely infrared counterpart to the X-ray source. The median photometric error for the reported counterparts in this band is 0.16 mag, and the maximum error in this band is 0.34 mag.

IRAC_8p0_um_Mag
The GLIMPSE 8.0-micron-band magnitude of the likely infrared counterpart to the X-ray source. The median photometric error for the reported counterparts in this band is 0.16 mag, and the maximum error in this band is 0.35 mag.

Source_Flag
This flag parameter (created by the HEASARC) is set to 'P' to indicate the specified source is one of the 845 sources from the Primary Chandra M17 Catalog listed in Table 1 of the reference paper, or to 'T' to indicate the specified source is one of the 41 sources from the Tentative Chandra M17 Catalog listed in Table 2 of the reference paper. The authors chose two thresholds on the probability P_B that the X-ray source was a background fluctuation rather than a 'real' source when defining their final source list: P_B < 0.003 for the primary sources and 0.003 < P_B < 0.01 for the tentative sources. Counterparts were identified for 31 of the tentative sources (see Section 2.4 of the reference paper), adding confidence that these sources are real.


Contact Person

Questions regarding the M17CXO database table can be addressed to the HEASARC User Hotline.

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