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M17CXO - M 17 Chandra X-Ray Point Source Catalog |
HEASARC Archive |
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 erg s-1 < log LX < 32.8 erg 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 AV > 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 LX ~ 10-7 Lbol. 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..353BReferences
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,
(sigmax2 + sigmay2)0.5, in arcseconds. The single-axis position
errors, sigmax and sigmay, 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 PB (log_bck_prob) is an upper limit.
Log_Bck_Prob
The log of the probability (log PB) that the extracted counts (total band)
are solely from the background. Some sources have PB 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 PB < 0.003 (0.3%) are considered primary sources
(source_flag = 'P'), while those with 0.003 (0.3%) < PB < 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 based 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 (PKS > 0.05) b: possibly variable (0.005 < PKS < 0.05) c: definitely variable (PKS < 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 NH, in H
atoms cm-2. 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 cm-2.
Log_NH_Pos_Err
The upper 90% confidence level error in the best-fit value of log NH, in H
atoms cm-2. 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 NH > 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 PLNorm.
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 PLNorm.
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 PB that the X-ray source was a background
fluctuation rather than a 'real' source when defining their final source
list: PB < 0.003 for the primary sources and 0.003 < PB < 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: Thursday, 19-Mar-2015 21:09:08 EDT
- HEASARC Director: Dr. Andy Ptak
- NASA Official: Dr. Andy Ptak
- Web Curator: J.D. Myers
- Last Modified: 19-Mar-2015