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CARINACLAS - Carina Nebula Chandra X-Ray Point Source Classes

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Overview

The Chandra Carina Complex Project (CCCP) provides a sensitive X-ray survey of a nearby starburst region over > 1 deg2 in extent. Thousands of faint X-ray sources are found, many concentrated into rich young stellar clusters. However, significant contamination from unrelated Galactic and extragalactic sources is present in the X-ray catalog. In their paper, the authors describe the use of a naive Bayes classifier to assign membership probabilities to individual sources, based on source location, X-ray properties, and visual/infrared properties. For the particular membership decision rule adopted, 75% of CCCP sources are classified as members, 11% are classified as contaminants, and 14% remain unclassified. The resulting sample of stars likely to be Carina members is used in several other studies, which appear in the special issue of Astrophysical Journal Supplement (Volume 194, May 2011 Issue) which was devoted to the CCCP.

Catalog Bibcode

2011ApJS..194....4B

References

A Naive Bayes Source Classifier for X-ray Sources
        Broos P.S., Getman K.V., Povich M.S., Townsley L.K., Feigelson E.D.,
        Garmire G.P.
       <Astrophys. J. Suppl. Ser., 194, 4 (2011)>
       =2011ApJS..194....4B

Provenance

This table was created by the HEASARC in June 2011 based on the electronic version of Table 5 from the reference paper which was obtained from the ApJS web site. In the input source table, the names were truncated by 3 characters from their complete version. The HEASARC corrected these names, and also obtained the Chandra source positions, using the electronic version of Table 2 from the companion paper (Broos et al. 2011, ApJS, 194, 2: available as the HEASARC Browse table CARINACXO), also obtained from the ApJS web site.

Parameters

Name
The source designation registered with the CDS Dictionary of Nomenclature of Celestial Objects, using the prefix of 'CXONGC' for 'Chandra X-ray Observatory Great Nebula in Carina' and the J2000.0 equatorial coordinates truncated to 0.01 seconds of time and 0.1 arcseconds, e.g., 'CXOGNC J103090.94-594714.5'.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates to an accuracy of 10-6 degrees (0.0036 arcseconds) in Broos et al. (2011, ApJS, 194, 2: available as the HEASARC Browse table CARINACXO).

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates to an accuracy of 10-6 degrees (0.0036 arcseconds) in Broos et al. (2011, ApJS, 194, 2: available as the HEASARC Browse table CARINACXO).

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

H1_SP_Prob
The 'spatial prior class probability' that the specific source is a foreground Galactic field star (the H1 hypothesis), based on the local density of detected sources and on the local densities of expected contaminants. See Section 3.2 of the reference paper for more details.

H2_SP_Prob
The 'spatial prior class probability' that the specific source is a young star in the Carina complex (the H2 hypothesis), based on the local density of detected sources and on the local densities of expected contaminants. See Section 3.2 of the reference paper for more details.

H3_SP_Prob
The 'spatial prior class probability' that the specific source is a background Galactic field star (the H3 hypothesis), based on the local density of detected sources and on the local densities of expected contaminants. See Section 3.2 of the reference paper for more details.

H4_SP_Prob
The 'spatial prior class probability' that the specific source is an extragalactic source (the H4 hypothesis), based on the local density of detected sources and on the local densities of expected contaminants. See Section 3.2 of the reference paper for more details.

H1_Post_Prob
The 'posterior class probability' that the specific source is a foreground Galactic field star (the H1 hypothesis), based on a naive Bayes classifier using 8 observed or physical source properties: the median X-ray energy, the J-band flux, the X-ray variability, the visual spectroscopy, the 4.5-micron photometry, the mid-infrared color-magnitude region, the infrared spectral energy distribution and the near-infrared color-color region. The definition of posterior probabilities is given in Section 3.2 of the reference paper and the specific implementation for Carina sources is discussed in detail in Section 4 of the reference paper.

H2_Post_Prob
The 'posterior class probability' that the specific source is a young star in the Carina complex (the H2 hypothesis), based on a naive Bayes classifier using 8 observed or physical source properties: the median X-ray energy, the J-band flux, the X-ray variability, the visual spectroscopy, the 4.5-micron photometry, the mid-infrared color-magnitude region, the infrared spectral energy distribution and the near-infrared color-color region. The definition of posterior probabilities is given in Section 3.2 of the reference paper and the specific implementation for Carina sources is discussed in detail in Section 4 of the reference paper.

H3_Post_Prob
The 'posterior class probability' that the specific source is a background Galactic field star (the H3 hypothesis), based on a naive Bayes classifier using 8 observed or physical source properties: the median X-ray energy, the J-band flux, the X-ray variability, the visual spectroscopy, the 4.5-micron photometry, the mid-infrared color-magnitude region, the infrared spectral energy distribution and the near-infrared color-color region. The definition of posterior probabilities is given in Section 3.2 of the reference paper and the specific implementation for Carina sources is discussed in detail in Section 4 of the reference paper.

H4_Post_Prob
The 'posterior class probability' that the specific source is an extragalactic source (the H4 hypothesis), based on a naive Bayes classifier using 8 observed or physical source properties: the median X-ray energy, the J-band flux, the X-ray variability, the visual spectroscopy, the 4.5-micron photometry, the mid-infrared color-magnitude region, the infrared spectral energy distribution and the near-infrared color-color region. The definition of posterior probabilities is given in Section 3.2 of the reference paper and the specific implementation for Carina sources is discussed in detail in Section 4 of the reference paper.

Assigned_Class
The assigned classification of the X-ray source based on the values of the 4 posterior class probabilities. The authors chose to adopt a class decision rule that assigned a specific class (1, 2, 3 or 4, corresponding to the H1, H2, H3 and H4 hypotheses, respectively, if the largest posterior probability was more than twice the next-largest posterior probability. When no classification posterior probability stood out above the others using this criterion, a source was labeled 'unclassified' and given an assigned_class value of '0'. Thus, to summarize:

  Assigned Class 0 means unclassified
                 1 means foreground Galactic field star
                 2 means young star in Carina complex
                 3 means background Galactic field star
                 4 means extragalactic source
  
The numbers of X-ray sources in these 5 categories are given in Table 4 of the reference paper.

Median_Energy
The median energy of the detected events in the 'total' energy band (0.5 - 8 keV), in keV.

Log_Photon_Flux
The logarithm of the apparent total-band X-ray photon flux F_photon of the source, in units of photons cm-2 s-1. This quantity is the lowest-level calibrated photometric quantity that can be used to compare sources, and is defined (Broos et al. 2010, ApJ, 714, 1582, Section 7.4) using three quantities from Table 1 in Broos et al. (2011, ApJS, 194, 2), as:

        F_photon =Net_Counts/ Mean_Effective_Area/Exposure_Time_Nominal
  
Broos et al. (2011, ApJS, 194, 2) use this quantity to study the spatial variation in detection completeness within the survey.

Log_NH_Pre_Ms
The logarithm of the H I column density, in H atoms cm-2, towards the source, if it is classified as a pre-main sequence star in the Carina Complex, i.e., in the H2 sample, assigned_class = 2, less the massive stars studied by Gagne et al. (2011, ApJS, 194, 5). Estimation of intrinsic (absorption-corrected) flux requires two astrophysical inferences or assumptions: the absorbing column and the spectral shape of the emitting plasma. Getman et al. (2010, ApJ, 708, 1760) describe a set of plasma assumptions that are appropriate for pre-main-sequence stars, a procedure for selecting the best plasma assumption based on apparent X-ray flux in the hard band (2 -8 keV), a technique for inferring the absorbing column with uncertainties from the median X-ray energy statistic once a plasma has been assumed, and a set of calibrations for estimating intrinsic flux with uncertainties. Estimates are not available for very weak sources (those with less than two net counts in the hard band or less than three net counts in the total band).

Log_Lx_Pre_Ms
The logarithm of the intrinsic (absorption-corrected) total-band X-ray luminosity, in erg s-1, of the source, if it is classified as a pre-main sequence star in the Carina Complex, i.e., in the H2 sample, assigned_class = 2, less the massive stars studied by Gagne et al. (2011, ApJS, 194, 5). Estimation of intrinsic (absorption-corrected) flux requires two astrophysical inferences or assumptions: the absorbing column and the spectral shape of the emitting plasma. Getman et al. (2010, ApJ, 708, 1760) describe a set of plasma assumptions that are appropriate for pre-main-sequence stars, a procedure for selecting the best plasma assumption based on apparent X-ray flux in the hard band (2 -8 keV), a technique for inferring the absorbing column with uncertainties from the median X-ray energy statistic once a plasma has been assumed, and a set of calibrations for estimating intrinsic flux with uncertainties. Estimates are not available for very weak sources (those with less than two net counts in the hard band or less than three net counts in the total band). A distance of 2.3 kpc was assumed in the calculation of the luminosity.

Log_NH_Other
The logarithm of the H I column density, in H atoms cm-2, towards the source, if it is unclassified, i.e., assigned_class = 0. The authors also applied the Getman et al. (2010, ApJ, 708, 1760) procedure to sources which were reported to be 'unclassified' or likely contaminants, in anticipation that future studies might conclude that specific members of this group are instead pre-main-sequence stars. To emphasize that this procedure is inappropriate for the current classification, they report the resulting absorption and intrinsic X-ray luminosity estimates for unclassified sources in separate parameters from their counterpart parameters for the classified pre-main sequence stars.

Log_Lx_Other
The logarithm of the intrinsic (absorption-corrected) total-band X-ray luminosity, in erg s-1, of the source, if it is unclassified, i.e., assigned_class = 0. The authors also applied the Getman et al. (2010, ApJ, 708, 1760) procedure to sources which were reported to be 'unclassified' or likely contaminants, in anticipation that future studies might conclude that specific members of this group are instead pre-main-sequence stars. To emphasize that this procedure is inappropriate for the current classification, they report the resulting absorption and intrinsic X-ray luminosity estimates for unclassified sources in separate parameters from their counterpart parameters for the classified pre-main sequence stars.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 9-Jun-2011