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NGC1893CXO - NGC 1893 Chandra X-Ray Point Source Catalog



The outer Galaxy, where the environmental conditions are different from the solar neighbourhood, is a laboratory in which it is possible to investigate the dependence of the star formation process on the environmental parameters. The authors investigate the X-ray properties of NGC 1893, a young cluster (~ 1 - 2 Myr) in the outer part of the Galaxy (galactic radius >= 11 kpc), where they expect differences in the disk evolution and in the mass distribution of the stars, so as to explore the X-ray emission of its members and compare it with that of young stars in star forming regions near to the Sun.

The authors analyze 5 deep Chandra ACIS-I observations with a total exposure time of 450 ks. Source events of the 1021 X-ray sources have been extracted with the IDL-based routine ACIS-Extract. Using spectral fitting and quantile analysis of X-ray spectra, they derive X-ray luminosities and compare the respective properties of Class II and Class III members. They also evaluate the variability of sources using the Kolmogorov-Smirnov test and identify flares in the lightcurves.

The X-ray luminosity of NGC 1893 X-ray members is in the range 1029.5 - 1031.5 erg s-1. Diskless stars are brighter in X-rays than disk-bearing stars, given the same bolometric luminosity. The authors find that 34% of the 1021 lightcurves appear variable and that they show 0.16 flares per source, on the average. Comparing their results with those relative to the Orion Nebula Cluster, they find that, after accounting for observational biases, the X-ray properties of NGC 1893 and the Orion stars are very similar.

The authors conclude that the X-ray properties of stars in NGC 1893 are not affected by the environment and that the stellar population in the outer Galaxy may have the same coronal properties as nearby star-forming regions. The X-ray luminosity properties and the X-ray luminosity function appear to be universal and can therefore be used for estimating distances and for determining stellar properties.

Catalog Bibcode



Star formation in the outer Galaxy: coronal properties of NGC 1893.
    Caramazza M., Micela G., Prisinzano L., Sciortino S., Damiani F.,
    Favata F., Stauffer J.R., Vallenari A., Wolk S.J.
    <Astron. Astrophys. 539, A74 (2012)>
    =2012A&A...539A..74C        (SIMBAD/NED BibCode)


This table was created by the HEASARC in March 2012 based on CDS Catalog J/A+A/539/A74 file catalog.dat, the catalog of 1021 X-ray sources detected towards NGC 1893.


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

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) format.

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. The procedures used to find the positions are discussed in Section 2 of the reference paper.

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. The procedures used to find the positions are discussed in Section 2 of the reference paper.

The Galactic Longitude of the X-ray source.

The Galactic Latitude of the X-ray source.

The statistical positional error of the X-ray source, i.e., the estimated 1-sigma standard deviation of the random component of the position error sqrt(sigmax2 + sigmay2), 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.

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

The estimated net counts extracted in the total energy band (0.5 - 8 keV) in the extraction region of the X-ray source.

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

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

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.

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

The Kolmogorov-Smirnov probability that the X-ray lightcurves of the source is consistent with its being constant.

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.

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

The logarithm of the absorption-corrected total-band (0.5 - 8 keV) luminosity of the X-ray source assuming a distance of 3.6 kpc, in erg/s.

This flag parameter is coded as follows to indicate how the X-ray luminosity was calculated for the specified source (see Section 3.1 of the reference paper for more details):

             a = from fit to a one-temperature model spectrum
             b = from analysis of quantiles
             c = from a conversion factor derived from the analysis of the

Contact Person

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