M. Caramazza, G. Micela, L. Prisinzano, S. Sciortino, F. Damiani, F. Favata, J. R. Stauffer, A. Vallenari, S. J. Wolk
We investigate the X-ray properties of NGC 1893, a young cluster (~ 1-2 Myr)
in the outer part of the Galaxy (galactic radius \geq 11 kpc) where we expect
differences in the disk evolution and in the mass distribution of the stars, 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. We 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, we derive X-ray
luminosities and compare the respective properties of Class II and Class III
members. We also evaluate the variability of sources using the
Kolmogorov-Smirnov test and we identify flares in the lightcurves. The X-ray
luminosity of NGC 1893 X-ray members is in the range 10^29.5 - 10^31.5 erg/s.
Diskless stars are brighter in X-rays than disk-bearing stars, given the same
bolometric luminosity. We found that 34% of the 1021 lightcurves appear
variable and that they show 0.16 flare per source, on average. Comparing our
results with those relative to the Orion Nebula Cluster, we find that,
accounting for observational biases, the X-ray properties of NGC 1893 and the
Orion ones are very similar. The X-ray properties in NGC 1893 are not affected
by the environment and the stellar population in the outer Galaxy may have the
same coronal properties of 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 distance estimations and for determining stellar
properties as already suggested by Feigelson and collaborators.
View original:
http://arxiv.org/abs/1112.0482
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