Star Formation in the Outer Galaxy: Coronal Properties of NGC 1893

TL;DR

This study analyzes the X-ray properties of the young star cluster NGC 1893 in the outer Galaxy, finding that its coronal activity is similar to nearby regions, supporting the universality of X-ray emission in young stars.

Contribution

It provides the first detailed X-ray analysis of NGC 1893 in the outer Galaxy, showing its properties are comparable to those of local star-forming regions, indicating environmental effects are minimal.

Findings

X-ray luminosities range from 10^29.5 to 10^31.5 erg/s.

34% of sources show variability, with an average of 0.16 flares per source.

X-ray properties are similar to those of the Orion Nebula Cluster.

Abstract

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.