An X-rays Survey of the Young Stellar Population of the Lynds 1641 and Iota Orionis Regions. (arXiv:1303.3996v1 [astro-ph.SR])

An X-rays Survey of the Young Stellar Population of the Lynds 1641 and Iota Orionis Regions. (arXiv:1303.3996v1 [astro-ph.SR]):
We present an XMM-Newton survey of the part of Orion A cloud south of the
Orion Nebula. This survey includes the Lynds 1641 (L1641) dark cloud, a region
of the Orion A cloud with very few massive stars and hence a relatively low
ambient UV flux, and the region around the O9 III star Iota Orionis. In
addition to proprietary data, we used archival XMM data of the Orion Nebula
Cluster (ONC) to extend our analysis to a major fraction of the Orion A cloud.
We have detected 1060 X-ray sources in L1641 and Iota Ori region. About 94% of
the sources have 2MASS & Spitzer counterparts, 204 and 23 being Class II and
Class I or protostars objects, respectively. In addition, we have identified
489 X-ray sources as counterparts to Class III candidates, given they are
bright in X-rays and appear as normal photospheres at mid-IR wavelengths. The
remaining 205 X-ray sources are likely distant AGNs or other galactic sources
not related to Orion A. We find that Class III candidates appear more
concentrated in two main clusters in L1641. The first cluster of Class III
stars is found toward the northern part of L1641, concentrated around Iota Ori.
The stars in this cluster are more evolved than those in the Orion Nebula. We
estimate a distance of 300-320 pc for this cluster and thus it is closer than
the Orion A cloud. Another cluster rich in Class III stars is located in L1641
South and appears to be a slightly older cluster embedded in the Orion A cloud.
Furthermore, other evolved Class III stars are found north of the ONC toward
NGC 1977.