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 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 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 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.
Pillitteri, I., Wolk, S. J., Megeath, S. T., Allen, L., Bally, J., Gagné, M., Gutermuth, R. A., Hartman, L., Micela, G., Myers, P., Oliveira, J. M., Sciortino, S., Walter, F., Rebull, L., & Stauffer, J. (2013). An X-Rays Survey of the Young Stellar Population of the Lynds 1641 and Iota Orionis Regions. arXiv Retrieved from http://digitalcommons.wcupa.edu/geol_facpub/20