The study: “XMM-Newton imaging of V1818 Orionis: a young stellar group on the eastern edge of the κ Ori ring” of I. Pillitteri (INAF-OAPA) recently published by A&A

The Orion Molecular Cloud is likely the best target for studying star formation. In the past few million years, in fact, this cloud formed thousands stars over a wide range of stellar masses and in several episodes with different characteristics: From isolated low mass stars to populated and massive stellar clusters; from star formation from self-collapsing clouds to triggered star formation; from environments where stars and planets can form unperturbed to environments providing a strong feedback on the formation and evolution of stars and planets. Thanks to this properties and the relative small distance of this cloud to the Sun (this is the closest star forming region to us with such characteristics) the Orion Molecular Cloud is indeed one of the most studied regions in the sky.

 

In the study “XMM-Newton imaging of V1818 Orionis: a young stellar group on the eastern edge of the κ Ori ring” of Ignazio Pillitteri (INAF- Osservatorio Astronomico di Palermo), the properties of the region around the Herbig Be star V 1818 Ori are analyzed using new X-ray observations from XMM/Newton and archival infrared data (WISE and 2MASS). The authors have identified 31 previously unknown pre-main sequence stars lying along a ring surrounding the massive star Kappa Ori (Saiph). Such structures are typically found in clouds hosting massive stars, being modeled by their intense stellar wind and energetic radiation, and may be a smoking gun for triggered star formation. This research has found that this group of stars formed between 3 and 5 million years ago and their distance is between 815 e i 915 light years, being in the foreground of the South region of the Orion Molecular Cloud (called Orion A), which is between 1250 and 1400 light years away. This research demonstrates the effectiveness of X-ray observations not only to select young stars, but also to estimate their distance by comparing their X-ray luminosity with that of known ensemble of stars.

 

The figure (link) shows a composite image of the region around V1818 Ori (in the center), with optical in blu, infrared at 12μm in green and 22μm in red. The small white regions mark the XMM observations analyzed in  Pillitteri et al. (2016) and Pillitteri et al. (2013).