An X-Ray Survey of the Young Stellar Population of the Lynds 1641 and Iota Orionis Regions

Abstract

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 ι 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 ι 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

First stars of theρOphiuchi dark cloud

“…The average N H /A V ratio near ρ Ophiuchi is lower than in Orion or the typical ISM value, and slightly higher than the values of N H /A V found in other low mass star forming regions like NGC 1333, Serpens and L1641 (Winston et al 2007(Winston et al , 2010Pillitteri et al 2013). This evidence could be related to different amounts of ambient UV fluxes.…”

“…The value [4.6] < 12 allows us to distinguish between YSOs at the distance of ρ Ophiuchi (120 pc) and background objects. This is analogous to the cut in IRAC [4.5] magnitude we adopted in Pillitteri et al (2013) to filter out faint background objects in Orion A at d ∼ 415 pc with [4.5] > 14. This selection is valid only around ρ Ophiuchi, where extinction is much lower than, for example, in L1688 core.…”

“…The origin of this value is debated but it could be a limit to the efficiency in the production of X-rays in dynamo driven coronae of active stars (Charbonneau & MacGregor 1992) or a breaking of magnetic loops in fast rotating stars (Jardine & Unruh 1999). Figure 6 shows the distribution of X-ray luminosities of Class III stars earlier than M5 around ρ Ophiuchi and the analog curves of stars in L1688 (from DROXO; Pillitteri et al 2010), and from L1641 (Pillitteri et al 2013). For L1688 we report the total and a corrected distribution after removing some suspicious members from the list of Bontemps et al (2001), mostly upper limits to luminosity.…”

Slingshot mechanism in Orion: Kinematic evidence for ejection of protostars by filaments

“…The cluster is predominantly composed of disk sources (Class II stars), from which we estimate an age of 2 Myr. Moreover, 2.9 pc further north is an older cluster, which Pillitteri et al (2013) showed is predominantly composed of photospheric (Class III) stars, with a minority of Class II stars. Hence, it is yet older, perhaps 4 Myr.…”

“…While the orphan cluster is heavily populated by disk sources (i.e., those found by Megeath et al 2012 to have Spitzer infrared (IR) excesses) there is another cluster (NGC 1981), which lies 3 pc further to the north (hence closer to Orion B), and which was identified by Pillitteri et al (2013) as containing relatively few Megeath et al (2012) disk sources but a much larger number of photospheric (Class III) stars, meaning that it is older.…”