XMM-Newtonobservations of the young open cluster aroundλ Orionis

Abstract

Aims. We studied the X-ray properties of the young (∼1−8 Myr) open cluster around the hot (O8 III) star λ Ori and compared them with those of the similarly-aged σ Ori cluster to investigate possible effects of the different ambient environment. Methods. We analysed an XMM-Newton observation of the cluster using EPIC imaging and low-resolution spectral data. We studied the variability of detected sources, and performed a spectral analysis of the brightest sources in the field using multi-temperature models.Results. We detected 167 X-ray sources, of which 58 are identified with known cluster members and candidates, from massive stars down to low-mass stars with spectral types ∼M5.5. Another 23 sources were identified with new possible photometric candidates. Late-type stars have a median log L X /L bol ∼ −3.3, close to the saturation limit. Variability was observed in ∼35% of late-type members or candidates, including six flaring sources. The emission from the central hot star λ Ori is dominated by plasma at 0.2−0.3 keV, with a weaker component at 0.7 keV, consistently with a wind origin. The coronae of late-type stars can be described by two plasma components with temperatures T 1 ∼ 0.3−0.8 keV and T 2 ∼ 0.8−3 keV, and subsolar abundances Z ∼ 0.1−0.3 Z , similar to what is found in other star-forming regions and associations. No significant difference was observed between stars with and without circumstellar discs, although the smallness of the sample of stars with discs and accretion does not allow us to draw definitive conclusions. Conclusions. The X-ray properties of λ Ori late-type stars are comparable to those of the coeval σ Ori cluster, suggesting that stellar activity in λ Ori has not been significantly affected by the different ambient environment.

Spectroscopy of very low-mass stars and brown dwarfs in the Lambda Orionis star-forming region

“…9. Spectroscopically confirmed members from Paper I that lie in one of the two XMM-Newton pointings from Barrado et al (2011) or in the central one from Franciosini & Sacco (2011). We show in different colors objects with mass below (in black) and above (in blue) 0.3 M (the completeness limit for Barrado et al 2011).…”

“…Furthermore, we used the measurements and parameters derived for confirmed members published in Dolan & Mathieu (1999); Barrado y Navascués et al (2007); Sacco et al (2008); Maxted et al (2008); Morales-Calderón (2008); Bayo (2009); Barrado et al (2011) and Franciosini & Sacco (2011).…”

“…), and of the X-ray data presented in Barrado et al (2011) and Franciosini & Sacco (2011). The photometric database includes photometry from the optical to the midinfrared (MIR).…”

“…For the EW(Hα) measurements we have gathered data from Sacco et al (2008), Dolan & Mathieu (1999) and this work. We have highlighted the sources detected in X-rays according to Barrado et al (2011) and/or Franciosini & Sacco (2011 with large stars, and have joined with a gray solid line different measurements of EW(Hα) corresponding to the same source. Left: effective temperature vs. Hα equivalent width (positive for emission) along with the saturation criterion.…”

“…2, Barrado et al (2011) presented the analysis of the XMM-Newton observations of two fields in C69. Several months later, Franciosini & Sacco (2011) complemented the study by adding an extra field that covers the vicinity of the massive star λ Ori, roughly at the center of the cluster.…”