XMM-Newton observations of the young open cluster around lambda Orionis

TL;DR

This study used XMM-Newton to analyze the X-ray properties of the young lambda Orionis cluster, revealing details about stellar activity, plasma temperatures, and the influence of environment on X-ray emission.

Contribution

First detailed X-ray analysis of the lambda Orionis cluster, comparing its properties with similar clusters and examining effects of environment on stellar activity.

Findings

Detected 167 X-ray sources, 58 identified with known members.

Late-type stars exhibit high X-ray activity close to saturation.

X-ray emission from the hot star is wind-dominated.

Abstract

We studied the X-ray properties of the young (~1-8 Myr) open cluster around the O8III star lambda Ori using XMM-Newton. We detected 167 X-ray sources, of which 58 are identified with known cluster members, 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 LX/Lbol ~ -3.3, close to the saturation limit. Variability was observed in 35% of late-type members, including six flaring sources. The emission from the central hot star lambda 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 T1~0.3-0.8 keV and T2~0.8-3 keV, and subsolar abundances Z~0.1-0.3 Zsun, 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. The X-ray properties of lambda Ori late-type stars are comparable to those of the coeval sigma Ori cluster, suggesting that stellar activity in lambda Ori has not been significantly affected by the different ambient environment.