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Description
The authors studied the X-ray properties of the young (~1-8M yr) open cluster around the hot (O8 III) star Lambda Ori and compared them with those of the similarly-aged Sigma Ori cluster in order to investigate the possible effects of the different ambient environments. They analyzed an XMM-Newton observation of the cluster using EPIC imaging and low-resolution spectral data. They studied the variability of the detected sources, and performed a spectral analysis of the brightest sources in the field using multi-temperature models. The authors detected 167 X-ray sources above a 5-sigma detection threshold the properties of which are listed in this table, of which 58 are identified with known cluster members and candidates, from massive stars down to low-mass stars with spectral types of ~ M5.5. Another 23 sources were identified with new possible photometric candidates. Late-type stars have a median log L<sub>X</sub>/L<sub>bol</sub> ~ -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 Lambda Ori is dominated by plasma at 0.2 - 0.3 keV, with a weaker component at 0.7 keV, consistent with a wind origin. The coronae of late-type stars can be described by two plasma components with temperatures T<sub>1</sub> ~ 0.3-0.8 keV and T<sub>2</sub> ~ 0.8-3 keV, and subsolar abundances Z ~ 0.1-0.3 Z<sub>sun</sub>, 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 definitive conclusions to be drawn. The authors concluded that 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. The lambda Ori cluster was observed by XMM-Newton from 20:46 UT on September 28, 2006 to 12:23 UT on September 29, 2006 (Obs. ID 0402050101), for a total duration of 56ks, using both the EPIC MOS and PN cameras and the RGS instruments. The EPIC cameras were operated in full frame mode with the thick filter. This table was created by the HEASARC in November 2011 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/530/A150">CDS Catalog J/A+A/530/A150</a> files tablea1.dat ('X-ray sources detected in the Lambda Ori Cluster'), table1,dat ('X-ray and optical properties of sources identified with known cluster members and candidates') and table2.dat ('X-ray sources identified with possible new cluster candidates'). It does not include the objects listed in tablea2.dat ('3-sigma upper limits and optical properties of undetected cluster members and candidates'). This is a service provided by NASA HEASARC .
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