X-ray spectral and timing characteristics of the stars in the young open cluster IC 2391

Abstract

We present X-ray spectral and timing analysis of the young open cluster IC 2391 observed with XMM-Newton EPIC. By analysing the summed data from MOS1, MOS2 and pn detectors, we detected 99 X-ray sources; 24 of them are members, or probable members, of the cluster, spanning all spectral types. The X-ray spectral analysis of the X-ray brightest cluster stars shows that a spectral model with two thermal components (at kT1 approximate to 0.3 = 0.5 keV and kT2 approximate to 1.0-1.2 keV, respectively) describes well the coronal spectra of G, K and M stars, while a softer 1-T model is appropriate for F stars. The spectra of the A1 type star VXR56 and B8.5 type-star VXR46 axe consistent with the hypothesis that a later type-star companion is responsible of the X-ray observed emission. Variability on short time scales is common among IC 2391 members; the Kolmogorov-Smirnov test applied to the Xray photon time series shows that approximately 46% of the IC 2391 members axe variable at a confidence level > 99%. A very fast rotating star of the cluster unambiguously shows X-ray rotational modulation, while indication of rotational modulation is found in another fast rotating star and in other two stars with unknown rotational period. The comparison of our data with those obtained with ROSAT/PSPC, nine years earlier, and ROSAT/HRI, seven years earlier, shows that there is no evidence of significant variability on these time scales.