X-ray observations of the young open cluster Blanco 1. The XMM-Newton view

Abstract

We present the analysis of a 50 ks XMM-Newton observation of the young, metal-rich open cluster Blanco 1. In the sum of EPIC MOS 1, MOS 2 and pn data we have detected 190 X-ray sources, 36 of them having as cluster member as optical counterparts. We have analyzed the X-ray spectra and time variability of the light curves of the cluster sources. Coronal spectra of solar mass stars are characterized by two thermal components at 0.3 and 1.0 keV, with comparable emission measure. One late-A type member shows a coronal spectrum remarkably different from that of solar-type members, thus suggesting an intrinsic difference in the corona production mechanism. The X-ray luminosity distribution of M-type stars suggests a difference with respect to that of coeval, less metal rich Pleiades M-type stars. Short time scale variability is commonly detected in Blanco 1 star coronae, with M-type stars being more variable than G-type stars. Flare-like events axe common but smooth modulations in solar mass stars are also detected. Detailed analysis of two subsequent flares observed in a solar-like cluster star allows us to infer the geometric size and morphology of the coronal structure underlying the flares. An arcade composed of tens of small loops is a likely description of the flaring structure, with possibly the same structure responsible for both flares. On the 6-yr time scale of a comparison with previous ROSAT-HRI observations there is no evidence of an analog of the 11-yr solar cycle. Thus any variability resulting from stellar cycles, if present in young and active stars, must have a lower amplitude (or different cycle periods) than observed for the Sun.