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from III - Convection, Rotation and Activity
Published online by Cambridge University Press: 04 August 2010
The issue of the variability of coronal emission is a current problem of stellar physics. Properties of X-ray variability, amplitude and time scales give us information on the physics underlying the coronal emission. In this work we present results from a systematic analysis of X-ray variability of nearby M stars, mainly focused on medium and long term time scales. Taking advantage of archival data of ROSAT-PSPC observations, we explore time scales from days to months. Variability is present at all explored time scales and its amplitude is independent of stellar X-ray and visual luminosity. Results are compared with solar X-ray variability properties suggesting that in dM stars emitting Structures have a spatial distribution more homogenous that in the Sun. Analogous studies on dM stars of the Pleiades indicate that in this cluster the spread observed in the X-ray luminosity function can be explained in terms of variability.
Introduction
The study of temporal variations is a very powerful tool to characterize and study the properties of a population of X-ray sources. Studies of typical time scales and amplitude of the observed variability can provide useful information on dimensions and physical conditions of the regions where X-ray emission originates. Comparative studies of the variability properties within a homogeneous class of X-ray sources are useful to determine or constrain the mechanisms generating their X-ray emission. To pursue such studies, a large number of homogenous observations are required.
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