A comparison between the X-ray variable Sun and solar-like main sequence stars

Abstract

We analyze the time variations of the solar X-ray luminosity observed with Yohkoh/SXT with the aim to compare the X-ray variability of the Sun with that of the other solar-like main sequence stars as function of the relevant time scales. Since the observational set-up and strategies used to observe the Sun differ from those used for the other stars, we have explored the solar X-ray variability properties starting from the available solar data, trying to reproduce the observational procedures adopted for the stars. We have quantified how the solar variability amplitude increases with the explored time scales and found that solar-cycle variability can contribute at most up to 60% to the spread observed in nearby solar-like star X-ray luminosity distribution functions. The comparison between the Sun and the nearby stars is consistent with a scenario in which a fraction of moderately active stars ( erg/s) have X-ray variability similar to the Sun, while more active stars lack solar-like cyclic coronal activity.