Coronal Evolution of the Sun in Time: High‐Resolution X‐Ray Spectroscopy of Solar Analogs with Different Ages

(abridged) We investigate the long-term evolution of X-ray coronae of solaranalogs based on high-resolution X-ray spectroscopy and photometry withXMM-Newton. Six nearby main-sequence G stars with ages between ~0.1 Gyr and\~1.6 Gyr and rotation periods between ~1d and 12.4d have been observed. Wederive coronal element abundances and the coronal emission measure distribution(EMD). The abundances change from an inverse-First Ionization Potential (FIP)distribution in stars with ages around 0.1 Gyr to a solar-type FIP distributionin stars at ages of 0.3 Gyr and beyond. The coronal EMDs show shapescharacterized by power-laws on each side of the EMD peak. The latter shiftsfrom temperatures of about 10 MK in the most rapidly rotating, young stars totemperatures around 4 MK in the oldest target considered here. The power-lawindex on the cooler side of the EMD exceeds expected slopes for static loops,with typical values being 1.5-3. We interpret this slope with a model in whichthe coronal emission is due to a superposition of stochastically occurringflares, with an occurrence rate that is distributed in radiated energy E as apower-law, dN/dE ~ E^-a. Our EMDs indicate a ~ 2.2-2.8, in excellent agreementwith values previously derived from light curves of magnetically active stars.We derive the range of flare energies required to explain the light-curvemodulation. In an overall scenario, we propose that flaring activity plays alarger role in more active stars. In this model, the higher flare rate isresponsible both for the higher average coronal temperature and the highcoronal X-ray luminosity, two parameters that are indeed found to becorrelated.Comment: 35 pages, 14 figures, 10 table