X-ray emission and structure of coronae of active late-type dwarfs

A method for determination of density in stellar coronae from X-ray data is suggested. Its application to 45 G, K, M main sequence stars shows that the density at the corona base increase by the transition from G stars to M0-M3 stars, and drops thereafter. The rising-density branch is connected with the intensification of solar-type activity processes on G - K stars. The properties of the X-ray emission of active M3 - M6 stars, its rapid variability and its association with flare activity and with nonthermal radio emission apparently evidence that heating of the coronae of these stars is due to numerous processes of the subflare type