Energy release in stellar coronae Original Research Article

Stellar coronae pose a number of fundamental problems with regard to their high temperatures, their production of high-energy particles, and their stability against several energy loss mechanisms. The solution to most of these problems is Likely to be found in the ubiquitous coronal magnetic fields that release the required energy continuously or episodically. Stellar coronal energy losses are predominantly diagnosed by X-ray, extreme-ultraviolet, and radio emissions but they all are secondary products of the actual primary energy release. The present paper discusses evidence and diagnostics for the primary energy release and energy transport, focusing on i) the hypothesis that active stellar coronae are heated by a stochastic sequence of flares, and ii) that these flares involve chromospheric evaporation to increase the coronal temperature, its emission measure, and the electron density. Optical and nonthermal radio emissions point at an important role of accelerated electrons in the primary energy release.