Implications from extreme-ultraviolet observations for coronal heating of active stars

Extreme Ultraviolet Explorer (EUVE) data of two active solar analogs, 47 Ca s and EK Dra, were used to investigate flare statistics and the distributio n of the flare occurrence rate in energy. The EUVE satellite observed each star for almost 7 days. Simultaneous spectral data from its spectrometers w ere used to derive temperature and abundance characteristics of their coron ae. The emission models were derived from differential emission measure dis tributions by fitting optically thin thermal models to the spectra. The Dee p Survey instrument photon lists were analyzed by applying different time b innings. A total of 28 flares were identified for further analysis. The tim ing study provided estimates for the total radiative energy loss of each fl are. The differential distribution of flares in total X-ray energy is found to be a power law (dN/dE proportional to E-alpha, with alpha approximate t o 2.2 +/- 0.2) valid in the energy range between 3 x 10(33) and 6 x 10(34) ergs. The power-law index is larger than that for typical solar flares but is similar to indices found recently for small-scale solar events. If the p ower law continues to energies of moderate solar flares, then the total ene rgy emitted by the ensemble of all flares may suffice to explain all of the observed flaring and "quiescent" X-ray emissions of the two stars. A consi derable portion, if not all, of the energy required to heat their coronae c ould thus be provided by flares.