A DETERMINATION OF THE CORONAL EMISSION MEASURE DISTRIBUTION IN THE YOUNG SOLAR ANALOG EK DRACONIS FROM ASCA EUVE SPECTRA/

We present the results of a coronal differential emission measure (DEM ) analysis of the nearby analog of the young Sun, EK Draconis, using d ata obtained with the ASCA and EUVE satellites. Various methods (inclu ding a CLEAN algorithm, a polynomial fit, a direct inversion method, a genetic algorithm, and a multitemperature fit) have been applied to r econstruct the DEM between 0.1 and 100 MK. The spectra from the four A SCA detectors and the two spectra from the short-wavelength and the me dium-wavelength detectors of EUVE were subject jointly to the algorith ms, taking into account both emission lines and continua. All methods converge to a DEM distribution that is essentially bimodal: we find tw o significant peaks near 7 MK and near 18 MK with a deep minimum aroun d 10 MK. Little plasma is found at temperatures below 3-4 Mit, despite EUVE's sensitivity to this temperature regime. We argue that the DEM distribution seen in EK Dra is induced by the properties of the radiat ive cooling function of a thermal, optically thin plasma. From an elem ental abundance analysis, an Fe abundance of 0.83 times the correspond ing solar photospheric abundance is found, and an abundance of ME of 1 .69 times the solar photospheric abundance, which may indicate for thi s specific element a first ionization potential effect similar to that found in the solar corona.