The corona and upper transition region of ε Eridani

Abstract

We present analyses of observations of ε Eridani (K2 V) made with the Low Energy Transmission Grating Spectrometer onboard Chandra and the Extreme Ultraviolet Explorer, supplemented by observations made with the Space Telescope Imaging Spectrograph, the Far Ultraviolet Spectroscopic Explorer and the Reflection Grating Spectrometer onboard XMM-Newton. The observed emission lines are used to find relative element abundances, to place limits on the electron densities and pressures and to determine the mean apparent emission measure distribution. As in a previous paper by Sim & Jordan, the mean emitting area as a function of the electron temperature is derived by comparisons with a theoretical emission measure distribution found from energy balance arguments. The final model has a coronal temperature of 3.4 × 106 K, an electron pressure of 1.3 × 1016 cm-3 K at T e = 2 × 105 K and an area filling factor of 0.14 at 3.2 × 105 K. We discuss a number of issues concerning the atomic data currently available. Our analyses are based mainly on the latest version of CHIANTI (v5.2). We conclude that the Ne/O relative abundance is 0.30, larger than that recommended from solar studies, and that there is no convincing evidence for enhanced coronal abundances of elements with low first ionization potentials. © 2008 The Authors. Journal compilation © 2008 RAS.