STELLAR CORONAL ABUNDANCES. IV. EVIDENCE OF THE FIP EFFECT IN THE CORONA OF ε ERIDANI?

摘要

We present an analysis of the EUV spectrum of the chromospherically active star ε Eridani (K2 V) recorded by the Extreme-Ultraviolet Explorer satellite. We have identified many lines from different elements (O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni) with first ioriization potential (FIP) above and below about 10 eV (high and low FIP, respectively) and have used the measured relative intensities of these to investigate the emission measure (EM) distribution and the coronal element abundances. The spectrum of ε Eri reveals much hotter plasma than the quiet Sun and, as such, is interesting to compare with EUV spectra of solar flares. The EM distribution is found to be sharply peaked near log T = 6.5. The data suggest that a solar-like FIP effect is in operation, although the limited number of high-FIP lines detected, together with the sharply peaked shape of the EM distribution and low signal-to-noise ratio of the spectra, preclude a definitive judgement. However, we can conclude that there cannot be an enhancement of low-FIP species in the corona of ε Eri significantly larger than that seen in the "average" solar corona, which may imply that the magnitude of the FIP effect does not seem to increase with increasing stellar activity, but this should be confirmed by other cases.