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J.J. Drake (1), J.M. Laming (2,3), and K.G. Widing (3)
1) Center for EUV Astrophysics, 2150 Kittredge Street,
University of California, Berkeley, CA 94720
2) SFA
3) Naval Research Laboratory, Washington, D.C. 20375
We present a detailed study of element abundances in the corona of Procyon based on spectroscopic observations obtained with the Extreme Ultraviolet Explorer Satellite (EUVE). Emission measures (EMs) have been derived from observed line fluxes for the elements O, Ne, Mg, Si, S, Ar, Fe and Ni, using the most recent atomic data. The slope of the resulting EM distribution is very similar to the well-known result of 1.5 (EM ~ T^(3/2)) found for the solar corona for log T=5.3-6.0. The abundances in the corona of Procyon are found to be consistent with their photospheric values. No enhancement of species with low first ionization potentials (FIP) is observed, such as is the case for the solar corona: the "FIP effect" appears to be absent in Procyon. We speculate that the dominant emission from the corona and transition region in Procyon could originate in low altitude structures analogous to the solar supergranulation network, which does not appear to exhibit a FIP effect. A considerable body of observational evidence suggests that Procyon is both a "basal" star in terms of its chromospheric activity, and is on the spectral type boundary which separates stars which exhibit activity levels correlated with rotation and those which do not. Such stars are thought by some workers to sustain coronae which are heated predominantly by acoustic means. We also note that an acoustically heated outer atmosphere might not possess sufficientlysmall structures to support a fractionation of elements with respect to FIP. Our results demonstrate that the FIP effect is not an ubiquitous feature of late-type stellar coronae. Consequently, speculations in the literature that the FIP effect observed in cosmic rays is a result of their originating from seed particles injected by late-type stellar coronae must await observational confirmation that the FIP effect does indeed operate on M dwarfs, which are likely to be the dominant particle injection source.
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