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J.J. Drake (1), J.M. Laming (2,3), K.G. Widing (3), J.H.M.M. Schmitt (4), B. Haisch (1), and S. Bowyer (1)
1) Center for EUV Astrophysics, 2150 Kittredge Street,
University of California, Berkeley, CA 94720
2) SFA
3) Naval
Research Laboratory, Washington, D.C. 20375
4) MPE , Giessenbachstr.
1, Garching, 8046, Germany
The chemical composition of the Sun has been studied extensively over many years. In recent years it has been discovered that the chemical composition of the solar corona is not the same as that of the underlying photosphere. Elements with a first ionization potential (FIP) <= 10 eV (e.g., Fe, Mg, Si, Ca) are observed to be enhanced relative to those with FIP >= 10 eV (e.g., O, Ne, S) in the corona by factors of 3-10 with respect to the photosphere. This phenomenon is now known as the "FIP Effect." The mechanism responsible for it is currently unknown. Is the Sun unique, or do other stellar coronae share a solar-like enhancement of low FIP species? Prior to the recent launch of the Extreme Ultraviolet Explorer Satellite (EUVE) the spectroscopic capability required to answer this question did not exist. Based on spectroscopic observations of the corona of the nearby F5 IV star Procyon obtained with EUVE, we have now made the first estimates of the relative abundances of high and low FIP species in the corona of a star other than the Sun. The results indicate that, in contrast to the Sun, the FIP effect is not present in the corona of Procyon. The FIP effect is, therefore, not an ubiquitous feature of late-type stellar coronae. Whether the prevailing stellar situation is that of the Sun or that of Procyon is of fundamental interest to the physics of stellar outer atmospheres and also has a bearing on the origin of cosmic rays.
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