EUVE Observations of Algol: Detection of a Continuum and Implications for the Coronal [Fe/H] Abundance

Robert A. Stern (1,5), James R. Lemen (1), Jürgen H.M.M. Schmitt (2,3), and John P. Pye (4)

1) Solar and Astrophysics Laboratory, Lockheed Palo Alto Research Laboratory,O/91-30, Bldg. 252, 3251 Hanover St., Palo Alto CA 94304
2) Center for EUV Astrophysics, 2150 Kittredge Street, University of California, Berkeley, CA 94720
3) Max-Planck-Institut für Extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany
4) Physics and Astronomy Department, University of Leicester, University Road, Leicester LE1 7RH, UK
5) EUVE Guest Investigator and Visiting Investigator, Center for EUV Astrophysics

Accepted for publication in the Astrophysical Journal Letters

Abstract

We report results from the first extreme ultraviolet spectrum of the prototypical eclipsing binary Algol (beta Per), obtained with the spectrometers on the Extreme Ultraviolet Explorer (EUVE). The Algol spectrum in the 80--350 Å range is dominated by emission lines of Fe XVI--XXIV, and the He II 304Å\ line. The Fe emission is characteristic of high temperature plasma at temperatures up to at least log T ~7.3 K. We have successfully modeled the observed quiescent spectrum using a continuous emission measure distribution with the bulk of the emitting material at log T > 6.5. We are able to adequately fit both the coronal lines and continuum data with a cosmic abundance plasma, but only if Algol's quiescent corona is dominated by material at log T > 7.5, which is physically ruled out by prior X-ray observations of the quiescent Algol spectrum. Since the coronal [Fe/H] abundance is the principal determinant of the line-to-continuum ratio in the EUV, allowing the abundance to be a free parameter results in models with a range of best fit abundances ~15--40 % of solar photospheric [Fe/H]. Since Algol's photospheric [Fe/H] appears to be near-solar, the anomalous EUV line-to-continuum ratio could either be the result of element segregation in the coronal formation process, or other, less likely mechanisms that may enhance the continuum with respect to the lines.

Keywords: ultraviolet: stars, stars: abundances, stars: coronae, binaries: eclipsing

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