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High-dispersion observations of alpha Bootis (K1 III) with the International Ultraviolet Explorer
Ayres, T. R.; Judge, P.; Jordan, C.; Brown, A.; Linsky, J. L.
AA(Colorado, University, Boulder), AB(Oxford University, England), AC(Oxford University, England), AD(Joint Institute for Laboratory Astrophysics, Boulder, CO), AE(Joint Institute for Laboratory Astrophysics, Boulder, CO)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 311, Dec. 15, 1986, p. 947-959. SERC-supported research. (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
K Stars, Main Sequence Stars, Red Giant Stars, Spaceborne Astronomy, Stellar Evolution, Stellar Spectra, Ultraviolet Spectra, Abundance, Emission Spectra, Iue, Spectral Energy Distribution, Stellar Luminosity
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The authors have obtained very deeply exposed IUE echelle spectrograms of the bright, early-K giant Arcturus. They did not detect significant flux in the most prominent high-excitation species of a solar-like transition zone, C IV lambda1548.2. The presence of a weak feature of Si III] lambda1892.0, and possibly also Si IV lambda1393.8, indicates the existence of a small amount of plasma at temperatures as hot as 6×104K. Measurements of C II] multiplet UV0.01 near 2325 Å provide a lower limit of about 5×109cm-3 for the electron density in the chromospheric layers. C II UV1 (1335 Å) emission is very weak. These results confirm that the "coronal" activity of the old red giants is considerably diminished from that of even the "quietest" of their main-sequence predecessors, stars like the Sun.

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