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Hot Times in the Hertzsprung Gap

Published online by Cambridge University Press:  12 April 2016

Thomas R. Ayres
Thomas R. Ayres*
Affiliation:
Center for Astrophysics and Space Astronomy, Campus Box 389, University of Colorado, Boulder, CO 80309, USA

Abstract

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Moderate-mass giants represent a touchstone for probing the mechanisms of magnetic activity among fast-rotating convective stars. Extreme ultraviolet and soft X-ray observations of such stars detect generally hot coronae: the Hertzsprung-gap giants (F5–G2), in particular, have remarkable high-excitation peaks (107 K, or hotter) in their emission-measure distributions. While the high-temperature coronal plasmas are reminiscent of violent solar flares, the high-energy spectra of the Hertzsprung-gap giants appear to be quite steady over time; in contrast to other hot-corona objects whose optical light curves carry the stamps of starspots, and whose high-excitation emissions are sporadically—and dramatically—variable. The constancy of the Hertzsprung-gap stars is particularly puzzling in light of high-dispersion FUV spectroscopy that reveals supersonic flows in their 105 K subcoronal “transition zones.”

Type
III. Coronae of Cool Stars
Information
International Astronomical Union Colloquium , Volume 152: Astrophysics in the Extreme Ultraviolet , 1996 , pp. 113 - 120
Copyright
Copyright © Kluwer 1996

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