Hostname: page-component-745bb68f8f-b6zl4 Total loading time: 0 Render date: 2025-01-13T00:26:53.472Z Has data issue: false hasContentIssue false
  • English
  • Français

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

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

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

References

Antiochos, S.K. 1994, The physics of coronal closed-field structures, Adv. Space Res., 14(4), 139 Google Scholar
Ayres, T.R. 1988, A spectral dissection of the ultraviolet emissions of Capella, ApJ, 331, 467 Google Scholar
Ayhes, T.R., et al. 1995, The RIASS Coronathon: Joint X-ray and ultraviolet observations of normal F-K stars, ApJS, 96, 223 Google Scholar
Bowyer, S. & Malina, R.F. 1991, The EUVE Mission, in Extreme Ultraviolet Astronomy, ed. Malina, R.F. & Bowyer, S., New York: Pergamon, 397 Google Scholar
Cox, A.N., Livingston, W.C. & Matthews, M.S. (EDITORS) 1991, Solar Interior and Atmosphere, Univ. of Arizona Press Google Scholar
Dupree, A.K., Brickhouse, N.S., Doschek, G.A., Green, J.C., & Raymond, J.C. 1993, The extreme ultraviolet spectrum of Alpha Aurigae Capella, ApJL, 418, L41 Google Scholar
Gray, D.F. 1989, The rotational break for G giants, ApJ, 347, 1021 Google Scholar
Mewe, R., Gronenschild, E.H.B.M. & Van Den Oord, G.H.J. 1985, Calculated X-radiation from optically-thin plasmas. V., A&AS, 62, 197 Google Scholar
Parker, E.N. 1988, Nanoflares and the solar X-ray corona, ApJ, 330, 474 Google Scholar
Schrijver, C.J. & Pols, O.R. 1993, Rotation, magnetic braking, and dynamos in cool giants and subgiants, A&A, 278, 51 Google Scholar
Simon, T. & Drake, S.A. 1989, The evolution of chromospheric activity of cool giants and subgiant stars, ApJ, 346, 303 Google Scholar