Evolution of chromospheres and coronae in solar mass stars : a far-ultraviolet and soft X-ray comparison of Arcturus (K2III) and alf CEN A (G2V).
Abstract
IUE far-UV and Einstein Observatory soft X-ray observations for the red giant Arcturus and the nearby yellow dwarf Alpha-Centauri A, which are archetypes of solar mass stars in different stages of evolution, are compared. Evidence is found for neither coronal soft X-ray emission from the red giant, at surface flux levels of only 0.0006 that detected previously for the yellow dwarf, nor C II and IV resonance line emission at surface flux levels of only 0.02 those of the yellow dwarf. The resonance line upper limits and previous detections of the C II intersystem UV multiplet 0.01 near 2325 A provide evidence for an Arcturus outer atmosphere that is geometrically extended, tenuous and cool. The red giant has, in addition, a prominent cool stellar wind. An extensive tabulation of line identifications, widths and fluxes for the IUE far-UV echelle spectra of the two stars is given, and two competing explanations for the Wilson-Bappu effect are discussed.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 1982
- DOI:
- Bibcode:
- 1982ApJ...263..791A
- Keywords:
-
- Chromosphere;
- Far Ultraviolet Radiation;
- Red Giant Stars;
- Stellar Coronas;
- Stellar Evolution;
- X Ray Sources;
- Iue;
- Line Spectra;
- Radiant Flux Density;
- Resonance Lines;
- Spectral Line Width;
- Stellar Mass;
- Stellar Winds;
- Ultraviolet Spectra;
- X Ray Spectra;
- Astrophysics