Evolution of chromospheres and coronae in solar mass stars: A far-ultraviolet and soft x-ray comparison of Arcturus (K2III) and Alpha Centauri A (G2 V)
We compare IUE far-ultraviolet and Einstein soft X-ray observations of the red giant Arcturus (..cap alpha.. Booetis, K2III) and the nearby yellow dwarf ..cap alpha.. Centauri A (G2 V), which are archetypes of solar mass stars in very different stages of evolution. We find no evidence for coronal (Troughly-equal10/sup 6/ K) soft X-ray emission from the red giant at surface flux levels of only 0.0006 (3sigma) that detected previously for ..cap alpha.. Cen A, and no evidence for C iv lambdalambda1548, 1551 (Troughly-equal10/sup 5/ K) or C ii lambdalambda1335, 1336 (Troughly-equal2 x 10/sup 4/ K) resonance line emission at surface flux levels of only 0.02 (3sigma) those of the yellow dwarf. Instead of a solar-like hot corona and warm (Troughly-equal10/sup 5/ K) transition region, the resonance line upper limits and previous detections of the C ii intersystem UV multiplet 0.01 near 2325 A provide evidence that the outer atmosphere of Arcturus is geometrically extended (..delta..happrox.R/sub asterisk/), tenuous (n/sub e/roughly-equal3 x 10/sup 8/ cm/sup -3/), and cool (T< or approx. =10/sup 4/ K).
- Research Organization:
- Laboratory for Atmospheric and Space Physics, University of Colorado
- OSTI ID:
- 6151055
- Journal Information:
- Astrophys. J.; (United States), Vol. 263:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
DWARF STARS
STAR EVOLUTION
STELLAR ATMOSPHERES
ULTRAVIOLET SPECTRA
X-RAY SPECTRA
RED GIANT STARS
FAR ULTRAVIOLET RADIATION
MAGNETIC FIELDS
RADIATION FLUX
SOFT X RADIATION
STELLAR WINDS
ATMOSPHERES
ELECTROMAGNETIC RADIATION
GIANT STARS
IONIZING RADIATIONS
RADIATIONS
SPECTRA
STARS
ULTRAVIOLET RADIATION
X RADIATION
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources