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)

Journal Article · Wed Dec 15 04:00:00 EST 1982 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/160549· OSTI ID:6151055

Ayres, T R; Simon, T; Linsky, J L

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), Journal Name: Astrophys. J.; (United States) Vol. 263:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics &amp; Cosmology-- Stars &amp; Quasi-Stellar
Radio &amp; X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
DWARF STARS
ELECTROMAGNETIC RADIATION
FAR ULTRAVIOLET RADIATION
GIANT STARS
IONIZING RADIATIONS
MAGNETIC FIELDS
RADIATION FLUX
RADIATIONS
RED GIANT STARS
SOFT X RADIATION
SPECTRA
STAR EVOLUTION
STARS
STELLAR ATMOSPHERES
STELLAR WINDS
ULTRAVIOLET RADIATION
ULTRAVIOLET SPECTRA
X RADIATION
X-RAY SPECTRA