Outer atmospheres of cool stars. V. IUE observations of Capella: The rotation-activity connection

Journal Article · Wed Oct 01 04:00:00 EDT 1980 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/158341· OSTI ID:6919140

Ayres, T R; Linsky, J L

We present and analyze ultraviolet spectra of Capella (G6 III +F9 III) obtained with the International Ultraviolet Explorer. High-diepersion spectra in the 115-200 A region taken at orbital velocity crossing show no evidence for the increasing blueshifts with increasing temperature of formation previously inferred from Copernicus observations. We conclude that there is no discernible stellar wind from either component of the system. High-resolution emission-line profiles taken near the elongation at phase 78 days suggest that virtually all the emission in transition-region (TR) lines (2 x 10/sup 4/ K< or =T< or =2 x 10/sup 5/ K) and most of the emission in chromospheric lines (T< or approx. =10/sup 4/ K) come from the late-F secondary of the system. This result is contrary to the assumption made in most previous studies that the slightly more massive Capella primary is the dominant ultraviolet emitter. We propose that the origin of the extraordinarily different activity levels on these otherwise very similar stars can be traced to the one property that is obviously different, namely, rotation: the Capella promary is a normal, sharp-lines, slow rotating giant, whereas the secondary has broader lines and is a rapid rotator for a late-type giant (V sin i< or approx. =30 km s/sup -1/). Such a chromospheric rotation-activity connection has been demonstrated previously in the Ca II emission cores, and is very likely a consequence of enhanced surface magnetic fields produced by increase dynamo action in rapidly rotating, convective stars. We extend the rotation-activity connection to stellar transition regions and suggest, on the basis of published soft X-ray observations of a limited sample of stars, that it is valid for coronae as well.

• Research Organization: Joint Institute for Laboratory Astrophysics, University of Colorado and National Bureau of Standards
• OSTI ID: 6919140
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 241:1; 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
BINARY STARS
CALCIUM IONS
CHARGED PARTICLES
DATA
EMISSION SPECTRA
EXPERIMENTAL DATA
INFORMATION
IONS
MATHEMATICAL MODELS
NUMERICAL DATA
RADIATION FLUX
SPECTRA
STAR MODELS
STARS
STELLAR ATMOSPHERES
STELLAR WINDS
ULTRAVIOLET SPECTRA