Magnetic structure in cool stars. XV - The evolution of rotation rates and chromospheric activity of giants

Details Magnetic structure in cool stars. XV - The evolution of rotation rates and chromospheric activity of giants Magnetic structure in cool stars. XV - The evolution of rotation rates and chromospheric activity of giants

Feb 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988a%26a...191..227r&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 191, no. 2, Feb. 1988, p. 227-236. Research supported by Stichting Astronomisc

Astronomy and Astrophysics

Astrophysics

50

Cool Stars, Giant Stars, Late Stars, Stellar Evolution, Stellar Magnetic Fields, Stellar Rotation, Angular Momentum, Calcium, Chromosphere, K Lines

Scientific paper

For cool giants and subgiants the observed dependence of rotational velocity and Ca II H and K line-core emission on color B-V is interpreted in terms of changes in the moment of inertia by stellar evolution. Modeling of the rotational velocity during the evolution of cool giants with masses between 2.0 and 3.0 solar masses, by taking into account the change in the moment of inertia and assuming rigid-body rotation and conservation of angular momentum, describes the observed decrease of v sin i with B-V. The computed evolution of the rotational velocity, together with the empirical relation between the Ca II line-core emission and the rotation rate, explain the observed drop in the Ca II line-core emission for giants at B-V = about 0.95. For subgiants with masses of about 1.5 solar mass, the change in the moment of inertia by itself cannot explain the observed v sin i distribution: there are indications of loss of angular momentum, presumably by magnetic braking.

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