The relation of chromospheric activity to convection, rotation, and evolution off the main sequence

Details The relation of chromospheric activity to convection, rotation, and evolution off the main sequence The relation of chromospheric activity to convection, rotation, and evolution off the main sequence

Dec 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apj...299..286g&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 299, Dec. 1, 1985, p. 286-294.

Astronomy and Astrophysics

Astrophysics

99

Chromosphere, Late Stars, Main Sequence Stars, Stellar Activity, Stellar Evolution, Stellar Rotation, Calcium, Convective Flow, F Stars, Subgiant Stars

Scientific paper

The mean level of chromospheric emission associated with magnetic activity in late-type main-sequence stars has been shown to correlate well with a star's rotation period normalized to the convective turnover time scale. This paper presents an internally self-consistent grid of stellar structure parameters (convective turnover time scales, moments of inertia, etc.) for both the zero-age main sequence and for stars evolved well off the main sequence. The value of alpha (mixing-length parameter) which best fits the observed Ca II H and K emission fluxes and rotation periods is found to depend sensitively on details of the adopted B-V value versus effective temperature and on details of the theory. One star in the Wilson survey, HD 124850, is an active subgiant with a surprisingly short rotation period. The most likely model for HD 124850 is that of an early F star, originally, which resided on the main sequence in an inactive mode. It then evolved into a subgiant while retaining its primeval angular momentum, and the lengthening convective turnover time scale of its deepened envelope has induced fresh dynamo-related activity.

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