CA II H emission line cores of late-type dwarfs - Variability measurements and velocity field diagnostics

Crivellari, L.; Vladilo, G.; Beckman, J. E.; Foing, B. H.
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Astronomy and Astrophysics (ISSN 0004-6361), vol. 174, no. 1-2, March 1987, p. 127-138.

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High-resolution spectra of Alpha Cen B, Xi Boo A, 70 Oph A, and Epsilon Ind obtained using the Coude Echelle Spectrometer and the 1.4-m Coude Auxiliary Telescope of ESO are analyzed. Variations in the normalized fluxes for the four dwarfs are described. Position and intensity measurements of the Ca II H features are examined. The use of the spectra for chromospheric velocity field diagnostics is discussed. The data reveal that it is possible to separate the effects of plages from those due to vertical velocity fields; in some stars the H core samples net upflow and in other net downflow; the layer sampled by the H3 feature shows a velocity close to that defined by the photospheric rest frame; and the H2V/H2R asymmetry is useful as a linear measure of the chromospheric vertical velocity gradient.