CA II emission from late-type stars.

The use of Ca II spectra to investigate dynamical phenomena in stellar chromospheres is discussed in a review of recent observational and theoretical studies. Solar and stellar observations are surveyed, and sample data are shown graphically. Doppler-shift and non-LTE theories of line formation and semiempirical non-LTE models of atmospheric structure are explained, and the limitations of the latter are indicated. The need for more realistic models of atmospheric oscillations, magnetic effects, mass loss, and for more observations of the fine structure of the solar Ca II lines, is stressed.