No CrossRef data available.
Published online by Cambridge University Press: 12 April 2016
In the beginning of this review, I paraphrase three statements from Paul W. Merrill (1960). (1) In the spectra of long-period variables, absorption lines of neutral metals show a shortward displacement increasing algebraically with excitation potential, probably due to atoms moving outward in the star’s upper atmosphere with an expansion velocity of the order of 20 km s-1. (2) About 6 weeks after maximum light emission components appear within the broad absorption at H and K of Ca II, but displaced about -100 km s-1. A similar, but less extreme, behaviour is known for classical cepheids. (3) In quasi-constant red giants, the resonance lines of Ca II, Ca I, and SR II show circumstellar components displaced shortward relative to the normal stellar photospheric lines by a velocity which is correlated with the spectral type, typically -8 km s-1 for M6 II to -25 km s-1 for class M0 III.