Cepheid masses and Cepheid winds
Abstract
Masses of Cepheids with bumps in their light and velocity curves (bump Cepheids) and those with two pulsation modes (beat or double-mode Cepheids) can be made equal to masses obtained from the evolution theory mass-luminosity relation if they have helium-enriched convection zones. The cause of this enrichment cannot be diffusion of helium from below with subsequent mixing in and between the H plus He I and He II convection zones. The probable cause of the composition inhomogeneity seems to be a Cepheid wind which depletes hydrogen more than helium as apparently occurs in the solar wind. A layer with Y equals 0.75 and Z equals 0.02 external to the 70,000 K level allows 7-solar-mass Cepheids to give the proper periods and light and velocity curve bumps at their evolution theory luminosity. This helium-deficient wind, if only a little stronger than that in the Sun, needs 1,000,000-10,000,000 years. Barely enough time is available for 7-solar-mass Cepheids, but there is plenty for the 4-5-solar-mass beat Cepheids to give their observed period ratios.
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