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Spectra of three Cepheids (RX Aur, X Cyg and T Mon) and 11 non -variable
supergiants are analyzed. Additional evidence is presented for the presence
of non -variables within the Cepheid strip. Temperatures determined from
Ha line profiles and broad band photometry were used together with model
atmospheres and line strengths from the spectra to determine the gravities,
turbulent velocities and element abundances. The gravities of the Cepheids
appear to be lower than for the non -variables at the same luminosity while
the turbulent velocities are higher. No differences of significance are
found in the element abundances. The gravity differences can be explained
either in terms of mass loss in the Cepheids or very low helium abundance in
the non -variables. The former interpretation fails to explain why some Cepheid
strip stars do not vary while the latter raises problems in connection with
the origin of the elements. If we assume that pulsation causes some mass
loss a more consistent picture emerges in which only moderate helium deficiencies
are required in the non-variables.
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