Nouvelle evidence pour la perte de masse dans les cepheides classiques.

Frequency-period data on Cepheids in the Magellanic Clouds and the Galaxy are discussed for evidence of mass loss effects. Noting the connection between mass loss and excessive brightness, the typical rate of mass loss is shown to determine the incidence of massive Cepheids. It is found that Cepheids that have expelled sufficient mass will reside in the spectral domain G-K for larger periods than in other spectral ranges during their evolution. The period-luminosity relationship defined as a function of metallicity is determined to accurately account for Cepheids in the Galaxy and Magellanic Clouds. The objects in the Galaxy have periods which do not exceed 50 days. It is suggested that the mass loss rates of the Cepheids are slightly less than those of Wolf-Rayet stars and close to that of red supergiants. Convective overshooting and turbulent diffusion are considered as causes for the observed Cepheid frequency-period distributions but fail to explain the similarities between the Cepheids, Wolf-Rayet and red supergiant luminosities.