Céphéides: la relation période-luminosité

The Cepheids are relatively young, bright, periodic supergiant variable stars showing a correlation between their periods and luminosities. Since the beginning of the century the Cepheid Period -Luminosity relation has been the corner stone of distance determination, and of the measure of the correlation between the apparent relative expansion velocity to the relative distance (the Hubble constant, H₀). Using data obtained from the EROS project, we empirically found a small effect of metallicity on the Period-Luminosity relation which has important consequences for the inferred Cepheid distances and the determination of H₀.