Pulsation Models for Ultra-Low (Z=0.0004) Metallicity Classical Cepheids

Understand

Classical Cepheids are primary distance indicators playing a fundamental role in the calibration of the extragalactic distance scale.

• The possible dependence of their characteristic Period-Luminosity (PL) relation on chemical composition is still debated in the literature, and the behaviour of these pulsators at very low metallicity regimes is almost unexplored.
• In order to derive constraints on the application of the Period-Luminosity relation at low metal abundances, we investigate the properties of the few ultra-low metallicity (Z ~ 0.0004) Cepheids recently discovered in the Blue Compact Dwarf galaxy IZw18.
• To this purpose we have computed an updated and extended set of nonlinear convective models for Z=0.0004 and Y=0.24, spanning a wide range of stellar masses, and taking into account the evolutionary constraints for selected luminosity levels.