Cepheids in NGC 1866: a test for pulsational models

Abstract

We present non-linear theoretical results concerning the predicted pulsational behaviour of stellar models suitable for the sample of Cepheids belonging to the Large Magellanic Cloud (LMC) star cluster NGC 1866. The blue and red edges of the instability strip, transformed into the observed plane (V, B — V) by adopting current values for the distance modulus (DM = 18.57 mag according to Welch et al.) and for the reddening [E(B — V) = 0.06 mag according to Arp and Walker], are in agreement with the observed distribution of Cepheids in the quoted cluster. Moreover, the distribution of observational data in the Bailey diagram (V amplitude versus period) appears to be in agreement with theoretical predictions derived by adopting the luminosity level predicted by canonical evolutionary models. The role played by the direct ab initio integration of the coupling between pulsation and convection and by the input physics on the smoothness of light and velocity curves is briefly discussed.