Linear theory period ratios for surface helium enhanced doublemode Cepheids.
Abstract
Linearnonadiabatictheory period ratios for models of doublemode Cepheids with their two periods between 1 and 7 days have been computed by assuming differing amounts and depths of surface helium enhancement. Evolutiontheory masses and luminosities are found to be consistent with the observed periods. All models give a period ratio of approximately 0.70 as observed for the 11 known variables, contrary to previous theoretical conclusions. The composition structure that best fits the period ratios has the helium mass fraction in the outer 0.001 of the stellar mass (T no more than 250,000 K) as 0.65, similar to a previous model for the triplemode pulsator AC And. This enrichment can be established by a Cepheid wind and downward invertedmugradientinstability mixing in the lifetime of these lowmass classical Cepheids.
 Publication:

The Astrophysical Journal
 Pub Date:
 June 1979
 DOI:
 10.1086/182972
 Bibcode:
 1979ApJ...230L.109C
 Keywords:

 Cepheid Variables;
 Helium;
 Pulsars;
 Stellar Evolution;
 Stellar Mass;
 Astrophysics;
 Stellar Structure;
 Stellar Winds;
 Astrophysics;
 Cepheids:Models;
 Cepheids:Periods