The influence of the equation of state on the zero-age main sequence and the Sun
Résumé
In the light of the uncertainty in the equation of state of stellar interiors, stellar and solar models were calculated using three different formalisms for the equation of state. The analysis includes a mixture of ideal gases using an artificial pressure-ionization device, an equation of state where pressure ionization is achieved by the confined-atom model; and an equation of state containing a large number of atomic and ionic species, with detailed internal partition functions, containing weighted occupation probabilities. The effect of these equations of state on the position of a star in the H-R diagram was examined. The result is either a displacement of the star on the zero-age main sequence (ZAMS) or, for masses lower than 0.7M a change in the slope of the ZAMS. The usual calibration procedure was carried out in order to obtain the initial He abundance Y of the solar model.