The dependence of convective core overshooting on stellar mass

摘要

Context. Convective core overshooting extends the main-sequence lifetime of a star. Evolutionary tracks computed with overshooting are very different from those that use the classical Schwarzschild criterion, which leads to rather different predictions for the stellar properties. Attempts over the last two decades to calibrate the degree of overshooting with stellar mass using detached double-lined eclipsing binaries have been largely inconclusive, mainly because of a lack of suitable observational data. Aims. We revisit the question of a possible mass dependence of overshooting with a more complete sample of binaries, and examine any additional relation there might be with evolutionary state or metal abundance Z . Methods. We used a carefully selected sample of 33 double-lined eclipsing binaries strategically positioned in the H-R diagram with accurate absolute dimensions and component masses ranging from 1.2 to 4.4 M _(⊙) . We compared their measured properties with stellar evolution calculations to infer semi-empirical values of the overshooting parameter α _(ov) for each star. Our models use the common prescription for the overshoot distance d _(ov) = α _(ov) H _(p) , where H _(p) is the pressure scale height at the edge of the convective core as given by the Schwarzschild criterion, and α _(ov) is a free parameter. Results. We find a relation between α _(ov) and mass, which is defined much more clearly than in previous work, and indicates a significant rise up to about 2 M _(⊙) followed by little or no change beyond this mass. No appreciable dependence is seen with evolutionary state at a given mass, or with metallicity at a given mass although the stars in our sample span a range of a factor of ten in [Fe/H], from ?1.01 to + 0.01 .