Does convective core overshooting depend on stellar mass?

Abstract

Aims:We have selected 13 double-line eclipsing binary systems (DLEBS), strategically positioned in the HR diagram, to infer the mass dependence of the core overshooting parameter α_ov. Methods: In order to compare the data from these DLEBS with the theoretical predictions we computed four grids of evolutionary stellar models with variable amounts of core overshooting (α_ov = 0.0, 0.2, 0.4, and 0.6) in addition to those previously computed. In some particular cases specific models were computed for the precise observed masses. This procedure avoids interpolations and extrapolations, and only considers chemical compositions within the limits of the usual primordial helium abundance and enrichment law. Results: We used the ratio TR ≡ Teff 2/Teff 1 instead of the effective temperatures themselves as we consider it a much better constrained parameter. This is because it is directly derived from the analysis of light curves and is independent of calibrations, distances, and model atmospheres. In contrast to previous studies on the subject, we have found that standard models or models with moderate core overshooting (α_ov ≈ 0.2) are able to match the absolute dimensions of key DLEBS such as V380 Cyg or V453 Cyg. The resulting log M - α_ov diagram indicates that the dependence of α_ov on mass is more uncertain and less pronounced that previously established. This result is also consistent with the analysis of colour-magnitude diagrams for clusters and with previous comparisons of stellar models with larger samples of DLEBS. Figures 1-12 are only available in electronic form at http://www.aanda.org