  Convective core overshooting extends the main-sequence lifetime of a star.
Evolutionary tracks computed with overshooting are quite 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 due to a
lack of suitable observational data. Here 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. We use 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 solar masses. We
compare their measured properties with stellar evolution calculations to infer
semi-empirical values of the overshooting parameter alpha(ov) for each star.
Our models use the common prescription for the overshoot distance d(ov) =
alpha(ov) Hp, where Hp is the pressure scale height at the edge of the
convective core as given by the Schwarzschild criterion, and alpha(ov) is a
free parameter. We find a relation between alpha(ov) and mass that is defined
much more clearly than in previous work, and indicates a significant rise up to
about 2 solar masses 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 despite the fact that the stars in our sample span
a range of a factor of ten in [Fe/H], from -1.01 to +0.01.

Solar and Stellar Astrophysics