New strong evidence for the importance of convective overshooting in intermediate-mass stars

Abstract

Major differences between current series of stellar evolution calculations concern their opacities and treatment of convection. Accurate mass, radius, luminosity, and abundance data from eclipsing binaries now allow significant conclusions on these differences: Binary stars with small convective cores (M/M 0 « 1.2) are very well fitted by standard models using Los Alamos (but not Cox-Stewart) opacities. However, at just slightly larger masses (1.5 < 2.5), the moderately evolved binaries clearly require convective overshooting for a satisfactory fit. Precise radial velocities for F-type turnoff stars in IC 4651 and NGC 3680 not only confirm the signatures of overshooting observed in these clusters but also show that any such firm conclusions require proper identification of binaries and nonmembers. We conclude that standard (and some overshooting) models are inconsistent with current precise data for intermediate-mass stars. Among the consequences of rejecting the older models, we point out that ages for stars younger than «4 Gyr will increase by up to 50%-100%.