Surface abundances of Am stars as a constraint on rotational mixing Olivier Richard 1,2, Suzanne Talon 2, Georges Michaud 2 1 GRAAL UMR5024, Université Montpellier II, Montpellier, France 2 Département de physique, Université de Montréal, Montréal, Canada

Am stars Montréal Models Results Surface abundances of Am stars as a constraint on rotational mixing

Statistics suggest all non-magnetic stars with V<80 km/s Recent observations in open clusters Mg~ normal Al, Si, S: ~normal or slight overabundance Ca ~ normal or underabundant Ni and Fe overabundant Am Stars

Burger’s equations 2 equations for each species (28 in the code) Solved for each mesh points (~1500) and at each time step (~1000)

Radiative accelerations 1.5 GigaBytes of data ; OPAL (1996) –Integration over fraction of photons given to i at each frequency Expression used in evolution calculations

Mixing model Simplest version of the turbulent diffusion coefficient obtained from self-consistent treatment of the meridional circulation following Zahn (1992) Mixing added to the code as a diffusion process with a parametric mixing diffusion coefficient:

Mixing model Simplest version of the turbulent diffusion coefficient obtained from self-consistent treatment of the meridional circulation following Zahn (1992) Mixing added to the code as a diffusion process with a parametric mixing diffusion coefficient:

Computed models Models of 1.7 and 1.9 solar masses With mixing coefficient corresponding to surface velocity of 50 km/s (V50), 15 km/s (V15), and 5 km/s (V5, V5N) Richer et al. (2000) 1.9R300-2 and 1.9R1k- 2 models

Effective temperature and surface gravity evolution

Radiative acceleration in the 1.9 solar masses models

Abundance profiles at 800 Myr Model 1.9V5 r 1 0

Abundance evolution in the 1.9 solar masses models

The Praesepe star HD73045

Conclusion In the mixing model the turbulence seems to be too strong to allow the Am phenomenon to occur at a reasonable velocity Need of self-consistent abundance determination for a lot of chemical species in stars of different ages and metallicity