Effects of extramixing processes on the periods of highorder gravity modes in mainsequen.pdfVIP

5 0 0 2 Comm. in Asteroseismology Vol. 144, 2003 t c O 1 2 1 Effects of “extra-mixing” processes on the periods of high-order gravity v modes in main-sequence stars 6 4 6 A. Miglio, J. Montalb´an, A. Noels 0 1 Institut d’Astrophysique et de G´eophysique de l’Universit´e de Li`ege, All´ee du 6 Aoˆut, 17 B-4000 Li`ege, 5 Belgium 0 / h Abstract p - In main-sequence stars, the chemical composition gradient that develops at the edge of the o convective core is responsible for a non-uniform period spacing of high-order gravity modes. r t In this work we investigate, in the case of a 1.6 M⊙ star, the effects on the period-spacing s of extra mixing processes in the core (such as diffusion and overshooting). a : v Effects of overshooting and diffusion on the central µ-profile i X We consider three models of a 1.6 M⊙ star on the main sequence: a model without any r “extra-mixing” process (model A), considering overshooting from the convective core (B) and a including helium diffusion (C). Though the central hydrogen abundance is the same (Xc = 0.3), the models have a different chemical composition profile near the outer edge of the convective core (see Fig. 1). Taking A as the reference model, we see that overshooting (B) displaces the location of the -gradient, whereas diffusion (C) leads to a smoother chemical composition profile. As shown in the lower panel of Fig. 1, such differences are also reflected in the behaviour of the Brunt-V¨ais¨al¨a frequency N that, in its turn, determines the properties of gravity modes. Effects on the period spacing In white dwarfs it has b