Asteroseismic study of helium and heavy element diffusion in solar-type stars^*

¹ Department of Astronomy, Beijing Normal University, Beijing 100875, PR China e-mail: gaining@mail.bnu.edu.cn; bisl@bnu.edu.cn
² Department of Physics, Dezhou University, Dezhou 253023, PR China e-mail: tyk450@163.com
³ Department of Astronomy, Yale University, New Haven, CT06520, USA e-mail: li@astro.yale.edu

Received: 3 May 2009
Accepted: 18 September 2009

Abstract

Aims. Element diffusion is a basic physical element transport mechanism which induces the redistribution of chemical elements. Using the asteroseismic method, we study the effects of helium and heavy element diffusion on the internal structure and stellar evolution of solar-type stars. We also provide asteroseismic parameters for a grid of models which would be useful for direct comparison with the Kepler mission observations.

Methods. We construct a grid of solar-type stellar models with various masses (from 0.8  to 1.2 ) and metallicities (Z_i = 0.03, 0.025, 0.02, 0.015, 0.01, 0.005) with and without helium and heavy element diffusion. We compute “second differences” and “small separations” of the solar-metallicity models (Z_i = 0.02) to analyze the effects of diffusion on the convection zone, helium abundance and the evolutionary sequence of the star. In order to study the asteroseismic property of models with and without diffusion, we compute the p-mode oscillation frequencies of low-degree modes for a grid of models and construct the asteroseismic diagram.

Results. We find that the element diffusion could speed up the evolution of the star, especially in the main sequence. The results show that it could enlarge the convective core and change the base of the convection envelope. In addition, the helium and heavy element diffusion make the models evolve to lower large and small separations in the asteroseismic diagram. This effect is more efficient at lower metallicity.