The effect of diffusion on seismic models of SX Phoenicis stars

Diffusion processes, in particular the competing gravitational settling and radiative levitation, can significantly modify the distribution of chemical elements in stellar interiors and thus change the internal structure. These effects are especially relevant in stars with the weak envelope convection and relatively slow rotation, as they both cause efficient mixing. We study the effect of gravitational settling and radiative levitation on seismic models of SX Phoenicis (SX Phe) stars. In the case of these pulsators, due to their low metallicity, the convective transport efficiency is expected to be rather low. The sensitivity of seismic models to these processes can be particularly well captured in the case of stars pulsating in, at least, two radial modes, because their frequency ratio is confined to a narrow range. We select the five double-mode radially pulsating SX Phe stars in the globular cluster $\omega$ Cen and demonstrate how their seismic masses, metallicities and ages are affected by diffusive processes. The effect of rotation is also discussed.