Can White Dwarf Asteroseismology Really Constrain the [TSUP]12[/TSUP]C(α, γ)[TSUP]16[/TSUP]O Reaction Rate?

Abstract

In light of the recent claims that the value of the C-O ratio at the center of DB white dwarfs can be determined from asteroseismological analyses, we have reexamined the available data (11 periods) for the best-studied star of the type, GD 358. We computed improved evolutionary models that combine evolution and diffusion and that lead to structurally different equilibrium configurations than used in the previous studies. In particular, we find that diffusion leads to the formation of a double-layered configuration that leaves very strong imprints on the theoretical period spectrum of models of GD 358. We find that our double-layered models with uniform core compositions are equally successful at explaining the GD 358 data as the single-layered models with variable core compositions used in recent studies. Given that single-layered DB models can no longer be justified when diffusion is properly taken into account, we conclude that reports of determinations of the central composition of GD 358 as well as related inferences on the astrophysically important 12C(α, γ)16O reaction rate are premature.