Seismic Signatures of the 12C(α, γ)16O Reaction Rate in White Dwarf Models with Overshooting

Abstract

We consider the combined effects that overshooting and the ^12 C( α , γ ) ^16 O reaction rate have on variable white dwarf (WD) stellar models. We find that carbon–oxygen (CO) WD models continue to yield pulsation signatures of the current experimental ^12 C( α , γ ) ^16 O reaction rate probability distribution function when overshooting is included in the evolution. These signatures hold because the resonating mantle region, encompassing ≃0.2 M _⊙ in a typical ≃0.6 M _⊙ WD model, still undergoes radiative helium burning during the evolution to a WD. Our specific models show two potential low-order adiabatic g-modes, g _2 and g _6 , that signalize the ^12 C( α , γ ) ^16 O reaction rate probability distribution function. Both g-mode signatures induce average relative period shifts of Δ P / P = 0.44% and Δ P / P = 1.33% for g _2 and g _6 , respectively. We find that g _6 is a trapped mode, and the g _2 period signature is inversely proportional to the ^12 C( α , γ ) ^16 O reaction rate. The g _6 period signature generally separates the slower and faster reaction rates, and has a maximum relative period shift of Δ P / P = 3.45%. We conclude that low-order g-mode periods from CO WDs may still serve as viable probes for the ^12 C( α , γ ) ^16 O reaction rate probability distribution function when overshooting is included in the evolution.

Keywords

• Asteroseismology
• Nuclear astrophysics
• White dwarf stars
• Stellar physics