Measuring 12C(α, γ)16O from White Dwarf Asteroseismology

During helium burning in the core of a red giant, the relative rates of the 3α and 12C(α, γ)16O reactions largely determine the final ratio of carbon to oxygen in the resulting white dwarf star. The uncertainty in the 3α reaction at stellar energies due to the extrapolation from high-energy laboratory measurements is relatively small, but this is not the case for the 12C(α, γ)16O reaction. Recent advances in the analysis of asteroseismological data on pulsating white dwarf stars now make it possible to obtain precise measurements of the central ratio of carbon to oxygen, providing a more direct way to measure the 12C(α, γ)16O reaction rate at stellar energies. We assess the systematic uncertainties of this approach and quantify small shifts in the measured central oxygen abundance originating from the observations and from model settings that are kept fixed during the optimization. Using new calculations of white dwarf internal chemical profiles, we find a rate for the 12C(α, γ)16O reaction that is significantly higher than most published values. The accuracy of this method might improve as we modify some of the details of our description of white dwarf interiors that were not accessible through previous model-fitting methods.