On The Impact Of 22Ne On The Pulsation Periods Of Carbon-Oxygen White Dwarfs With Helium Dominated Atmospheres

TL;DR

This study investigates how the presence of $^{22}$Ne affects the pulsation periods of carbon-oxygen white dwarfs with helium atmospheres, revealing systematic shifts that impact model fitting accuracy.

Contribution

It demonstrates the significance of including $^{22}$Ne in white dwarf models to improve pulsation period fits and interior composition inferences.

Findings

$^{22}$Ne causes $ ext{~} ext{0.5 ext{ extperthousand}}$ shifts in pulsation periods.

Neglecting $^{22}$Ne can lead to systematic offsets in white dwarf modeling.

Including $^{22}$Ne improves the accuracy of interior composition estimates.

Abstract

We explore changes in the adiabatic low-order g-mode pulsation periods of 0.526, 0.560, and 0.729 M$_\odot$ carbon-oxygen white dwarf models with helium-dominated envelopes due to the presence, absence, and enhancement of $^{22}$Ne in the interior. The observed g-mode pulsation periods of such white dwarfs are typically given to 6$-$7 significant figures of precision. Usually white dwarf models without $^{22}$Ne are fit to the observed periods and other properties. The root-mean-square residuals to the $\simeq$ 150$-$400 s low-order g-mode periods are typically in the range of $\sigma_{rms}$ $\lesssim$ 0.3 s, for a fit precision of $\sigma_{rms}/ P$ $\lesssim$ 0.3 %. We find average relative period shifts of $\Delta P/P$ $\simeq$ $\pm$ 0.5 % for the low-order dipole and quadrupole g-mode pulsations within the observed effective temperature window, with the range of $\Delta P/P$ depending on the specific g-mode, abundance of $^{22}$Ne, effective temperature, and mass of the white dwarf model. This finding suggests a systematic offset may be present in the fitting process of specific white dwarfs when $^{22}$Ne is absent. As part of the fitting processes involves adjusting the composition profiles of a white dwarf model, our study on the impact of $^{22}$Ne can provide new inferences on the derived interior mass fraction profiles. We encourage routinely including $^{22}$Ne mass fraction profiles, informed by stellar evolution models, to future generations of white dwarf model fitting processes.