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Abstract We consider the combined effects that overshooting and the12C(α,γ)16O 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 experimental12C(α,γ)16O reaction rate probability distribution function when overshooting is included in the evolution. These signatures hold because the resonating mantle region, encompassing ≃0.2M⊙in a typical ≃0.6M⊙WD model, still undergoes radiative helium burning during the evolution to a WD. Our specific models show two potential low-order adiabatic g-modes,g2andg6, that signalize the12C(α,γ)16O reaction rate probability distribution function. Both g-mode signatures induce average relative period shifts of ΔP/P= 0.44% and ΔP/P= 1.33% forg2andg6, respectively. We find thatg6is a trapped mode, and theg2period signature is inversely proportional to the12C(α,γ)16O reaction rate. Theg6period signature generally separates the slower and faster reaction rates, and has a maximum relative period shift of ΔP/P= 3.45%. We conclude that low-order g-mode periods from CO WDs may still serve as viable probes for the12C(α,γ)16O reaction rate probability distribution function when overshooting is included in the evolution.
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On the Impact of 22 Ne on the Pulsation Periods of Carbon–Oxygen White Dwarfs with Helium-dominated Atmospheres
Abstract We explore changes in the adiabatic low-order g-mode pulsation periods of 0.526, 0.560, and 0.729M⊙carbon–oxygen white dwarf models with helium-dominated envelopes due to the presence, absence, and enhancement of22Ne 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 without22Ne are fit to the observed periods and other properties. The rms residuals to the ≃150−400 s low-order g-mode periods are typically in the range ofσrms≲ 0.3 s, for a fit precision ofσrms/P≲ 0.3%. We find average relative period shifts of ΔP/P≃ ±0.5% for the low-order dipole and quadrupole g-mode pulsations within the observed effective temperature window, with the range of ΔP/Pdepending on the specific g-mode, abundance of22Ne, effective temperature, and the mass of the white dwarf model. This finding suggests a systematic offset may be present in the fitting process of specific white dwarfs when22Ne is absent. As part of the fitting processes involves adjusting the composition profiles of a white dwarf model, our study on the impact of22Ne can provide new inferences on the derived interior mass fraction profiles. We encourage routinely including22Ne mass fraction profiles, informed by stellar evolution models, to future generations of white dwarf model-fitting processes.
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- PAR ID:
- 10362058
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 910
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 24
- Size(s):
- Article No. 24
- Sponsoring Org:
- National Science Foundation
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