Abstract
Abstract We explore changes in the adiabatic low-order g-mode pulsation periods of 0.526, 0.560, and 0.729 M ⊙ carbon–oxygen white dwarf models with helium-dominated envelopes due to the presence, absence, and enhancement of 22Ne 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 22Ne 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 of σ rms ≲ 0.3 s, for a fit precision of σ rms/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/P depending on the specific g-mode, abundance of 22Ne, 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 when 22Ne is absent. As part of the fitting processes involves adjusting the composition profiles of a white dwarf model, our study on the impact of 22Ne can provide new inferences on the derived interior mass fraction profiles. We encourage routinely including 22Ne mass fraction profiles, informed by stellar evolution models, to future generations of white dwarf model-fitting processes.
Highlights
Photons emitted from stellar surfaces and neutrinos released from stellar interiors may not directly reveal all that we want to know about the internal constitution of the stars
Camisassa et al (2016) analyzed the impact of 22Ne on the sedimentation and pulsation properties of H-dominated atmosphere white dwarfs (WDs) with masses of 0.528, 0.576, 0.657, and 0.833 Me. These WD models result from Z = 0.02 nonrotating evolutionary models that start from the zero-age main sequence (ZAMS) and are evolved through the core-hydrogen and corehelium burning, thermally pulsing asymptotic giant branch (AGB), and post-AGB phases
We explore the impact of 22Ne on the adiabatic low-order g-mode pulsation periods of carbon–oxygen white dwarf (CO WD) models with a He-dominated atmosphere as the models cool through the range of observed DBV effective temperatures
Summary
Photons emitted from stellar surfaces and neutrinos released from stellar interiors may not directly reveal all that we want to know about the internal constitution of the stars. Camisassa et al (2016) analyzed the impact of 22Ne on the sedimentation and pulsation properties of H-dominated atmosphere WDs (i.e., the DAV class of WD) with masses of 0.528, 0.576, 0.657, and 0.833 Me These WD models result from Z = 0.02 nonrotating evolutionary models that start from the ZAMS and are evolved through the core-hydrogen and corehelium burning, thermally pulsing asymptotic giant branch (AGB), and post-AGB phases. Giammichele et al (2018) analyzed in their supplemental material the effect of 22Ne on the pulsation periods of a 0.570 Me template-based model for the DB WD KIC 08626021 They considered a model consisting of pure oxygen core surrounded by a pure helium envelope with the same mass and effective temperature equal to those inferred for KIC 08626021. In Appendix A, we study the robustness of our results with respect to mass and temporal resolution, and in Appendix B we discuss in greater depth some of the input physics
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