The seismic properties of low-mass He-core white dwarf stars

Abstract

We present here a detailed pulsational study applied to low-mass He-core white dwarfs, based on full evolutionary models representative of these objects. The background stellar models on which our pulsational analysis was carried out were derived by taking into account the complete evolutionary history of the progenitor stars, with special emphasis on the diffusion processes acting during the white dwarf cooling phase. We computed nonradial $g$-modes to assess the dependence of the pulsational properties of these objects with stellar parameters such as the stellar mass and the effective temperature, and also with element diffusion processes. We also performed a g- and p-mode pulsational stability analysis on our models and found well-defined blue edges of the instability domain, where these stars should start to exhibit pulsations. We found substantial differences in the seismic properties of white dwarfs with $M_{\ast }\gtrsim 0.20M_{\odot }$ and the extremely low-mass (ELM) white dwarfs ($M_{\ast }\lesssim 0.20M_{\odot }$). Specifically, $g$-mode pulsation modes in ELM white dwarfs mainly probe the core regions and are not dramatically affected by mode-trapping effects by the He/H interface, whereas the opposite is true for more massive He-core white dwarfs. We found that element diffusion processes substantially affects the shape of the He/H chemical transition region, leading to non-negligible changes in the period spectrum of low-mass white dwarfs. Our stability analysis successfully predicts the pulsations of the only known variable low-mass white dwarf (SDSS J184037.78+642312.3), and also predicts both $g$- and $p$-mode pulsational instabilities in a significant number of known low-mass and ELM white dwarfs.

14 pages, 15 figures, 2 tables. To be published in Astronomy & Astrophysics

References in corpus (8)

• Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models
• Pulsating White Dwarf Stars and Precision Asteroseismology
• White Dwarf Mass Distribution in the SDSS
• The ELM Survey. I. A Complete Sample of Extremely Low Mass White Dwarfs
• Asteroseismic inferences on GW Vir variable stars in the frame of new PG 1159 evolutionary models
• New nonadiabatic pulsation computations on full PG1159 evolutionary models: the theoretical GW Vir instability strip revisited
• Seismological studies of ZZ Ceti stars. I. The model grid and the application to individual stars
• The Discovery of a Companion to the Lowest Mass White Dwarf

Cited by in corpus (30)

• Hot subluminous stars
• New evolutionary sequences for extremely low mass white dwarfs: Homogeneous mass and age determinations, and asteroseismic prospects
• New white dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 12
• Spectroscopic analysis of DA white dwarfs with 3D model atmospheres
• Pulsating white dwarfs: new insights
• White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14
• The ELM Survey. V. Merging Massive White Dwarf Binaries
• Forward asteroseismic modeling of stars with a convective core from gravity-mode oscillations: parameter estimation and stellar model selection
• Formation of Extremely Low-mass White Dwarfs in Double Degenerates
• A new class of pulsating white dwarf of extremely low mass: the fourth and fifth members
• Asteroseismological study of massive ZZ Ceti stars with fully evolutionary models
• Discovery of pulsations, including possible pressure modes, in two new extremely low mass, He-core white dwarfs
• PSR J1738+0333: The First Millisecond Pulsar + Pulsating White Dwarf Binary
• A Refined Search for Pulsations in White Dwarf Companions to Millisecond Pulsars
• Discovery of 74 new bright ZZ Ceti stars in the first three years of TESS
• Pulsating low-mass white dwarfs in the frame of new evolutionary sequences: I. Adiabatic properties
• A revisit of PSR J1909$-$3744 with 15-year high-precision timing
• Pulsating low-mass white dwarfs in the frame of new evolutionary sequences: III. The pre-ELM white dwarf instability strip
• White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 16
• An eccentric binary millisecond pulsar with a helium white dwarf companion in the Galactic Field
• Hydrogen in hot subdwarfs formed by double helium white dwarf mergers
• Short-period $g$-mode pulsations in low-mass white dwarfs triggered by H shell burning
• Pulsating low-mass white dwarfs in the frame of new evolutionary sequences: II. Nonadiabatic analysis
• Asteroseismic test of rotational mixing in low-mass white dwarfs
• Pulsating low-mass white dwarfs in the frame of new evolutionary sequences: IV. The secular rate of period change
• Pulsating low-mass white dwarfs in the frame of new evolutionary sequences VI. Thin H-envelope sequences and asteroseismology of ELMV stars revisited
• Pulsating low-mass white dwarfs in the frame of new evolutionary sequences: V. Asteroseismology of ELMV white dwarf stars
• A Model of the Pulsating Extremely Low-Mass White Dwarf Precursor WASP 0247-25B
• The McDonald Observatory search for pulsating sdA stars: asteroseismic support for multiple populations
• Searching for new variable white dwarfs: The discovery of the three new pulsating and three new binary systems