The Evolution and Pulsation of Crystallizing White Dwarf Stars (original) (raw)
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The effects of crystallization on the pulsations of white dwarf stars
2004
The theory of white dwarf crystallization lias been around for over forty years, yet there exists few direct observational tests to verify it. A littie over a decade has past since a possible testing-ground for the theory lias been discovered, the star BPM 37093, yet our ability to proceed with such tests using current methods is stiil under debate. This DAV star lias the cliaracteristic pulsations of tlie otliers of its type, yet it also lias a mass high enougli so that, by theoretical calculations, we expect tlie center to already be in tlie process of crystallizing, leading some to propose that the pulsations could serve as indicators of the crystallized fraction of tlie star. The validitidy of this daim, tlie use of current tecliniques and stellar knowledge. to determine tlie exact fraction of the star whicli is crystallized is tlie basis of this research. Using extensive, and careful modeling techniques, the relative importance of the crystallization as a parameter of pulsation...
1. Star Formation History and Physics from the White Dwarf Stars
We explore the physics of crystallization in the deep interiors of white dwarf stars using the color-magnitude diagram and luminosity function constructed from proper motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with the theory of crystallization of the ions in the interior of white dwarf stars and provide the first empirical evidence that the phase transition is first order: latent heat is released in the process of crystallization as predicted by van Horn (1968). We outline how this data can be used to observationally constrain the value of Γ ≡ ECoulomb/Ethermal near the onset of crystallization, the central carbon/oxygen abundance, and the importance of phase separation. Subject headings: white dwarfs — dense matter — equation of state
Uncovering the chemical structure of the pulsating low-mass white dwarf SDSS J115219.99+024814.4
Monthly Notices of the Royal Astronomical Society, 2021
Pulsating low-mass white dwarf (WD) stars are WDs with stellar masses between 0.30 and 0.45 M⊙ that show photometric variability due to gravity-mode pulsations. Within this mass range, they can harbour both a helium core and hybrid core, depending if the progenitor experienced helium-core burning during the pre-WD evolution. SDSS J115219.99+024814.4 is an eclipsing binary system where both components are low-mass WDs, with stellar masses of 0.362 ± 0.014 M⊙ and 0.325 ± 0.013 M⊙. In particular, the less-massive component is a pulsating star, showing at least three pulsation periods of ∼1314, ∼1069, and ∼582.9 s. This opens the way to use asteroseismology as a tool to uncover its inner chemical structure, in combination with the information obtained using the light-curve modelling of the eclipses. To this end, using binary evolutionary models leading to helium- and hybrid-core WDs, we compute adiabatic pulsations for ℓ = 1 and ℓ = 2 gravity modes with Gyre. We found that the pulsating...
We present a large bank of chemical profiles and pulsation periods suited for asteroseismological studies of ZZ Ceti (or DAV) variable stars. Our background equilibrium DA white dwarf models are the result of fully evolutionary computations that take into account the complete history of the progenitor stars from the ZAMS. The models are characterized by self-consistent chemical structures from the centre to the surface, and cover a wide range of stellar masses, effective temperatures, and H envelope thicknesses. We present dipole and quadrupole pulsation ggg-mode periods comfortably covering the interval of periods observed in ZZ Ceti stars. Complete tabulations of chemical profiles and pulsation periods to be used in asteroseismological period fits, as well as other quantities of interest, can be freely downloaded from our website (\url{http://www.fcaglp.unlp.edu.ar/evolgroup}