Asteroseismology of the DBV star CBS 114

Abstract

Asteroseismology is an unique and powerful tool to detect the internal structure of stars. CBS 114 is the sixth known pulsating DBV star. It was observed by Handler, Metcalfe, & Wood at South African Astronomical Observatory over 3 weeks in 2001. Then, it was observed by Metcalfe et al. at Bohyunsan Optical Astronomy Observatory and McDonald Observatory respectively for 7 nights in 2004. Totally 2 triplets, 4 doublets, and 5 singlets were identified. The frequency splitting values are very different, from 5.2 µHz to 11.9 µHz, which may reflect differential rotations. We evolve grids of white dwarf models by MESA. Cores, added with He/C envelopes, of those white dwarf models are inserted into WDEC to evolve grids of DBV star models. With those DBV star models, we calculate eigenperiods. Those calculated periods are used to fit observed periods. A best-fitting model is selected. The parameters are T ef f = 25000 K, M * = 0.740 M ⊙ , and log(M He /M * ) = -4.5. With the massive stellar mass, the effective temperature is close to previous spectroscopic result. In addition, kinetic energy distributions are calculated for the best-fitting model. We find that the observed modes with large frequency splitting values are fitted by the calculated modes with much kinetic energy distributed in C/O core. After preliminary analysis, we suggest that the C/O core may rotate at least 2 times faster than the helium layer for CBS 114.

Constraining the parameter space of branon dark matter using white dwarf stars

“…White dwarf (WD) stars are old compact objects that mark the final evolutionary stage of the vast majority of the stars [33,34]. Indeed more than 95, perhaps up to 98 per cent of all stars will die as white dwarfs [35].…”

“…Since there are no thermonuclear reactions for WD, these objects are cooling down by eradiating. Along the cooling track, there are basically three classes of white stars, namely DAV stars with an effective temperature around T ef f ∼ 12 × 10 3 K, DBV stars with an effective temperature around T ef f ∼ 25 × 10 3 K, and DOV white dwarfs with an effective temperature around T ef f ∼ 100 × 10 3 K [34]. Here we shall consider a typical white dwarf star of the DBV type with mass M ⋆ ∼ M ⊙ = 2 × 10 30 kg, radius R ⋆ ∼ R earth ≃ 0.01R ⊙ ≃ 7 × 10 3 km, temperature T ∼ 25 × 10 3 K, matter density ρ ∼ 10 10 kg/m 3 and pressure P ∼ 10 23 N/m 2 , where M ⊙ and R ⊙ are the solar mass and solar radius respectively.…”

“…We work in units in which the speed of light in vacuum c, the Boltzmann constant k B and the reduced Planck mass are set to unity, c = k B = = 1. In these units all dimensionful quantities are measured in GeV, and we make use of the conversion rules 1m = 5.068 × 10 White dwarf (WD) stars are old compact objects that mark the final evolutionary stage of the vast majority of the stars [33,34]. Indeed more than 95, perhaps up to 98 per cent of all stars will die as white dwarfs [35].…”

White dwarf cooling via gravity portals

“…White dwarf stars are old compact objects that mark the final evolutionary stage of the vast majority of the stars [51,52]. Indeed more than 95%, perhaps up to 98% of all stars, will die as white dwarfs [53].…”