Uncovering the chemical structure of the pulsating low-mass white dwarf SDSS J115219.99+024814.4

Abstract

Pulsating low-mass white dwarf stars are white dwarfs with stellar masses between 0.30 M and 0.45 M that show photometric variability due to gravity-mode pulsations. Within this mass range, they can harbour both a helium-and hybrid-core, depending if the progenitor experienced helium-core burning during the pre-white dwarf evolution. SDSS J115219.99+024814.4 is an eclipsing binary system where both components are low-mass white dwarfs, 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 s, ∼1069 s 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 white dwarfs, we compute adiabatic pulsations for ℓ = 1 and ℓ = 2 gravity modes with Gyre. We found that the pulsating component of the SDSS J115219.99+024814.4 system must have a hydrogen envelope thinner that the value obtained from binary evolution computations, independently of the inner composition. Finally, from our asteroseismological study, we find a best fit model characterised by T eff = 10 917 K, M=0.338 M , M H = 10 −6 M with the inner composition of a hybrid WD.

Masses of White Dwarf Binary Companions to Type Ia Supernovae Measured from Runaway Velocities

“…• For M don < 0.45 M , we interpolate based on the helium-core WD model grid of Althaus et al (2013), which reliably covers a mass range of about 0.2-0.43 M for T eff ≤ 30,000 K. It is also possible that a significant fraction of WDs in compact binaries with M don ≈ 0. He cores (Zenati et al 2019;Kupfer et al 2020a,b;Bauer & Kupfer 2021;Schwab & Bauer 2021;Romero et al 2021). For simplicity, we do not include this possibility in our plots in this paper, but it should be noted that some WDs in this mass range could have somewhat more compact cores than the He models presented here.…”