Can we reveal the core-chemical composition of ultra-massive white dwarfs through their magnetic fields?

Abstract

Ultra-massive white dwarfs ($1.05{\mathrm{M}}_{\odot }\lesssim {\mathrm{M}}_{\mathrm{WD}}$) are particularly interesting objects that allow us to study extreme astrophysical phenomena such as type Ia supernovae explosions and merger events. Traditionally, ultra-massive white dwarfs are thought to harbour oxygen-neon (ONe) cores. However, recent theoretical studies and new observations suggest that some ultra-massive white dwarfs could harbour carbon-oxygen (CO) cores. Although several studies have attempted to elucidate the core composition of ultra-massive white dwarfs, to date, it has not been possible to distinguish them through their observed properties. Here, we present a new method for revealing the core-chemical composition in ultra-massive white dwarfs that is based on the study of magnetic fields generated by convective mixing induced by the crystallization process. ONe white dwarfs crystallize at higher luminosities than their CO counterparts. Therefore, the study of magnetic ultra-massive white dwarfs in the particular domain where ONe cores have reached the crystallization conditions but CO cores have not, may provide valuable support to their ONe core-chemical composition, since ONe white dwarfs would display signs of magnetic fields and CO would not. We apply our method to eight white dwarfs with magnetic field measurements and we suggest that these stars are candidate ONe white dwarfs.

Accepted for publication in MNRAS Letters

References in corpus (21)

• Magnetic White Dwarfs
• New white dwarf stars in the Sloan Digital Sky Survey Data Release 10
• Binary Star Origin of High Field Magnetic White Dwarfs
• Magnetic fields in isolated and interacting white dwarfs
• A highly magnetised and rapidly rotating white dwarf as small as the Moon
• White dwarf evolutionary sequences for low-metallicity progenitors: The impact of third dredge-up
• A common origin of magnetism from planets to white dwarfs
• Evolutionary Models for the Remnant of the Merger of Two Carbon-Oxygen Core White Dwarfs
• New insight into the magnetism of degenerate stars from the analysis of a volume limited sample of white dwarfs
• An ultra-massive white dwarf with a mixed hydrogen-carbon atmosphere as a likely merger remnant
• Toward Precision Cosmochronology: A New C/O Phase Diagram for White Dwarfs
• The formation of ultra-massive carbon-oxygen core white dwarfs and their evolutionary and pulsational properties
• The Most Massive White Dwarfs in the Solar Neighborhood
• A population synthesis fitting of the $Gaia$ resolved white dwarf binary population within 100 pc
• Formation of ultra-massive carbon-oxygen white dwarfs from the merger of carbon-oxygen and helium white dwarf pairs
• The evolution of ultra-massive carbon oxygen white dwarfs
• Magnetic dynamos in white dwarfs -- II. Relating magnetism and pollution
• Asteroseismological analysis of the ultra-massive ZZ Ceti stars BPM~37093, GD~518, and SDSS~J0840+5222
• Magnetic dynamos in white dwarfs -- I. Explaining the dearth of bright intermediate polars in globular clusters
• Discovery of kilogauss magnetic fields on the nearby white dwarfs WD1105-340 and WD2150+591
• The pulsational properties of ultra-massive DB white dwarfs with carbon-oxygen cores coming from single-star evolution