A fast spinning magnetic white dwarf in the double-degenerate, super-Chandrasekhar system NLTT 12758

Abstract

We present an analysis of the close double degenerate NLTT 12758, which is comprised of a magnetic white dwarf with a field of about 3.1 MG and an apparently non-magnetic white dwarf. We measured an orbital period of 1.154 days and found that the magnetic white dwarf is spinning around its axis with a period of 23 minutes. An analysis of the atmospheric parameters has revealed that the cooling ages of the two white dwarfs are comparable, suggesting that they formed within a short period of time from each other. Our modelling indicates that the non-magnetic white dwarf is more massive (M=0.83 M_sun) than its magnetic companion (M=0.69 M_sun) and that the total mass of the system is higher than the Chandrasekhar mass. Although the stars will not come into contact over a Hubble time, when they do come into contact, dynamically unstable mass transfer will take place leading to either an accretion induced collapse into a rapidly spinning neutron star or a Type Ia supernova.

Accepted for publication in MNRAS

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• Signs of Binary Evolution in 7 Magnetic DA White Dwarfs
• A super-Chandrasekhar mass type Ia supernova progenitor at 49 pc set to detonate in 23 Gyr
• Exploring Temperature Influences on Gravitational Wave Production in Binary White Dwarfs
• Magnetic dynamos in white dwarfs -III: explaining the occurrence of strong magnetic fields in close double white dwarfs