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

TL;DR

This paper analyzes the double-degenerate system NLTT 12758, revealing a rapidly spinning magnetic white dwarf and a non-magnetic companion, with implications for supernova and neutron star formation.

Contribution

It provides detailed measurements of the system's orbital and stellar parameters, highlighting the potential for future explosive events due to mass transfer.

Findings

Magnetic white dwarf has a 23-minute spin period.

Total system mass exceeds the Chandrasekhar limit.

System will likely produce a supernova or neutron star upon contact.

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.