Two new young, wide magnetic + non-magnetic double-degenerate binary systems

Abstract

Abridged: We report the discovery of two, new, rare, wide, double-degenerate binaries that each contain a magnetic and a non-magnetic star. The components of SDSSJ092646.88+132134.5 + J092647.00+132138.4 and SDSSJ150746.48+521002.1 + J150746.80+520958.0 have angular separations of only 4.6 arcsec (a~650AU) and 5.1 arcsec (a~750AU), respectively. They also appear to share common proper motions. Follow-up optical spectroscopy reveals each system to consist of a DA and a H-rich high-field magnetic white dwarf (HFMWD). Our measurements of the effective temperatures and the surface gravities of the DA components reveal both to have larger masses than are typical of field white dwarfs. By assuming that these degenerates have evolved essentially as single stars, due to their wide orbital separations, we use them to place limits on the total ages of our stellar systems. These argue that in each case the HFMWD is probably associated with an early type progenitor (M_init > 2M_solar). We find that the cooling time of SDSSJ150746.80+520958.0 (DAH) is somewhat lower than might be expected had it followed the evolutionary path of a typical single star. This mild discord is in the same sense as that observed for two of the small number of other HFMWDs for which progenitor mass estimates have been made, REJ0317-853 and EG59. The mass of the other DAH, SDSSJ092646.88+132134.5, appears to be smaller than expected on the basis of single star evolution. If this object was/is a member of a hierarchical triple system it may have experienced greater mass loss during an earlier phase of its life as a result of it having a close companion. The large uncertainties on our estimates of the parameters of the HFMWDs suggest a larger sample of these objects is required to firmly identify any trends in their inferred cooling times and progenitor masses.

Accepted for MNRAS

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• Constraints on the Initial-Final Mass Relation from Wide Double White Dwarfs
• A magnetic white dwarf in a detached eclipsing binary
• Testing White Dwarf Age Estimates using Wide Double White Dwarf Binaries from Gaia EDR3
• Further investigation of white dwarfs in the open clusters NGC2287 and NGC3532
• Magnetic white dwarfs with debris discs
• A fast spinning magnetic white dwarf in the double-degenerate, super-Chandrasekhar system NLTT 12758
• Component masses of young, wide, non-magnetic white dwarf binaries in the SDSS DR7
• A Magnetic White Dwarf with Five H$\alpha$ Components
• The progenitors of magnetic white dwarfs in open clusters
• Common Proper Motion Wide White Dwarf Binaries Selected From The Sloan Digital Sky Survey