2023ApJ...959..114K

We present an analysis of new and archival data to the 20.506 minute LISA verification binary J052610.42+593445.32 (J0526+5934). Our joint spectroscopic and photometric analysis finds that the binary contains an unseen M₁ = 0.89 ± 0.11 M_⊙ CO-core white dwarf primary with an M₂ = 0.38 ± 0.07 M_⊙ post-core-burning subdwarf, or low-mass white dwarf, companion. Given the short orbital period and relatively large total binary mass, we find that LISA will detect this binary with signal-to-noise ratio 44 after 4 yr of observations. J0526+5934 is expected to merge within 1.8 ± 0.3 Myr and likely result in a D⁶ scenario Type Ia supernova or form a He-rich star that will evolve into a massive single white dwarf.