Hot subdwarf binaries with white dwarf companions with orbital periods of less than two hours are progenitor candidates for massive single white dwarfs as well as a variety of thermonuclear explosions. Our aim is to determine the binary properties of the hot subdwarf -- white dwarf system ZTF, J000742. 62+480414. 51, model its future evolution, and characterize the brightening events seen in TESS photometry. Using data from ZTF and TESS, we performed a Lomb-Scargle analysis to find the orbital period and the period of the brightening events. Analysis of time-resolved spectroscopy was combined with light curve modeling to determine the effective temperature, surface gravity, and radius of the primary star, the masses of both stars, and to confirm the presence of an accretion disk. X-ray observations were performed with Swift, and MESA modeling was used to find the future evolution of the system. The kinematics of the system were also calculated. ZTF, J000742. 62+480414. 51 consists of an accreting 0. 48 = 108. 72 white dwarf with a 0. 42 ≈ 9 days. No X-rays were detected, with an upper limit on the X-ray luminosity of about 3,. The system lies in the Galactic thin disk and has an orbital period of P_ B-type hot subdwarf acting as a donor. The system exhibits SU UMa-type dwarf nova outbursts with a recurrence time of P_ out 31 -1 orb minutes. The system likely formed from a main-sequence binary with component masses and will likely merge into a single white dwarf, but a thermonuclear explosion cannot be ruled out. ZTF, J000742. 62+480414. 51 consists of a low-mass white dwarf actively accreting hydrogen-rich material from a B-type hot subdwarf, and it is the first hot subdwarf--white dwarf system discovered that produces dwarf nova outbursts.
Stringer et al. (Tue,) studied this question.