Related papers: Hot White Dwarf Donors in Ultracompact X-Ray Binar…

We present the discovery of the second binary with a Roche lobe-filling hot subdwarf transferring mass to a white dwarf (WD) companion. This 56 minute binary was discovered using data from the Zwicky Transient Facility. Spectroscopic…

We discuss the mass-radius (M-R) relations for low-mass (M<0.1 Msun) white dwarfs (WDs) of arbitrary degeneracy and evolved (He, C, O) composition. We do so with both a simple analytical model and models calculated by integration of…

Binary evolution predicts a population of helium core (M < 0.5 Msol) white dwarfs (WDs) that are slowly accreting hydrogen-rich material from low mass main sequence or brown dwarf donors with orbital periods less than four hours. Four…

We examine a number of evolutionary scenarios for the recently discovered class of accretion-powered millisecond X-ray pulsars in ultracompact binaries, including XTE J0929-314 and XTE J1751-305, with orbital periods of 43.6 and 42.4…

Binaries consisting of a hot subdwarf star and an accreting white dwarf (WD) are sources of gravitational wave radiation at low frequencies and possible progenitors of type Ia supernovae if the WD mass is large enough. Here, we report the…

Evolution of a large part of low-mass X-ray binaries (LMXBs) leads to the formation of rapidly rotating pulsars with a helium white dwarf (He WD) companion. Observations indicate that some He WDs in binary pulsar systems are ultracool (with…

The new-found prevalence of extremely low mass (ELM, Mhe<0.2 Msun) helium white dwarfs (WDs) in tight binaries with more massive WDs has raised our interest in understanding the nature of their mass transfer. Possessing small (Menv~1e-3…

We calculate the stellar evolution of both white dwarfs (WDs) in AM CVn binaries with orbital periods of $P_{\mathrm{orb}} \approx 5-70$ minutes. We focus on the cases where the donor starts as a $M_{\mathrm{He}} < 0.2 \, M_{\odot}$ Helium…

ZTF J213056.71+442046.5 is the prototype of a small class of recently discovered compact binaries composed of a white dwarf and a hot subdwarf that fills its Roche-lobe. Its orbital period of only 39 min is the shortest known for the…

We report the discovery of the first short period binary in which a hot subdwarf star (sdOB) fills its Roche lobe and started mass transfer to its companion. The object was discovered as part of a dedicated high-cadence survey of the…

Binary millisecond pulsars (BMSPs) are thought to have evolved from low-mass X-ray binaries (LMXBs). If the mass transfer in LMXBs is driven by nuclear evolution of the donor star, the final orbital period is predicted to be well correlated…

Tight binaries of helium white dwarfs (He WDs) orbiting millisecond pulsars (MSPs) will eventually "merge" due to gravitational damping of the orbit. The outcome has been predicted to be the production of long-lived ultra-compact X-ray…

Accretion-induced collapse of massive white dwarfs (WDs) has been proposed to be an important channel to form binary millisecond pulsars (MSPs). Recent investigations on thermal timescale mass transfer in WD binaries demonstrate that the…

We have performed detailed numerical calculations of the non-conservative evolution of close X-ray binary systems with intermediate-mass (2.0-6.0 M_sun) donor stars and a 1.3 M_sun accreting neutron star. We calculated the thermal response…

Binary systems of a hot subdwarf B (sdB) star + a white dwarf (WD) with orbital periods less than 2-3 hours can come into contact due to gravitational waves and transfer mass from the sdB star to the WD before the sdB star ceases nuclear…

We study the formation of neon-enriched donor stars in ultracompact X-ray binaries (orbital periods P<80 min) and show that their progenitors have to be low-mass (0.3 - 0.4 solar mass) ``hybrid'' white dwarfs (with CO cores and thick helium…

We have performed detailed numerical calculations of the non-conservative evolution of close binary systems with low-mass (1.0-2.0 M_sun) donor stars and a 1.3 M_sun accreting neutron star. Rather than using analytical expressions for…

We report the results from follow-up observations of two Roche-lobe filling hot subdwarf binaries with white dwarf companions predicted to have accretion disks. ZTF J213056.71+442046.5 (ZTF J2130) with a 39-minute period and ZTF…

A large number of low-mass (< 0.20 M_sun) helium white dwarfs (He WDs) have recently been discovered. The majority of these are orbiting another WD or a millisecond pulsar (MSP) in a close binary system; a few examples are found to show…

We present LAMOST J0140355+392651 (hereafter J0140), a close ($P_{\rm orb} = 3.81$ hours) binary containing a bloated, low-mass ($M \approx 0.15 M_{\odot}$) proto-white dwarf (WD) and a massive ($M\approx 0.95\,M_{\odot}$) WD companion. The…