Related papers: EVR-CB-001: An evolving, progenitor, white dwarf c…

We present the discovery and multi-wavelength characterisation of VVV J1438-6158 AB, a new field wide-binary system consisting of a 4.6(+5.5-2.4) Gyr and Teff = 9500+/-125 K DA white dwarf (WD) and a Teff = 2400+/-50 K M8 ultracool dwarf…

Hot subdwarf B stars (sdBs) are evolved core helium-burning stars with very thin hydrogen envelopes. In order to form an sdB, the progenitor has to lose almost all of its hydrogen envelope right at the tip of the red giant branch. In close…

Subdwarf B (sdB) stars (and related sdO/sdOB stars) are believed to be helium core-burning objects with very thin hydrogen-rich envelopes. In recent years it has become increasingly clear from observational surveys that a large fraction of…

ATLAS J1138-5139 is a newly detected ultra-compact double white dwarf (DWD) system which is composed of a $1.02\,M_{\odot}$ carbon-oxygen white dwarf (CO WD) and a $0.24\,M_{\odot}$ helium (He) WD with an orbital period of about 27.68 min,…

We report the discovery of a bright (V=11.6 mag) eclipsing hot subdwarf binary of spectral type B with a late main sequence companion from the All Sky Automated Survey (ASAS 102322-3737.0). Such systems are called HW Vir stars after the…

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 +…

A detailed analysis of halo white dwarf candidates is presented, which is based on model atmosphere fits to observed energy distributions built from photoelectric or photographic magnitudes. Most of the candidates identified in reduced…

We present an analysis of LAMOST J171013.211+532646.04 (hereafter J1710), a binary system comprising a hot subdwarf B star (sdB) and a white dwarf (WD) companion. Multi-epoch spectroscopy reveals an orbital period of 109.20279 minutes,…

Extremely low-mass white dwarfs (ELM WDs) are helium WDs with a mass less than $\sim$$0.3\rm\;M_\odot$. Most ELM WDs are found in double degenerates (DDs) in the ELM Survey led by Brown and Kilic. These systems are supposed to be…

We present radial velocity observations of four extremely low-mass (0.2 Msol) white dwarfs. All four stars show peak-to-peak radial velocity variations of 540 - 710 km/s with 1.0 - 5.9 hr periods. The optical photometry rules out…

We estimate the merger rate of double degenerate binaries containing extremely low mass (ELM) <0.3 Msun white dwarfs in the Galaxy. Such white dwarfs are detectable for timescales of 0.1 Gyr -- 1 Gyr in the ELM Survey; the binaries they…

The theory of binary evolution predicts that many massive stars should lose their hydrogen-rich envelopes via interaction with a companion -- revealing hot helium stars with masses of $\sim$2--8M$_{\odot}$. However, only one candidate…

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs)…

Binaries with a Wolf-Rayet star and a compact object (WR-COs), either a black hole (BH) or a neutron star (NS), have been proposed as possible progenitors for the binary compact object mergers (BCOs) observed with the gravitational wave…

Atmospheric carbon has been detected in the optical spectra of six hydrogen-rich ultra-massive white dwarfs, revealing large carbon abundances (log C/H > $-$0.5) attributable to the convective dredge-up of internal carbon into thin hydrogen…

We have presented 309 new white-dwarf (WD) + main-sequence (MS) star binaries identified from the Sloan Digital Sky Survey (SDSS) Tenth Data Release (DR10). The majority of them consist of a white dwarf and a low-mass secondary (typically M…

Close binary systems are the progenitors to both Type Ia supernovae and the compact object mergers that can be detected via gravitational waves. To achieve a binary with a small radial separation, it is believed that the system likely…

HD 144941 is an extreme He (EHe) star, a rare class of subdwarf OB star formed from the merger of two white dwarf (WD) stars. Uniquely amongst EHe stars, its light curve has been reported to be modulated entirely by rotation, suggesting the…

Recently, a class of Roche-lobe-filling binary systems consisting of hot subdwarf stars and white dwarfs with sub-hour periods has been discovered. At present, the hot subdwarf is in a shell He burning phase and is transferring some of its…

Extremely-low-mass white dwarfs (ELM WDs) with non-degenerate companions are believed to originate from solar-type main-sequence binaries undergoing stable Roche lobe overflow mass transfer when the ELM WD progenitor is at (or just past)…