Related papers: Benchmark ultra-cool dwarfs in widely separated bi…
We present Chandra and Swift X-ray observations of four extremely low-mass (ELM) white dwarfs with massive companions. We place stringent limits on X-ray emission from all four systems, indicating that neutron star companions are extremely…
We identify SDSS J130033.48+590407.0 as a common proper motion companion to the well-studied DA white dwarf PG 1258+593 (GD322). The system lies at a distance of 68 +/- 3 pc, where the angular separation of 16.1 +/- 0.1 arcsec corresponds…
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…
The Sloan Digital Sky Survey turned out to be very efficient in identifying white dwarf/main sequence binaries (WDMS). The population of WDMS systems consists of wide systems whose stellar components evolve like single stars and - more…
Using high-contrast imaging with the SPHERE instrument at the VLT, we report the first images of a cold brown dwarf companion to the exoplanet host star HD4113A. The brown dwarf HD4113C is part of a complex dynamical system consisting of a…
We present the results of a high-resolution spectral differential imaging survey of 12 nearby, relatively young field L dwarfs (<1 Gyr) carried out with HST/NICMOS to search for planetary mass companions at small physical separations from…
White dwarfs carry information on the structure and evolution of the Galaxy, especially through their luminosity function and initial-to-final mass relation. Very cool white dwarfs provide insight into the early ages of each population.…
Although white dwarfs are believed to be the end point of most stellar evolution, unlike main sequence stars, they have not yet been the subject of dedicated time-domain surveys for exoplanets. We discuss how their size and distinctive…
With a spectral type of T10, UGPS J072227.51-054031.2 is one of the coolest objects known to date in the solar neighborhood. Multiple systems are relatively common among early and mid-T dwarfs. We search for faint and close companions…
The discovery and subsequent detailed study of T dwarfs has provided many surprises and pushed the physics and modeling of cool atmospheres in unpredicted directions. Distance is a critical parameter for studies of these objects to…
Ultra-cool dwarfs have been defined as dwarfs with spectral types of M7 or later (Kirkpatrick, Henry, & Irwin 1997) and thus include the new L and T spectral classes. The previous IAU report on ultra-cool dwarfs in 1999 described the…
About a third of the hot subdwarfs of spectral type B, which are mostly core-helium burning objects on the extreme horizontal branch, are found in close binaries with cool, low-mass stellar, substellar, or white dwarf companions. They can…
We present FUSE H Lyman series spectroscopy of the hot white dwarf companion to the 4th magnitude A1III star Beta Crateris, which shows that is has an unusually low mass, 0.43Msun, and has almost certainly evolved through binary…
Virtually all binaries consisting of a white dwarf with a non-degenerate companion can be classified as either close post-interaction systems (with orbital periods of a few days or less), or wide systems (with periods longer than decades),…
The system WDS 16329+0315 is an old, nearby quintuple physical system in the thick Galactic disc formed by a close-resolved, triple primary of solar metallicity, namely HD 149162, and a very wide, common proper motion, secondary pair,…
The ROSAT WFC survey has provided us with evidence for the existence of a previously unidentified sample of hot white dwarfs (WD) in non-interacting binary systems, through the detection of EUV and soft X-ray emission. These stars are…
A near-infrared excess is detected at the white dwarf PHL5038 in UKIDSS photometry, consistent with the presence of a cool, substellar companion. We have obtained H- and K-grism spectra and images of PHL5038 using NIRI on Gemini North. The…
We study ultralight scalar fields with quadratic couplings to Standard-Model fermions and derive strong constraints from white-dwarf mass-radius data. Such couplings source scalar profiles inside compact stars, shift fermion masses, and can…
Ultra-cool brown dwarfs offer a unique window into understanding substellar atmospheric physics and chemistry. Their strong molecular absorption bands at infrared wavelengths, Jupiter-like radii, cool temperatures, and lack of complicating…
We present a near-infrared spectrum of the hot ($T_{\rm eff}$ $\approx$ 55,000 K) DA white dwarf PG 1234+482. We confirm that a very low mass companion is responsible for the previously recognised infrared photometric excess. We compare…