D. Koester

Publications442
h-index59
Citations10,816
Highly Influential Citations1,098
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Atmospheric parameters of field subdwarf B stars
High signal-to-noise ratio optical spectrophotometry of a sample of field subluminous B stars drawn largely from the Palomar Green ultraviolet-excess survey is analyzed with a new grid of model…
White dwarf mass distribution in the SDSS
We determined masses for the 7167 DA and 507 DB white dwarf stars classified as single and non-magnetic in Data Release 4 of the Sloan Digital Sky Survey (SDSS). We obtained revised T eff and log g…
SDSS DR7 WHITE DWARF CATALOG
We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. We find 20,407 white dwarf spectra,…
Accretion and diffusion in white dwarfs - New diffusion timescales and applications to GD 362 and G 29-38
Context. A number of cool white dwarfs with metal traces, of spectral types DAZ, DBZ, and DZ have been found to exhibit infrared excess radiation due to circumstellar dust. The origin of this dust is…
Metal Lines in DA White Dwarfs
We report Keck telescope HIRES echelle observations of DA white dwarfs in a continuation of an extensive search for metals. These spectra are supplemented with new JHK magnitudes that are used to…
A radio-pulsing white dwarf binary star
TLDR
The discovery is reported of a white dwarf/cool star binary that emits from X-ray to radio wavelengths and the spin-down power is an order of magnitude larger than that seen in electromagnetic radiation, which suggests that AR Sco is primarily spin-powered.
High-resolution UVES/VLT spectra of white dwarfs observed for the ESO SN Ia Progenitor Survey - III. DA white dwarfs
Context. The ESO Supernova Ia Progenitor Survey (SPY) took high-resolution spectra of more than 1000 white dwarfs and pre-white dwarfs. About two thirds of the stars observed are hydrogen-dominated…
The Temperature Scale and Mass Distribution of Hot DA White Dwarfs
Results are presented from a comprehensive spectroscopic survey of DA white dwarfs hotter than ~25,000 K. The observations consisted of CCD spectra with signal-to-noise ratios of ~100 in the blue,…
The accretion-diffusion scenario for metals in cool white dwarfs
We calculated diffusion timescales for Ca, Mg, Fe in hydrogen atmosphere white dwarfs with temperatures between 5000 and 25 000 K. With these timescales we determined accretion rates for a sample of…
New white dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 12
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…
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