Navegação por Autor "Koester, Detlev"
Resultados 21-33 de 33
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SDSS white dwarf mass distribution at low effective temperatures
(2009) [Trabalho completo publicado em evento] -
A study of cool white dwarfs in the Sloan Digital Sky Survey Data Release 12
(2019) [Artigo de periódico]In this work, we study white dwarfs where 30 000K > Teff > 5000K to compare the differences in the cooling of DAs and non-DAs and their formation channels. Our final sample is composed by nearly 13 000 DAs and more than 3 ... -
The McDonald Observatory search for pulsating sdA stars : asteroseismic support for multiple populations
(2018) [Artigo de periódico]Context. The nature of the recently identified “sdA” spectroscopic class of stars is not well understood. The thousands of known sdAs have H-dominated spectra, spectroscopic surface gravity values between main sequence ... -
The sdA problem : III. New extremely low-mass white dwarfs and their precursors from Gaia astrometry
(2019) [Artigo de periódico]The physical nature of the sdA stars – cool hydrogen-rich objects with spectroscopic surface gravities intermediate between main-sequence and canonical-mass white dwarfs – has been elusive since they were found in Sloan ... -
The sdA problem : II. Photometric and spectroscopic follow-up
(2018) [Artigo de periódico]The spectral classification ‘subdwarfA’ (sdA) is given to stars showingH-rich spectra and submain- sequence surface gravities, but effective temperature lower than the zero-age horizontal branch. Their evolutionary origin ... -
The sdA problem : I. Physical properties
(2018) [Artigo de periódico]The so-called sdA stars are defined by having H-rich spectra and surface gravities similar to hot subdwarf stars, but effective temperature below the zero-age horizontal branch. Their evolutionary history is an enigma: ... -
Thirty-five new pulsating DA white dwarf stars
(2004) [Artigo de periódico]We present 35 new pulsating DA (hydrogen atmosphere) white dwarf stars discovered from the Sloan Digital Sky Survey (SDSS) and the Hamburg Quasar Survey (HQS). We have acquired high-speed time series photometry of preselected ... -
Towards a pure ZZ Ceti instability strip
(2007) [Artigo de periódico]Context. We have observed again two stars inside the ZZ Ceti instability strip that were previously classified as not-observed-to-vary (NOV) by Mukadam et al. (2004) and found them to be low-amplitude variables. Some ... -
Two new pulsating low-mass pre-white dwarfs or SX Phoenicis stars?
(2016) [Artigo de periódico]Context. The discovery of pulsations in low-mass stars opens an opportunity to probe their interiors and determine their evolution by employing the tools of asteroseismology. Aims. We aim to analyse high-speed photometry ... -
White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14
(2019) [Artigo de periódico]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 ... -
White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 16
(2021) [Artigo de periódico]White dwarfs are the end state of the evolution of more than 97 per cent of all stars, and therefore carry information on the structure and evolution of the Galaxy through their luminosity function and initial-to-final ... -
White dwarf mass distribution in the SDSS
(2007) [Artigo de periódico]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 Teff and log g determinations for the ... -
White dwarf variability with gPhoton : pulsators
(2018) [Artigo de periódico]We present results from a search for short time-scale white dwarf variability using gPhoton, a time-tagged data base of GALEX photon events and associated software package. We conducted a survey of 320 white dwarf stars ...
