24 research outputs found
<i>Gaia</i> reveals evidence for merged white dwarfs
We use Gaia Data Release 2 to identify 13,928 white dwarfs within 100 pc of
the Sun. The exquisite astrometry from Gaia reveals for the first time a
bifurcation in the observed white dwarf sequence in both Gaia and the Sloan
Digital Sky Survey (SDSS) passbands. The latter is easily explained by a helium
atmosphere white dwarf fraction of 36%. However, the bifurcation in the Gaia
colour-magnitude diagram depends on both the atmospheric composition and the
mass distribution. We simulate theoretical colour-magnitude diagrams for single
and binary white dwarfs using a population synthesis approach and demonstrate
that there is a significant contribution from relatively massive white dwarfs
that likely formed through mergers. These include white dwarf remnants of
main-sequence (blue stragglers) and post-main sequence mergers. The mass
distribution of the SDSS subsample, including the spectroscopically confirmed
white dwarfs, also shows this massive bump. This is the first direct detection
of such a population in a volume-limited sample.Comment: MNRAS, in pres
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25 years of using the spectroscopic method: where do we stand?
The 21st European Workshop on White Dwarfs was held in Austin, TX from July 23rd to 27th of 2018The spectroscopic technique, which consists in fitting
high signal-to-noise optical spectra with the
predictions of state-of-the-art model atmospheres,
has routinely been used for over 25 years to
measure the atmospheric parameters of DA white
dwarfs, and DB stars as well. We review the technique,
the progress we have made, and more importantly,
we attempt to assess its validity and also
try to identify some of the current challenges in the
physics of white dwarf atmospheres related to the
use of the spectroscopic technique.Astronom