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| Paper: |
Atmospheric Parameters and Carbon Abundance for Hot DB White Dwarfs |
| Volume: |
493, 19th European Workshop on White Dwarfs |
| Page: |
77 |
| Authors: |
Koester, D.; Provencal, J.; Gänsicke, B. T. |
| Abstract: |
Accurate atmospheric parameters for DB (helium atmosphere) white
dwarfs near 25000 K are difficult to determine, but are needed to help
or confirm the asteroseismic analysis of these objects. Another
important aspect is the new class of white dwarfs – the hot DQ –
whose spectra are dominated by carbon lines. The origin of these stars
is not yet understood, but they may have an evolutionary link with the
hotter DBs as studied here. We use absolutely calibrated
high-resolution UV spectra of five DBs in addition to available
optical spectroscopy. We find photospheric C and no other heavy
elements – with extremely high limits on the C/Si ratio – in two of
the five objects. We compare various explanations for this unusual
composition that have been proposed in the literature: accretion of
interstellar or circumstellar matter, radiative levitation, carbon
dredge-up from the deeper interior below the helium layer, and a
residual stellar wind. None of these explanations is completely
satisfactory, and the problem of the origin of the hot DQ remains an
open question. |
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