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| Paper: |
Search for Metal Pollution in 81 DA White Dwarfs |
| Volume: |
469, 18th European White Dwarf Workshop (EUROWD12) |
| Page: |
445 |
| Authors: |
Koester, D.; Gänsicke, B.; Girven, J.; Farihi, J. |
| Abstract: |
A total of 82 DA white dwarfs have been observed with the Cosmic
Origins Spectrograph on the Hubble Space Telescope in a snapshot
program. The targets were selected to be in the
Teff range from 17 000 – 25 000 K, where optical metal lines
become weak and difficult to detect. Because of the strong Si, C, and
O resonance lines in the UV, this survey has a sensitivity that is
comparable to that of the Keck/VLT searches for CaII K in cooler white
dwarfs. These objects also have no convection zone and thus very short
diffusion timescales, assuring that accretion is currently ongoing.
The spectra have high resolution and in most cases fairly good
S/N. About 60% of them show photospheric metal pollution,
predominantly of Si, but in some cases additional metals are
present. We report the results of a preliminary analysis and discuss
the sources of the accreted matter and the possible rôle of
radiative levitation. |
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