Beyond the iron group: Heavy metals in hot subdwarfs
Abstract
We report the discovery of strong photospheric resonance lines of Ga III, Ge IV, Sn IV and Pb IV in the UV spectra of more than two dozen sdB and sdOB stars at temperatures ranging from 22 000 K to 40 000 K. Lines of other heavy elements are also detected, however in these cases more atomic data are needed. Based on these discoveries, we present a hypothesis to explain the apparent lack of silicon in sdB stars hotter than ∼32 000 K. The existence of triply ionised Ge, Sn, and Pb suggests that rather than silicon sinking deep into the photosphere, it is removed from the star in a fractionated stellar wind. This hypothesis provides a challenge to diffusion models of sdB stars.
Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #8635 and #5319.- Publication:
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Astronomy and Astrophysics
- Pub Date:
- August 2004
- DOI:
- 10.1051/0004-6361:200400027
- arXiv:
- arXiv:astro-ph/0407067
- Bibcode:
- 2004A&A...423L..25O
- Keywords:
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- stars: subdwarfs;
- stars: abundances;
- Astrophysics
- E-Print:
- 5 pages, 3 figures, to appear in A&