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Paper: Is the DO-type White Dwarf RE 0503–289 a Unique Object?
Volume: 509, 20th European Workshop on White Dwarfs (EuroWD16)
Page: 189
Authors: Hoyer, D.; Rauch, T.; Werner, K.
Abstract: Trans-iron group elements (atomic numbers Z > 28) are produced by s-process nucleosynthesis on the asymptotic giant branch (AGB). Flash induced mixing during a late thermal pulse (LTP) should strongly enrich their photospheric abundances. While they are so far not found in the hydrogen-deficient post-LTP [WC]-type Wolf-Rayet stars and PG 1159-type stars, they were identified in a small number of DO-type white dwarfs (WDs). Abundance determinations have shown that these are indeed up to about 35000 times solar. The detection of Ge (Z = 32) in some DA-type WDs yields about solar abundances. Thus, an LTP scenario may be a pre-requisite for very high trans-iron group element abundances. Recently, a very high number of lines of trans-iron group elements were discovered in the ultraviolet (UV) spectrum of the DO-type WD RE 0503–289. Abundance analyses by means of non-local thermodynamic equilibrium (NLTE) model-atmosphere techniques have shown that these elements are strongly overabundant (up to about 4 dex) compared to solar values. To prove the suggestion that an LTP is necessary to yield such overabundances, we performed UV spectroscopy with HST/COS of the PG 1159-type star PG 1707+427 and of two DO-type stars, namely PG 0109+111 and WD 0111+002. These three stars are located in the Hertzsprung-Russell diagram close before and after the so-called PG 1159 wind limit. At about this limit, PG 1159-type stars evolve into DO-type WDs. These observations will show whether the high abundances of trans-iron group elements are a common phenomenon and establish constraints for AGB nucleosynthesis and post-LTP evolution. To clarify this, we performed an advanced NLTE spectral analysis and present our preliminary results.
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