Abstract

Trans-iron element abundances in the hot DO RE0503-289 and the prospective search for technetium

Klaus Werner (Universität Tübingen)

T. Rauch (U. Tübingen, Germany), J.R. Crespo Lopez-Urrutia (MPI for Nuclear Physics, Heidelberg, Germany), J.W. Kruk (NASA GSFC, USA), S. Kucas (U. Vilnius, Lithuania), P. Quinet (U. Mons, Belgium)

The hot DO white dwarf RE0503-289 is unique with respect to its ultraviolet spectrum that exhibits spectral lines of an unusually rich diversity of a dozen of elements beyond the iron group (Zn - Ba, i.e., atomic numbers A = 30 - 56). Abundance analyses are hampered by the scarcity or complete absence of atomic data (energy levels, oscillator strengths) for high ionization stages. We report on our recent efforts to overcome this obstacle. In all hitherto examined cases, the determined element abundances are extremely oversolar. These high abundances could be the result of a past late helium-shell flash, being amplified by radiative levitation. The detection of technetium, the lightest element with solely unstable isotopes, would be interesting to clarify the origin of the extreme heavy-element abundances. We will discuss the chances to detect Tc, based on first-time computed energy levels and oscillators strengths for the relevant ionization stages Tc IV-VI. Despite good prospects, the positive detection of Tc lines is inhibited by the lack of precise wavelength positions that can only be derived with laboratory experiments currently being prepared. These will use an electron beam ion trap operating at low energies in order to generate the required ions in well-defined charge states.

Mode of presentation: oral