ORFEUS II echelle spectra: on the influence of iron-group line blanketing in the Far-UV spectral range of hot subdwarfs

We present an analysis of the subdwarf O star Feige 67 with a fully metal-l ine blanketed NLTE model atmosphere based on high-resolution Far-UV (912-20 00 Angstrom) and Near-UV (2000-3400 Angstrom) spectra from new ORFEUS II ec helle observations and the IUE final archive. The Far-UV spectra are heavil y blanketed by iron and nickel lines, preventing the detection of the stell ar continuum and complicating the abundance analysis. Important points concerning the account for blanketing by millions of iron- group lines and for an accurate determination of iron and nickel abundances are discussed: The usage of all theoretically and experimentally known lin e opacities of the iron-group elements, the consideration of a broad wavele ngth range for a reliable determination of the stellar continuum flux, and the role of interstellar reddening. This paper outlines a basic approach fo r spectral analysis of future high-resolution Far-UV spectra of hot compact stars. During this study we re-analyzed the iron and nickel abundance of o ur exemplary object Feige 67 and confirm their extraordinary amount.