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Preprint 06/10

Detection of iron in PG1159 stars

Klaus Werner (1), Thomas Rauch (1), Jeffrey W. Kruk (2)

(1) Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University Tübingen, Sand 1, 72076 Tübingen, Germany
(2) Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA

ApJ 719 (2010), L32

Abstract. Up to now, iron had not been found in any hydrogen-deficient (pre-) white dwarf of spectral type PG1159, despite intense searching in a number of objects. Consequently, an iron deficiency was claimed, in some cases at least 1 dex. The primary indicators were UV lines of Fe VII. Therefore, the search was confined to relatively cool PG1159 stars (Teff < 150,000 K), otherwise Fe is too strongly ionized for a significant population of Fe VII. In this Letter, we announce the discovery of iron in the very hottest PG1159 stars (Teff = 150,000-200,000 K; RX J2117.1+3412, K 116, Longmore 4, NGC 246, H1504+65), based on the identification of the Fe X λλ979.3, 1022.9 lines in spectra obtained with the Far Ultraviolet Spectroscopic Explorer. Surprisingly, our analysis results in a solar iron abundance for these stars. It is conspicuous that they are among the most massive PG1159 stars (0.71-0.82 M sun), in contrast to those objects for which strongest Fe deficiency was claimed (0.53-0.56 M sun).


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