K. Werner(1), S. Dreizler(1), U. Heber(2), N. Kappelmann(1), J. Kruk(3), T. Rauch(1), B. Wolff(4)
(1)Institut für Astronomie und Astrophysik, Astronomie, Universität
Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)Remeis-Sternwarte, Bamberg, Universität Erlangen-Nürnberg, Germany
(3)Johns Hopkins University, Baltimore, MD, USA
(4)Institut für Astronomie und Astrophysik, Universität Kiel, Germany
accepted by Reviews in Modern Astronomy
Abstract. Ultraviolet observations performed with space based telescopes during the last few years have improved considerably our understanding of the late stages of stellar evolution of stars with low and intermediate mass. The important role of UV spectroscopy is demonstrated by model atmosphere analyses of hot post-AGB stars and hot white dwarfs. Precise analyses are necessary in order to understand the evolutionary history of these stars and to investigate physical processes in their photospheres.
In particular we address here the hydrogen-deficient post-AGB stars during their hottest phase of evolution (PG 1159 stars). In combination with results from asteroseismology, new insights were obtained concerning the origin of the H-deficiency. In addition we concentrate here on the possible PG 1159 progeny stars, the hot helium-rich white dwarfs (DO stars), and in this context we discuss the mysterious absence of He-rich white dwarfs within a particular interval along the white dwarf cooling sequence (DB gap). Radiative acceleration and gravitational settling of elements determines the composition of the hot WD atmospheres. Despite considerable effort, theoretical modeling of these processes is severely at odds with spectroscopic results.
Paper (630k gzip'ed Postscript including figures)
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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de)
Last updated 04-Aug-1997