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Abteilung Astronomie

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Preprint 04/96

On the fate of born-again red giants

K. Werner(1,2), S. Dreizler(3), U. Heber(4), and T. Rauch(1,2,3)

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)Lehrstuhl Astrophysik, Universität Potsdam, Germany
(3)Institut für Astronomie und Astrophysik, Universität Kiel, Germany
(4)Dr. Remeis-Sternwarte, Bamberg, Germany

to appear in the proceedings of the 'Stellar Ecology' Workshop, Elba, Italy, June 24-28, 1996

Abstract. Post-AGB stars which are burning hydrogen in a shell and hot white dwarfs may suffer a final helium shell flash. Subsequently the stellar envelope re-expands and the star becomes a 'born-again' red giant. What is the consequence for the chemistry in the envelope? In particular, what surface abundances can be expected and how are they affected by mass loss during the second descent from the AGB? Iben & MacDonald (1995) provided the only appropriate theoretical calculation available up to now for this scenario. We present here the results of spectroscopic analyses from hot H-deficient stars, which we believe to have undergone a late helium flash. The surface abundance pattern strongly varies from star to star. An explanation of this variety demands extensive parameter studies in evolutionary calculations.

Paper (82k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de)
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