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Astron. Astrophys. 324, 991-997

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Stellar evolution of low and intermediate-mass stars

III. An application of evolutionary post-AGB models:
the variable central star FG Sagittae

T. Blöcker1,2 and D. Schönberner2

1Institut für Astronomie und Astrophysik, Universität Kiel, D-24098 Kiel, Germany (bloecker@astrophysik.uni-kiel.de)
2Astrophysikalisches Institut Potsdam, Telegrafenberg A27, D-14773 Potsdam, Germany (deschoenberner@aip.de)

Received 7 January 1997 / Accepted 27 February 1997


Based on a set of evolutionary calculations for thermally pulsating post-AGB models we introduce a robust method to measure FG Sge's mass which was found to be FORMULA . The corresponding evolutionary timescale is consistent with the expansion age of the planetary nebula. Assuming that FG Sge's surface was already enriched with heavy elements on the AGB we propose that during the central-star evolution these elements were removed from the superficial radiative layers due to, e.g., dust/gas separation, leaving the deeper convective layers unchanged. During the flash the outward moving envelope convection mixed the stored heavy elements back to the surface.

Key words: stars: evolution - stars: AGB, post-AGB - stars: abundances - stars: individual: FG Sge

Send offprint requests to: T. Blöcker

© European Southern Observatory (ESO) 1997