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Preprint 01/99

Classification and spectral analysis of faint central stars of highly excited planetary nebulae

T. Rauch (1), J. Köppen (2), R. Napiwotzki (3), and K. Werner (1)

(1) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2) URA1280, Observatoire Astronomique, 11, rue de l'université, F­67000 Strasbourg, France
(3) Dr. Remeis­Sternwarte, Universität Erlangen­Nürnberg, D­96049 Bamberg, Germany

To appear in: Astronomy and Astrophysics

Abstract. We present narrow­band images of nine planetary nebulae (PN) and a spectral analysis of four of their central stars (CSPN) by means of model atmosphere techniques based on medium­resolution optical spectra.
Four of our CSPN are unambiguously identified. They are very hot (T_eff > 100 K) and have about 1 ­ 2 times solar He/H abundance ratios (the exciting stars of PN G214.9+07.8, PN G231.8+04.1, PN G283.6+25.3, PN G293.6+10.9).
Three other of our PN are candidates for Abell 35­like objects: The supposed central stars of PN G257.5+00.6 and PN G277.1 exhibit F­type spectra while probably the hotter exciting star escapes detection in the optical. Absorption features is the spectrum of the central star of G283.6+25.3 suggest the presence of a cool companion.
The images of G277.1-03.8 display two close stars at its center which both show F-type spectra. It appears likely that this is a binary system but better spectra and additional UV spectra are required in order to successfully identify the excit­ ing central star.

Key words: stars: abundances - stars: AGB and post­AGB - stars: atmospheres - stars: evolution - planetary nebulae: general

Paper (2182k gzip'ed Postscript including figures)

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