Spectral analyses of late-type WC central stars of planetary nebulae
U. Leuenhagen (1), W.-R. Hamann (2) and C.S. Jeffery (3)
(2) Lehrstuhl Astrophysik der Universität Potsdam, Postfach 601553, D-14415 Potsdam, Germany
(3) Dept. of Physics and Astronomy, University of St Andrews, North Haugh, St. Andrews, Fife KY16 9SS, Scotland
The optical spectra of the seven late-type Wolf-Rayet central stars NGC 40 ([WC8]), BD+30 3639 ([WC9]), He 2-99 ([WC9]), CPD-56 8032, He 2-113, M 4-18 and K 2-16 (all [WC11]) are analyzed by means of spherically expanding model atmospheres. The NLTE simulations account for the elements helium, carbon and oxygen. As main results effective temperature T*, element abundances and final velocity of the wind v_infinity are determined for each star. Assuming distances or luminosities for the objects, also the stellar radii and the mass-loss rates can be fixed. The values of T* and v_infinity are found to be correlated with the spectral subtype ([WC8]: 78 kK, 1000 km/s; [WC9]: 47-49 kK , 700-900 km/s; [WC11]: 30-32 kK, 200-350 km/s). The obtainede carbon-to-helium ratios are about unity (by mass), and the oxygen abundances are between 4 and 10% (mass fractions). Stellar hydrogen abundances are below the limit of save detection in all cases (typically <=2% by mass); however in one star (He 2-113, K 2-16) we find a weak indication for the presence of hydrogen. Furthermore the occurrence of nitrogen lines in two of the stars is discussed qualitatively. The results of these analyses put empirical constraints for the evolutionary status of WC type central stars as post AGB objects and provide input for modeling their planetary nebulae.
In Astron. Astrophys.: 1996, 312, 167
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