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

We present narrow-band 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 medium-resolution optical spectra. Four of our CSPN are unambiguously identified. They are very hot (T_eff, >100 kK) 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 35-like objects: The supposed central stars of PN G257.5+00.6 and PN G277.1-03.8 exhibit F-type spectra while probably the hotter exciting star escapes detection in the optical. Absorption features is the spectrum of the central star of PN G283.6+25.3 suggest the presence of a cool companion. The images of PN 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 exciting central star. Based on observations collected at the European Southern Observatory, La Silla, Chile (proposals 56.D-0717, 57.D-0148)