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 (Teff > 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.