Planetary nebulae with Wolf-Rayet-type central stars - III. A detailed view of NGC 6905 and its central star

We present a multiwavelength characterization of the planetary nebula (PN) NGC 6905 and its [Wolf-Rayet]-type ([WR]) central star (CSPN) HD 193949. Our Nordic Optical Telescope Alhambra Faint Object Spectrograph and Camera (ALFOSC) spectra and images unveil in unprecedented detail the high-ionization structure of NGC 6905. The high-quality spectra of HD 193949 allowed us to detect more than 20 WR features including the characteristic O-bump, blue bump, and red bump, which suggests a spectral type no later than a [WO2]-subtype. Moreover we detect the Ne VII and Ne VIII broad emission lines, rendering HD 193949 yet another CSPN with T_eff ≲ 150 kK exhibiting such stellar emission lines. We studied the physical properties (T_e and n_e) and chemical abundances of different regions within NGC 6905 including its low-ionization clumps; abundances are found to be homogeneous. We used the PoWR stellar atmosphere code to model the spectrum of HD 193949, which is afterwards used in a photoionization model performed with CLOUDY that reproduces the nebular and dust properties for a total mass in the 0.31-0.47 M_⊙ range and a mass of C-rich dust of ~2 × 10^-3 M_⊙. Adopting a current stellar mass of 0.6 M_⊙, our model suggests an initial mass ~1 M_⊙ for HD 193949, consistent with the observations.