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

Abstract

We present a multi-wavelength characterisation of the planetary nebula (PN) NGC 6905 and its [Wolf-Rayet]-type ([WR]) central star (CSPN) HD 193949. Our Nordic Optical Telescope (NOT) 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 $T_{\mathrm{eff}}\lesssim 150$ kK exhibiting such stellar emission lines. We studied the physical properties ($T_{\mathrm{e}}$ and $n_{\mathrm{e}}$) 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${}_{\odot }$ range and a mass of C-rich dust of $\sim$2 $\times 10^{-3}$ M${}_{\odot }$. Adopting a current stellar mass of 0.6 M${}_{\odot }$, our model suggests an initial mass $\sim$1 M${}_{\odot }$ for HD 193949, consistent with the observations.

To appear in MNRAS; 17 pages, 9 figures, 10 tables

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