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

TL;DR

This study provides a detailed multi-wavelength analysis of planetary nebula NGC 6905 and its Wolf-Rayet-type central star HD 193949, revealing its high-ionization structure, stellar features, and physical properties.

Contribution

It offers the first detailed spectral and physical characterization of NGC 6905 and its [WR] central star, including stellar atmosphere modeling and nebular photoionization analysis.

Findings

Detection of over 20 WR features in the central star

Homogeneous chemical abundances across nebular regions

Modeling suggests the star's initial mass around 1 solar mass

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 $T_\mathrm{eff}\lesssim150$ 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 $\times10^{-3}$ 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.