A new grid of synthetic spectra for the analysis of [WC]-type central stars of planetary nebulae

We present a comprehensive grid of synthetic stellar-atmosphere spectra, suitable for the analysis of high-resolution spectra of hydrogen-deficient post-asymptotic giant branch objects hotter than 50 000 K, migrating along the constant luminosity branch of the HertzsprungRussell diagram. The grid was calculated with cmfgen, a state-of-the-art stellar atmosphere code that properly treats the stellar winds, accounting for expanding atmospheres in non-local thermodynamic equilibrium, line blanketing, soft X-rays and wind clumping. We include many ionic species that have been previously neglected. Our uniform set of models fills a niche in an important parameter regime, that is, high effective temperatures, high surface gravities and a range of mass-loss values. The grid constitutes a general tool to facilitate determination of the stellar parameters and line identifications and to interpret morphological changes in the stellar spectrum as stars evolve through the central star of planetary nebula phase. We show the effect of major physical parameters on spectral lines in the far-ultraviolet (far-UV), UV and optical regimes. We analyse UV and far-UV spectra of the central star of NGC 6905 using the grid to constrain its physical parameters, and proceed to further explore other parameters not taken into consideration in the grid. This application shows that the grid can be used to constrain the main photospheric and wind parameters, as a first step towards a detailed analysis. The full grid of synthetic spectra, comprising of far-UV, UV, optical and infrared spectral regions, is available online.