A New Grid of Synthetic Spectra for the Analysis of [WC]-type Central Stars of Planetary Nebulae

TL;DR

This paper introduces a comprehensive grid of synthetic spectra for analyzing hot, hydrogen-deficient post-AGB stars, aiding in parameter determination and spectral interpretation across multiple wavelength regimes.

Contribution

The authors developed a new, extensive grid of synthetic stellar spectra using CMFGEN, covering high temperatures and gravities, including many ionic species previously neglected.

Findings

The grid effectively constrains stellar parameters from UV spectra.

Application to NGC 6905's central star demonstrates its utility.

The full spectral grid is publicly available online.

Abstract

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 (post-AGB) objects hotter than 50000 K, migrating along the constant luminosity branch of the Hertzsprung-Russell diagram (HRD). 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-LTE, 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, i.e., 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 of the stellar spectrum as stars evolve through the central star of planetary nebula (CSPN) phase. We show the effect of major physical parameters on spectral lines in the 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 in 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 far-UV, UV, optical, and IR spectral regions, is available on-line.