Using the Hdef Grid of High Resolution Synthetic Spectra in the Analysis of Three [WCE] Stars

Low and intermediate mass stars evolve from the Asymptotic Giant Branch (AGB) at an almost constant luminosity towards 
higher temperatures. These stars will, eventually, be hot enough to ionize the surrounding material, which was previously lost 
by the AGB precursor, and become central stars of planetary nebulae (CSPNe). They are very hot objects, have high surface 
gravities and many of them present dense winds, whose features dominate the observed spectra. These winds are likely 
driven by radiation pressure on spectral lines and, thus, unstable and inhomogeneous. We used the Hdef grid of synthetic 
spectra covering the parameter regime of [WC]-type CSPNe (Keller et al. 2011) to analyze UV and far-UV spectra of the hot 
[WCE] central stars of NGC 6905, NGC 5189 and Sand 3. The models are calculated with the non-LTE stellar atmosphere 
code CMFGEN, which accounts for spherically symmetric stationary expanding atmospheres, line blanketing and wind 
clumping and include many ionic species previously neglected. The use of the grid enables a systematic analysis of the 
observed spectra in order to constrain stellar parameters. It also facilitates line identification, and illustrates spectral line 
changes across the CSPN evolutionary phase. The grid is available at http://dolomiti.pha.jhu.edu/planetarynebulae.html. We 
extended the analysis by exploring additional parameters not considered in the main grid, such as the iron abundance, and 
included less abundant ions in the model calculations.