Non-LTE model atmospheres for central stars of planetary nebulae

Abstract

A grid of hot non-LTE model atmospheres with H and He opacity sources has been calculated. The emergent fluxes, together with integrals required for Zanstra and Energy-Balance methods, are presented. These are needed for the analyses and modelling of planetary nebulae. The grid spans the following ranges: Teff: 40–180×103K, log g: 4.0–8.0, He/H: 10 and 1 per cent by number. The low helium abundance models are included to study the effects of gravitational settling in some central stars. The grid of models has been chosen so that the models cover adequately, in the temperature–gravity plane, Schönberner's evolutionary tracks for central stars. Some results on the non-LTE populations of He+ levels and the formation of the He II continuum are described. Model fluxes in the He II continuum are found to be sensitive to atmospheric parameters and to adopted He+ collision rates, when Teff<105K. Use of these models to fit stellar continua between the near-ultraviolet and optical regions yield colour temperatures about 15–20 000 K lower than blackbody temperatures. The desirability of analysing planetaries as complete systems, with photospheres, winds and nebulae modelled consistently, is discussed.

Keywords

Affiliated Institutions

• University College London GB

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