Model Atmospheres for the Central Stars of Planetary Nebulae

Approximately 70 model atmospheres for the central stars of planetary nebulae have been computed under the assumptions of hydrostatic, radiative and local thermodynamic equilibrium and of plane–parallel stratification. These models have effective temperatures and surface gravities in the range $$30 000 ^\circ K \leqslant T_\text{eff} \leqslant 200 000 ^\circ K \,\text{and} \,3.4 \leqslant \,\text{log} \,g \leqslant 7.5.$$ The atmospheres have been taken to consist of hydrogen, helium, oxygen, nitrogen, carbon and neon, and the opacity included contributions from both ground and excited states of each ion. The transfer equation is solved using Feautrier's method and the temperature corrections are calculated by means of the Krook–Avrett procedure. Particular attention is given to the effects of gravity and chemical composition on the surface fluxes. The photon fluxes in the H I , He I and He II continua and the stellar flux at H β have been tabulated for use in the determination of Zanstra temperatures.