Determination of the temperatures of the central stars of planetary nebulas

The method for determining the ionization temperatures of the central stars of planetary nebulas by means of the intensity ratio of two spectral lines of the C III ion - a forbidden line controlled by collisions and a pseudoresonance line controlled by photoionization - is extended to the ions Si III, Si II, Al II, and Mg I and makes possible determination of the temperatures of the central stars in a wide range from 40,000 degree K to 200,000 degree K. The intensities of the pseudoresonance lines are calculated with allowance for dielectron recombination, which dominates over photorecombination under the conditions of planetary nebulas. The analytic dependences derived for the ratios of the line intensities as functions of the temperatures of the central stars are compared with the analogous dependences obtained as a result of numerical calculations based on photoionization models of nebulas. The method is applied to four nebulas: NGC 3918, NGC 6572, NGC 7009, and NGC 7662. 29 refs., 5 figs., 2 tabs