Thermal Balance Calculation

When the condition of thermal equlibrium is imposed, then the temperature is determined as a function of ionization parameter for a photoionized plasma. Figure 8 shows the ionization and temperature of an optically thin low density photoionized gas with a $\varepsilon^{-1}$ ionizing continuum, as a function of ionization parameter. This can be compared with the results of KM82, model 7 (although that model was not optically thin for log($\xi $)$\leq$2). The current model is significantly more highly ionized; the ionization parameter where the abundances of O VII and VIII reach their maximum is lower by 0.5 dex in the current models. The temperature calculated here is lower; this may be due to a different choice of low and high energy spectral cutoffs which affect the Compton equilibrium temperature.