2014MNRAS.438.2267H

We model the post-shock accretion column (PSAC) of intermediate polars with the specific accretion rate being floated in the range between 0.0001 and 100 g/cm2/s and the metal abundance in the range between 0.1 and 2 times of the solar, and taking into account the gravitational potential with radial dependence, non-equipartition between ions and electrons and ionization non-equilibrium. We fully take into account the dipole geometry for the PSAC. The specific accretion rate significantly affects the structure of the PSAC, and there is a critical rate below which the profiles of the density and temperature distributions deviate from those of the Cropper model. This happens when the specific accretion rate is 5 and 100 g/cm2/s for the 0.7 and 1.2M_☉ white dwarf (WD), respectively, or the height of the PSAC becomes 1 percent of the WD radius. Below the critical specific accretion rate, the Cropper model is no longer valid. We calculate the spectra of the PSACs with the density and temperature distributions described above. Input parameters are the mass of the WD, the specific accretion rate and the metal abundance. The spectral shape is constant and consistent with that of the Cropper model if the specific accretion rate is larger than the critical value, except for density-dependent emission lines. Below the critical specific accretion rate, on the other hand, the spectra soften as the specific accretion rate decreases. Associated with this, the maximum temperature of the PSAC becomes significantly lower than that of the Cropper model below the critical specific accretion rate. Although the ionization non-equilibrium are also considered in the spectral calculation, the effects are limited because the radiation from ionization non-equilibrium plasma is a few percent of the whole at most.