The structure of radiative shock waves II . The multilevel hydrogen atom

Models of steady–state plane–parallel shock waves propagating through the unperturbed hydrogen gas of temperature T1 = 6000K and density ρ1 = 10−10 gm cm−3 are computed for upstream velocities 15 km s−1 ≤ U1 ≤ 70 km s−1. The properties of the ambient gas are typical for atmospheres of pulsating stars. The shock wave structure is considered in terms of the self–consistent solution of the radiation transfer, fluid dynamics and rate equations for 2 ≤ L ≤ 4 atomic bound levels with a continuum. The radiative flux FR emergent from the shock wave was found to be independent of the lower limit νL of the frequency range provided that νL < ν2, where ν2 is the Balmer continuum head frequency. At the same time the decrease of νL is accompanied by decrease of the Lyman continuum flux and leads to smaller heating and weaker ionization of the hydrogen gas in the radiative precursor. For all models the size of the radiative precursor is of ∼ 104 cm and corresponds to several mean free paths of photons at the frequency of the Lyman continuum edge ν1. The compression ratio at the discontinuous jump gradually increases with increasing upstream velocity U1, reaches the maximum of ρ+/ρ− = 3.62 at U1 ≈ 55 km s−1 and slowly decreases for larger U1 due to the strong rize of the preshock gas temperature. The radiative flux from the shock wave was determined as a function of the upstream velocity U1 and its ratio to the total energy flux in the shock wave C2 was found to range within 0.18 < FR/C2 < 0.92 for 15 km s−1 ≤ U1 ≤ 65 km s−1. Thus, at upstream velocities U1 > 60 km s−1 the shock wave losses more than 90% of its total energy due to radiation. For all shock wave models the role of collisional processes in both bound–bound and bound– free atomic transitions was found to be negligible in comparison with corresponding radiative processes.