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Astron. Astrophys. 354, 349-364 (2000)


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The structure of radiative shock waves

II. The multilevel hydrogen atom

Yu.A. Fadeyev 1 and D. Gillet 2

1 Institute for Astronomy of the Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia (fadeyev@inasan.rssi.ru)
2 Observatoire de Haute-Provence - CNRS, 04870 Saint-Michel l'Observatoire, France (gillet@obs-hp.fr)

Received 2 September 1999 / Accepted 16 November 1999

Abstract

Models of steady-state plane-parallel shock waves propagating through the unperturbed hydrogen gas of temperature [FORMULA] and density [FORMULA] are computed for upstream velocities [FORMULA]. 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 [FORMULA] atomic bound levels with a continuum. The radiative flux [FORMULA] emergent from the shock wave was found to be independent of the lower limit [FORMULA] of the frequency range provided that [FORMULA], where [FORMULA] is the Balmer continuum head frequency. At the same time the decrease of [FORMULA] 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 [FORMULA] and corresponds to several mean free paths of photons at the frequency of the Lyman continuum edge [FORMULA]. The compression ratio at the discontinuous jump gradually increases with increasing upstream velocity [FORMULA], reaches the maximum of [FORMULA] at [FORMULA] and slowly decreases for larger [FORMULA] 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 [FORMULA] and its ratio to the total energy flux in the shock wave [FORMULA] was found to range within [FORMULA] for [FORMULA]. Thus, at upstream velocities [FORMULA] 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.

Key words: shock waves – hydrodynamics – radiative transfer


© European Southern Observatory (ESO) 2000

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