Since the founding of the theory of radiatively-driven stellar winds by Lucy & Solomon (1970) and Castor et al. (1975, hereafter CAK) many of the initial assumptions introduced by these authors were examined. To the most important ones belong the radial streaming approximation (Friend & Abbott 1986; Pauldrach et al. 1986), the wind stability (Abbott 1980; Owocki & Rybicki 1984), the limitations of the Sobolev approach (Poe et al. 1990; Owocki & Puls 1999), the thermal structure of the wind (Drew 1989) and many others.
Another important assumption, studied already at the dawn of the radiatively-driven stellar wind theory by Castor et al. (1976) is the condition of the one-component flow. They discussed encounters which transfer momentum received by absorbing ions (typically C, N, O, etc.) to passive, nonabsorbing ions, mainly hydrogen and helium. They showed that for the high-density winds, such encounters are not important for the overall dynamics of the wind and that high-density winds can be considered as one-component. However, for the low-density winds Springmann & Pauldrach (1992, hereafter SP) showed that momentum transfer between absorbing and nonabsorbing plasma influences the wind thermal balance and even the wind dynamics. Thus, for the low-density winds the flow is essentially multicomponent. They proposed that the so-called "ion-runaway" may occur. Based on the simplified theory of the multicomponent flow many interesting results were seen. Porter & Drew (1995) re-examined the model of a wind-compressed disk in the presence of dynamical decoupling of absorbing ions and passive plasma, Porter & Skouza (1999) showed the possibility of formation of pulsating shells around stars with low-density radiatively driven wind, and Hunger & Groote (1999) explained the H/He abundance anomalies in Bp stars on the basis of helium decoupling.
The first detailed numerical models of multicomponent radiatively driven stellar winds were presented by Babel (1995, 1996). However, Krticka & Kubát (2000, hereafter KK0) showed that due to the functional dependence of the radiative force decoupling does not occur. Moreover, Krticka & Kubát (2001, hereafter KKI) using nonisothermal multicomponent models, concluded that winds of B stars are frictionally heated such that the possibility of decoupling of absorbing ions from the passive plasma is excluded.
The solar wind is well-known to possess large temperature differences between electrons and protons. Such differences were obtained also by Bürgi (1992), who used the three-component models of the solar wind. So the natural question arises, whether similar temperature differences exist in the radiatively-driven stellar wind or, in other words, whether the assumption of equal temperatures of all wind components is acceptable. In this paper we intend to answer this question.
Any effect which deposits heat separately on to individual component of the flow may influence our results. Thus, we shall include the effect of Doppler heating, introduced in the stellar wind domain by Gayley & Owocki (1994, hereafter GO). Because it arises from the dependence of the radiative force on the velocity via the Doppler effect it deposits heat directly to the absorbing ion component and thus, it can trigger the temperature difference between absorbing and passive ions.
Proper treatment of ionization balance may be important for the correct description of decoupling of individual components of the flow. Thus, we decided to compute electrical charges of individual components using adequate ionization balance formulas.
Copyright ESO 2001