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Astron. Astrophys. 354, 983-986 (2000)

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2. Structure of the post-shock gas

Apparao (1997) has considered the post-shock structure in the case of Cyg X-3 using the work of Hollenbach and Mckee (1979). He finds the post-shock temperature Ts=4.7[FORMULA]107 K and the temperature structure is given by [FORMULA](x)=b-ax, where x is the distance behind the shock front, [FORMULA] and [FORMULA]. Here T0 is the temperature at a distance x0 and when T0 is small compared to Ts, x0[FORMULA]1.9[FORMULA]109 cm and a=1.7[FORMULA]102 (Apparao 1997). The density structure is given by n(x)=(16/3)n0Ts/T(x), where n(x) is the number density at x and n0 is the pre-shock density at the orbit of the of the black hole and is [FORMULA]7[FORMULA]1012 He cm-3 (the wind of the Wolf-Rayet star is deficient in hydrogen; for simplicity we assume it to contain only helium nuclei and heavier elements in this paper).

Tamm, Fu and Fryxell (1991), while considering accretion of matter on to a compact object passing through the wind of its binary companion find an accretion wake behind the compact object. They find that the shock front is ahead of the compact object at a distance x1[FORMULA]0.1racc. The accretion radius is racc[FORMULA]1.1[FORMULA]1011 cm (Apparao 1997), so that x1[FORMULA]1.1[FORMULA]1010 cm.

The picture given above is considerably altered by the presence of the strong X-ray source and also the X-ray emission from the post-shock gas. The determination of the density and temperature profiles in these conditions is beyond the scope of this work. It may be noted however that the temperature of the post shock gas between the shock front and the compact object can be maintained at a high value by the X-ray irradiation.

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© European Southern Observatory (ESO) 2000

Online publication: February 25, 2000