The quasi-one-dimensional formulation of the MHD equations is used to describe the ionizing flow in the solar wind's passage through a cometary coma. A set of ordinary differential equations analog to those of Biermann et al., describe the flow along the central stream tube. The nature of the critical (magnetosonic) point is examined for spacial variations R to the minus n power in the ionization rates: the point is a node with shock-free solutions only for locally low gradients, or for interactions with strong cooling. Otherwise, for realistic values n approximately equal to 2, the critical point is a focus and weakly shocked solutions are appropriate. However, in the external field of laboratory simulation experiments, the critical point disappears and the flow is in any case shock-free. (Author)
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