Abstract
Hydromagnetic shock waves in the 10 to 200 km -1 range including the effect of a magnetic field in the 0 to 1 x 10^-4 gauss range perpendicular to the flow, have been computed. Our results for v0 ≤ 16 km s-1 are in very good agreement with those of Field et al. (1968). It is found that in the case of there being no magnetic field and for v0 in the 30 to 60 km -1 range a large fraction of the hydrogen atoms is ionized while most of the helium atoms remain neutral. In the presence of a magnetic field the range in which shydrogen is ionized while helium remains neutral, is shifted to higher velocities. The relevance of our results to some astronomical problems is briefly discussed. In particular the lack of ionized helium in three H II regions near the nucleus of our galaxy can be easily explained if the ionization is due to hydromagnetic shock waves.
