Magnetohydrodynamic shocks in diffuse clouds. III. The line of sight toward Zeta Ophiuchi

Multifluid C-type shock models are presented for the gas on the line of sight toward Zeta Oph and compared with observational data. A shock model of a 9 km/s-shock propagating into diffuse molecular gas with n(H) of 20/cm, and H2/H of 3 is in good agreement with the observed column density and radial velocity of the CH(+) and is consistent with observational limits of column densities of the OH and CH. The preferred shock model predicts that a large fraction of the J = 3-5 H2 on this line of sight is due to collisional excitation in the shock-heated gas. The dominant molecular component present on this line of sight is interpreted as shock-compressed material behind the shock front. It is considered to be likely that the shock wave is driven by the pressure of the Zeta Oph H II region. 53 references