Comparison of optical and radio column-density measurements toward omicron and Persei and zeta Ophiuchi

Optical and radio measurements of interstellar column densities toward two stars are compared in order to improve our knowledge of diffuse cloud geometry, excitation conditions, and molecular abundances. Toward omicron Per, radio column density measurements made with 20' beams (H i, CH, OH) agree with optical determinations, but a measurement with a 1' beam (CO) is an order of magnitude greater than the optical value. Mapping of the radio CO line shows that there is a hole in the CO distribution centered on omicron Per. Whether the star is the cause of the hole is briefly discussed. Toward zeta Oph the radio CO measurement and optical results are in reasonably good agreement. The CO toward zeta Oph has the same velocity and line width as the strongest neutral atomic constituents. Since the CO and CH+ velocities and line widths are significantly different, the two molecules are not spatially coincident