DIFFUSE MOLECULAR GAS IN THE POLARIS FLARE

We present 21 cm line observations of two galactic cirrus clouds, the Polaris Flare and LVC 127, and compare the H I emission with that of C O and with emission in the IRAS bands at 100 mu m and 60 mu m. The 100 mu m emission per hydrogen nucleus is constant outside, but lower ins ide the CO emitting volume. We also find an infrared excess emission o ver and above what can be related to HI or CO emission. We conclude th at apart from the diffuse atomic hydrogen and the denser molecular hyd rogen traced by CO emission, there is a third gas component of diffuse molecular hydrogen. In places the diffuse H-2 has a column density ri valling that of H I. In general it does not contain a denser CO emitti ng interior. The fact that the diffuse H-2 is not traced by CO emissio n is due to the lower gas density, either because CO is not collisiona lly excited, or because the H-2 is not effective enough in shielding C O molecules from photodissociation. We find a conversion factor X betw een CO line integral and H-2 column density similar to other values fr om cirrus clouds, but lower than values for galactic plane clouds deri ved from gamma ray studies. If we account for the lower 100 mu m emiss ion per hydrogen in the CO emitting volume, the difference is reduced, and our X may be consistent with the lower values found in a recent g amma ray study.