AAS 200th meeting, Albuquerque, NM, June 2002
Session 73. Interim Stellar Materials: Gas, Dust and Clouds
Display, Thursday, June 6, 2002, 9:20am-4:00pm, SW Exhibit Hall

## [73.04] E(B-V), CO, and CH as Molecular Gas Tracers in a Translucent Cloud

H.C. Kim (Columbia University), R.J. Chastain (University of Washington), L. Magnani (University of Georgia)

The efficacy of three molecular hydrogen gas tracers - the CO(1-0) transition, the CH 2\ Pi1 \over 2, J={1 \over 2}, F=1-1 transition, and the color excess, E(B-V) - is evaluated for the translucent molecular cloud MBM16. The CH emission line and E(B-V) are well-correlated wi th each other but not with the CO(1-0) emission line. It is likely that in translucent molecular clouds the CO is not a linear tracer of the molecular hydrogen column density because, in these objects, the CO/H2 ratio is undergoing rapid fluctuations as a function of the molecular hydrogen column density. For translucent and diffuse molecular clouds, and possibly for the translucent envelopes of giant molecular clouds, CH observations should be used to calibrate the CO to H2 conversion factor.