A high-resolution study of the CO-H^sub 2^ conversion factor in the diffuse cloud MBM 40

We made CO(1-0) observations of 103 lines of sight in the core and envelope of the high-latitude cloud MBM 40 to determine how the CO-H^sub 2^conversion factor (X^sub CO^) varies throughout the cloud. Calibrating X^sub CO^ with CH data at similar resolution (1 arcmin for CO, 1.5 arcmin for CH) yields values of X^sub CO^ ranging from 0.6 x 10^sup 20^ to 3.3 x 10^sup 20^ cm^sup -2^ (K km s^sup -1^)^sup -1^with an average of 1.3 x 10^sup 20^ cm^sup -2^ (K km s^sup -1^)^sup -1^. Given that the cloud has a peak reddening of 0.24 mag, it should be classed as a diffuse rather than a translucent molecular cloud. The mass obtained from the CO data and our values of X^sub CO^ is 9.6 M... for the core, 12 M... for the envelope and 10 M... for the periphery of the cloud. A third of the molecular mass of the cloud is found in a region with E(B - V) < 0.12 mag. With these mass estimates, we determine that the cloud is not gravitationally bound. (ProQuest: ... denotes formulae/symbols omitted.)