2013MNRAS.436.1152C

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-H2 conversion factor (XCO) varies throughout the cloud. Calibrating XCO with CH data at similar resolution (1arcmin for CO, 1.5arcmin for CH) yields values of XCO ranging from 0.6x10²⁰ to 3.3x10²⁰/cm2 (K.km/s)-1 with an average of 1.3x10²⁰/cm2 (K.km/s)-1. Given that the cloud has a peak reddening of 0.24mag, it should be classed as a diffuse rather than a translucent molecular cloud. The mass obtained from the CO data and our values of XCO is 9.6M_☉ for the core, 12M_☉ for the envelope and 10M_☉ for the periphery of the cloud. A third of the molecular mass of the cloud is found in a region with E(B - V) < 0.12mag. With these mass estimates, we determine that the cloud is not gravitationally bound.