Hydrogen densities in molecular clouds inferred from CO observations

摘要: Observations of the J=2-1 and J=1-0 rotational transitions /sup 12/CO, 13/CO, C/sup 18/O are reported for 10 molecular clouds. An analysis data based on a large-velocity-gradient cloud model suggests that in most these sources average hydrogen densities lie between 2000 8000 cm/sup -3/, while 13/CO fractional abundances approximately 3 x 10/sup -6/. These typically factor lower than those inferred from observations other molecules such as HCN, CS, or H/sub 2/CO; possible explanations this discrepancy discussed.