The C/CO ratio in dense interstellar clouds

Abstract

The cosmic-ray-induced photodestruction (CRIP) of CO in dense interstellar clouds is investigated by means of numerical simulations to determine the C/CO abundance ratio. The model takes the dependence of C/CO on the rotational temperature, abundance, and velocity distribution of the CO into account. The results are presented in a table and briefly characterized. A uniform 30-K cloud with CO/H2 = 0.00015 is found to have steady-state C/CO = 0.005 when CRIP is included, about 1000 times the ratio without CRIP. The unusually high C/CO of 0.1 seen in some clouds (Keene et al., 1985) is explained in terms of a C depletion factor of 0.001 relative to O and a velocity difference through the cloud of about 10 km/s.