Conditions for Carbon Monoxide Vibration-Rotation LTE in Late Stars

Abstract

Collisional vibration and rotation transition rates are found for carbon monoxide due to H, H2, He and electrons. These rates are compared to the radiative rates of transition in carbon monoxide to establish temperature -pressure regions in which Vibration -Rotation LTE is a good approximation and those regions in which possible non -LTE effects may occur. Comparison of these data with current late star model atmospheres indicates that possible vibrational non -LTE effects may occur in supergiants, but in all late star computed atmospheres rotational LTE should be a good approximation. The further question of total molecular LTE is examined and rate equations set up. Rough order of magnitude estimates are made on the conditions for total LTE in CO.