Sticking coefficient for gas accretion onto dust as a function of the gas temperature T for different models: Le Bourlot et al. (2012) in black, Chaabouni et al. (2012) in blue, and Leitch-Devlin & Williams (1985) in red for different dust temperatures T_D = 10,20, 40, 80, 300 K for the dotted, solid, dashed, dot-dashed, and triple dot-dashed red lines respectively. The magenta line at α = 1/3 is our preferred value for unresolved gas densities (see Section 3.4).