Effective temperature at a Rosseland optical depth of 2/3 as a function of the transformed mass-loss rate Ṁ_t for our new calculated model sequences. The sequences connected by solid lines all employ D_∞ = 50, while those with dashed and dotted curves indicate sequences using D_∞ = 10 and 4, respectively, as indicated in the plot. For comparison, also various empirical results from the literature are depicted by discrete, gray symbols.