Single stars (left), mass gainers (middle), and mass donors (right) in the HRD at core carbon depletion, which represents the pre-supernova stage well. The color coding represents the effective temperature at the midpoint of core helium burning (Y_c = 0.5), the remaining hydrogen and helium envelope mass, and the nitrogen-to-carbon ratio, from top to bottom. Data points are stacked such that those with higher log T_eff, M_env, log(N/C) appear above those with lower values. Evolutionary tracks for non-rotating single-star models are also presented with their initial mass indicated. In the mass donor panel on the second row, the data point for SN 1993J progenitor is also shown (Maund et al. 2004).