Predictions for ¹²C/¹³C and ¹⁶O/¹⁷O surface isotopic ratios in the red supergiant phase. Single-star models and mass gainer models in different luminosity ranges are colored differently. For single-star models, lines mark the limits for models with different initial rotational velocities of 0, 100, 200, 300, 400 km s⁻¹ from right to left. The initial values of ¹²C/¹³C and ¹⁶O/¹⁷O are 90 and 2750.