2020MNRAS.494L..53F

We show that it is not possible to determine the final mass M_fin of a red supergiant (RSG) at the pre-supernova (SN) stage from its luminosity L and effective temperature T_eff alone. Using a grid of stellar models, we demonstrate that for a given value of L and T_eff, an RSG can have a range of M_fin as wide as 3 to 45 M_☉. While the probability distribution within these limits is not flat, any individual determination of M_fin for an RSG will be degenerate. This makes it difficult to determine its evolutionary history and to map M_fin to an initial mass. Single stars produce a narrower range that is difficult to accurately determine without making strong assumptions about mass-loss, convection, and rotation. Binaries would produce a wider range of RSG M_fin. However, the final Helium core mass M_He–core is well determined by the final luminosity and we find log(M_He–core/M_☉) = 0.659 log(L/L_☉) -2.630. Using this relationship, we derive M_He–core for directly imaged SN progenitors and one failed SN candidate. The value of M_fin for stripped star progenitors of SNe IIb is better constrained by L and T_eff due to the dependence of T_eff on the envelope mass M_env for M_env <= 1 M_☉. Given the initial mass function, our results apply to the majority of progenitors of core-collapse SNe, failed SNe, and direct-collapse black holes.