The initial masses of the red supergiant progenitors to Type II supernovae

There are a growing number of nearby supernovae (SNe) for which the progenitor star is detected in archival pre-explosion imaging. From these images it is possible to measure the progenitor's brightness a few years before explosion, and ultimately estimate its initial mass. Previous work has shown that II-P and II-L SNe have red supergiant (RSG) progenitors, and that the range of initial masses for these progenitors seems to be limited to less than or similar to 17M(circle dot). This is in contrast with the cut-off of 25-30M(circle dot) predicted by evolutionary models, a result that is termed the 'red supergiant problem'. Here we investigate one particular source of systematic error present in converting pre-explosion photometry into an initial mass, which of the bolometric correction (BC) used to convert a single-band flux into a bolometric luminosity. We show, using star clusters, that RSGs evolve to later spectral types as they approach SN, which in turn causes the BC to become larger. Failure to account for this results in a systematic underestimate of a star's luminosity, and hence its initial mass. Using our empirically motivated BCs we reappraise the II-P and II-L SNe that have their progenitors detected in pre-explosion imaging. Fitting an initial mass function to these updated masses results in an increased upper mass cut-off of M-hi = 19.0(-1.3)(+2.5)M(circle dot), with a 95 per cent upper confidence limit of <27M(circle dot). Accounting for finite sample size effects and systematic uncertainties in the mass-luminosity relationship raises the cut-off to M-hi = 25 M-circle dot (<33 M-circle dot, 95 per cent confidence). We therefore conclude that there is currently no strong evidence for 'missing' high-mass progenitors to core-collapse SNe.