There are a growing number of nearby 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 supernovae (SNe) have Red Supergiant (RSG) progenitors, and that the range of initial masses for these progenitors seems to be limited to ∼ <17M ⊙ . This is in contrast with the cutoff of 25-30M ⊙ predicted by evolutionary models, a result which 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, that 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 cutoff of M hi =19.0 +2.5 −1.3 M ⊙ , with a 95% upper confidence limit of <27M ⊙ . Accounting for finite sample size effects and systematic uncertainties in the mass-luminosity relationship raises the cutoff to M hi =25M ⊙ (<33M ⊙ , 95% confidence). We therefore conclude that there is currently no strong evidence for 'missing' high mass progenitors to core-collapse SNe.

Evolutionary models have shown the substantial effect that strong mass-loss rates ( Ms) can have on the fate of massive stars. Red supergiant (RSG) mass-loss is poorly understood theoretically, and so stellar models rely on purely empirical M-luminosity relations to calculate evolution. Empirical prescriptions usually scale with luminosity and effective temperature, but M should also depend on the current mass and hence the surface gravity of the star, yielding more than one possible M for the same position on the Hertzsprung-Russell diagram. One can solve this degeneracy by measuring M for RSGs that reside in clusters, where age and initial mass (M init ) are known. In this paper we derive M values and luminosities for RSGs in two clusters, NGC 2004 and RSGC1. Using newly derived M init measurements, we combine the results with those of clusters with a range of ages and derive an M init -dependent M-prescription. When comparing this new prescription to the treatment of mass-loss currently implemented in evolutionary models, we find models drastically over-predict the total mass-loss, by up to a factor of 20. Importantly, the most massive RSGs experience the largest downward revision in their mass-loss rates, drastically changing the impact of wind mass-loss on their evolution. Our results suggest that for most initial masses of RSG progenitors, quiescent mass-loss during the RSG phase is not effective at removing a significant fraction of the H-envelope prior to core-collapse, and we discuss the implications of this for stellar evolution and observations of SNe and SN progenitors.

The empirical upper luminosity boundary L max of cool supergiants, often referred to as the Humphreys-Davidson limit, is thought to encode information on the general mass-loss behaviour of massive stars. Further, it delineates the boundary at which single stars will end their lives stripped of their hydrogen-rich envelope, which in turn is a key factor in the relative rates of Type-II to Type-Ibc supernovae from single star channels. In this paper we have revisited the issue of L max by studying the luminosity distributions of cool supergiants (SGs) in the Large and Small Magellanic Clouds (LMC/SMC). We assemble samples of cool SGs in each galaxy which are highly-complete above log L/L =5.0, and determine their spectral energy distributions from the optical to the mid-infrared using modern multi-wavelength survey data. We show that in both cases L max appears to be lower than previously quoted, and is in the region of log L/L =5.5. There is no evidence for L max being higher in the SMC than in the LMC, as would be expected if metallicity-dependent winds were the dominant factor in the stripping of stellar envelopes. We also show that L max aligns with the lowest luminosity of single nitrogen-rich Wolf-Rayet stars, indicating of a change in evolutionary sequence for stars above a critical mass. From population synthesis analysis we show that the Geneva evolutionary models greatly over-predict the numbers of cool SGs in the SMC. We also argue that the trend of earlier average spectral types of cool SGs in lower metallicity environments represents a genuine shift to hotter temperatures. Finally, we use our new bolometric luminosity measurements to provide updated bolometric corrections for cool supergiants.

The mass loss rates of red supergiants (RSGs) govern their evolution towards supernova and dictate the appearance of the resulting explosion. To study how mass-loss rates change with evolution we measure the mass-loss rates (Ṁ) and extinctions of 19 red supergiants in the young massive cluster NGC2100 in the Large Magellanic Cloud. By targeting stars in a coeval cluster we can study the mass-loss rate evolution whilst keeping the variables of mass and metallicity fixed. Mass-loss rates were determined by fitting DUSTY models to mid-IR photometry from WISE and Spitzer/IRAC. We find that theṀ in red supergiants increases as the star evolves, and is well described byṀ prescription of de Jager, used widely in stellar evolution calculations. We find the extinction caused by the warm dust is negligible, meaning the warm circumstellar material of the inner wind cannot explain the higher levels of extinction found in the RSGs compared to other cluster stars. We discuss the implications of this work in terms of supernova progenitors and stellar evolution theory. We argue there is little justification for substantially increasing theṀ during the RSG phase, as has been suggested recently in order to explain the absence of high mass Type IIP supernova progenitors. We also argue that an increase in reddening towards the end of the RSG phase, as observed for the two most evolved cluster stars, may provide a solution to the red supergiant problem.

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By comparing the properties of Red Supergiant (RSG) supernova progenitors to those of field RSGs, it has been claimed that there is an absence of progenitors with luminosities L above log(L/L ⊙ ) > 5.2. This is in tension with the empirical upper luminosity limit of RSGs at log(L/L ⊙ ) = 5.5, a result known as the 'Red Supergiant Problem'. This has been interpreted as evidence for an upper mass threshold for the formation of black-holes. In this paper, we compare the observed luminosities of RSG SN progenitors with the observed RSG L-distribution in the Magellanic Clouds. Our results indicate that the absence of bright SN II-P/L progenitors in the current sample can be explained at least in part by the steepness of the L-distribution and a small sample size, and that the statistical significance of the Red Supergiant Problem is between 1-2σ . Secondly, we model the luminosity distribution of II-P/L progenitors as a simple power-law with an upper and lower cutoff, and find an upper luminosity limit of log(L hi /L ⊙ ) = 5.20 +0.17 −0.11 (68% confidence), though this increases to ∼5.3 if one fixes the power-law slope to be that expected from theoretical arguments. Again, the results point to the significance of the RSG Problem being within ∼ 2σ. Under the assumption that all progenitors are the result of single-star evolution, this corresponds to an upper mass limit for the parent distribution of M hi = 19.2M ⊙ , ±1.3M ⊙ (systematic), +4.5 −2.3 M ⊙ (random) (68% confidence limits).After the initial study by S09, a larger sample of progenitors was used by Smartt (2015, hereafter S15) to revise the value of M max upwards to 17M ⊙ . Further, Davies & Beasor (2018, hereafter DB18) later revisited the complexities of converting a preexplosion brightness to bolometric luminosity L fin , and the conver-

We present an abundance analysis of seven super-star clusters in the disk of M83. The near-infrared spectra of these clusters are dominated by Red Supergiants, and the spectral similarity in the J-band of such stars at uniform metallicity means that the integrated light from the clusters may be analysed using the same tools as those applied to single stars. Using data from VLT/KMOS we estimate metallicities for each cluster in the sample. We find that the abundance gradient in the inner regions of M83 is flat, with a central metallicity of [Z] = 0.21 ± 0.11 relative to a Solar value of Z =0.014, which is in excellent agreement with the results from an analysis of luminous hot stars in the same regions. Compiling this latest study with our other recent work, we construct a mass-metallicity relation for nearby galaxies based entirely on the analysis of RSGs. We find excellent agreement with the other stellar-based technique, that of blue supergiants, as well as with temperature-sensitive ('auroral' or 'direct') H ii-region studies. Of all the H ii-region strong-line calibrations, those which are empirically calibrated to direct-method studies (N2 and O3N2) provide the most consistent results.

The fate of massive stars with initial masses >8M ⊙ depends largely on the mass-loss rate ( M) in the end stages of their lives. Red supergiants (RSGs) are the direct progenitors to Type II-P core collapse supernovae (SN), but there is uncertainty regarding the scale and impact of any mass-loss during this phase. Here we used near and mid-IR photometry and the radiative transfer code DUSTY to determine luminosity and M values for the RSGs in two Galactic clusters (NGC 7419 and χ Per) where the RSGs are all of similar initial mass (M initial ∼16M ⊙ ), allowing us to study how M changes with time along an evolutionary sequence. We find a clear, tight correlation between luminosity and M suggesting the scatter seen in studies of field stars is caused by stars of similar luminosity being of different initial masses. From our results we estimate how much mass a 16M ⊙ star would lose during the RSG phase, finding a star of this mass would lose a total of 0.61 +0.92 −0.31 M ⊙ . This is much less than expected for M prescriptions currently used in evolutionary models.