We have briefly described the evolution and characteristics of massive stars, and described the usefulness of obtaining accurate data amongst the galaxies of the Local Group. Such information allows us to test models of how massive stars evolve at different metallicities. And, we've seen that along the way there are many exciting new discoveries: a large population of LBV-like stars among Local Group galaxies, red supergiants that change their effective temperatures by large amount over the period of months, LBVs and yellow supergiants (admittedly in more distant galaxies) exploding as core-collapse supernovae in front of our very eyes, and more.
Many questions remain. What are the true nature of the LBVs candidates? How do the relative number of evolved massive stars of various kinds (LBVs, YSGs, RSGs) compared to the number of their progenitors? Why are some of the most luminous RSGs found at low metallicity highly variable in their spectral properties? Why do the evolutionary models fail to predict as many WCs as observations show at high metallicity? What is the true binary frequency of massive stars?
Work is continuing on characterizing the massive star populations in order to provide sensitive tests of massive star evolutionary models. At present, the most pressing and achievable goals are (1) to compare the binary frequency of WR stars in M31 and the center of M33 (where the models don't correctly predict the WC/WN ratios) with that in the outer portions of M33 (where the models do predict the right ratios), completing the WR survey for IC 10, characterizing the WR content of IC 10, identifying the nature of the LBV "candidates" (based upon their spectral similarities to known LBVs) in M31 and M33, and better determining the numbers of RSGs in the SMC.
Through such work, we gain not only a better understanding of massive stars, but provide the means for improving stellar evolutionary models. Such models are needed for population synthesis, allowing us to better understand how they contribute to the ecology of more distant star-forming galaxies, and the production of supernovae of various types. Although studies of exoplanets and high-redshift cosmology are often newsworthy, many exciting discoveries are awaiting to be made in stellar astrophysics!
Ongoing collaboration with Maria Drout, Emily Levesque, Georges Meynet and especially Kathryn Neugent is gratefully acknowledged. Peter Conti, Deidre Hunter, Emily Levesque, and Kathryn Neugent all kindly made very useful comments on an early draft of this manuscript. This work was partially supported by the National Science Foundation through AST-1008020.