**About the Special Issue Editor**

**Roberta M. Humphreys** is Professor Emerita at the University of Minnesota. Her research interests are in observational stellar evolution and Galactic structure. She is best known for her research on massive stars in the Milky Way and in nearby resolved galaxies. In 1979, she and Kris Davidson identified an empirical upper luminosity boundary or upper limit in the luminosity vs temperature diagrams, i.e. the Hertzsprung-Russell (HR) Diagram. This empirical boundary, often referred to in the astronomical literature as the Humphreys-Davidson Limit, was not predicted by theory or the stellar structure models and evolutionary tracks. The lack of evolved stars above a certain luminosity implies an upper limit to the masses of stars, that can evolve to become red supergiants thus altering the previously expected evolution of the most massive stars across the HR Diagram. Her later research has been focused on the final stages of massive stars evolution often dominated by high mass loss events as observed in eta Carinae, and the warm and cool hypergiants. She is an Honorary Fellow of the Royal Astronomical Society, a recipient of the Humboldt Senior Scientist Award, and a Fellow of the American Association for the Advancement of Science.
