The Evolution of Massive Stars as a Function of Metallicity: Closing the Loop in the Local Group

Lowell Observatory, Flagstaff AZ

Investigators

Abstract

This project will characterize the massive star population of the nearby, star-forming galaxies of the Local Group in order to provide critical tests of stellar evolutionary theory. Current models, while successful in some areas, severely overestimate the lifetimes of the most massive yellow supergiants at high metal abundance ("metal" refers to elements above helium in the periodic table). This project will examine massive stars in several Local Group galaxies, where metallicities differ by a factor of 20. A key goal is to measure mass-loss rates to see how the rates depend upon metallicity. Mass loss largely controls the evolution of massive stars, determining whether a star of 40 solar masses (for example) evolves to a yellow supergiant, red supergiant, and/or a Wolf-Rayet star. The data obtained here will permit critical tests and improvement of the latest evolutionary models. Undergraduate students from Northern Arizona University and Wellesley College will have the opportunity to undertake research as part of this project. Finally, spectra obtained in the present proposal will be made available to other researchers, to enable studies of (for example) the interstellar gas in these galaxies.