MAssivE STaR Outflows (MAESTRO)

Massive stars are key components of galaxies. Characterized by high luminosities and strong outflows, their evolution is strongly impacted by the amount of mass and angular momentum lost through stellar winds. While previously deemed smooth and spherically symmetric, the outflows of massive stars are now found to be inhomogeneous, i.e. clumpy. This severely hampers earlier estimates of the mass-loss rate of hot massive stars and the validity of mass-loss recipes widely adopted in stellar evolution and population synthesis computations.\nIn the context, the MAESTRO (MAssivE StaR Outflows) project aims to achieve a comprehensive analysis of the wind structure by combining ultraviolet and optical observational diagnostics and a new generation of stellar wind models capable of a detailed treatment of clumping structure (including porosity and vorosity).\n \nTo derive meaningful results and improve on existing mass-loss recipes, we need to study\nof a representative set of massive stars covering the upper Hertzsprung-Russell diagram (HRD) and in multiple metallicity environments (as required to investigate the cosmologically important metallicity dependence of the mass-loss rates).\n \nUnfortunately, existing FUV archival data do not offer sufficient coverage of the HRD at sub-solar metallicity. We therefore propose to use COS/G140L to obtain FUV spectroscopy of 42 massive stars that have been selected to fill existing gaps in the parameter space. This will provide us with a continuous view of the mass-loss and clumping properties as a function of stellar mass and of metallicity, allowing us to derive modern prescriptions for the ouflows of massive stars.