On the Launching of Optically Thick Outflows from Massive Stars

For decades, massive stars have been seen to lose mass at every stage of evolution. In recent years, detections of outbursts and circumstellar relics uncover transient modes emerging moments before the supernova. The goal of this thesis is to bring theoretical attention into how massive stars launch outflows. In this thesis, we study two modes of mass loss seen during rare, but critical, phases of stellar evolution. The first considers dense, steady outflows from Wolf-Rayet stars. The second considers the eruptions and explosions seen from luminous blue variables (LBVs) and Type IIn supernova (SN) progenitors. Outflows from both systems are optically thick but either radiative or adiabatic in nature. Wolf-Rayet winds are driven by strong radiative pressure on metal lines. Suppressing the outflow is shown to drastically alter the stellar structure with peculiar features including an extended radiative cavity encased in a massive shell. We construct outflow models and conclude the galactic WR population does not harbour such structures. We derive a minimum mass loss rate to launch a transonic, optically thick outflow and find the iron opacity bump to be responsible for launching WR winds. LBVs and Type IIn SN progenitors are seen to abruptly expel mass. Observational inferences suggest the rates are both exceptional and unsustainable with durations exceeding the outer envelope dynamical time. Yet, these outflows are occasionally preceded by fast motions indicative of shock acceleration. In this thesis, we explain how waves can be responsible for these dynamics. We derive an analytic solution wave steepening and shock formation for an inhomogeneous medium. The results suggest that any super-Eddington phenomenon driven by waves \textit{must} involve shocks. Shocks form deep in the star where they are initially weak. We show how weak shocks are capable of accelerating to become strong, breakout, and produce fast ejecta using a revived semi-analytical approximation. We discuss how a train of shocks can heat a large volume of the envelope and eject significant mass.Ph.D