TAPIR Seminar

In person: 370 Cahill. To Join via Zoom: 868 5298 8404

ABSTRACT: The effort to infer properties of massive stars from their explosive deaths remains a forefront in stellar astrophysics. In the effort to extract explosion properties from supernova observations we run into a dilemma -- it is the properties of the stellar core which impact the core-collapse mechanism, but it is their Hydrogen-rich envelopes and surrounding material which mediate the observed supernova emission. Motivated in part by the desire to understand those turbulent outer envelopes responsible for early-time supernova emission, we are constructing semi-global 3D radiation-hydrodynamics simulations of cool, luminous stellar envelopes with the Athena++ code in the Red and Yellow supergiant regimes. These simulations reveal extended envelopes with large-scale convective plumes which remain coherent over large fractions of the stellar radius, causing a bulbous, asymmetric surface. During the star's life, this convective structure manifests itself observationally as quasi-stochastic variability over timescales consistent with the convective overturn timescale. In the eventual explosion, the inhomogeneous 3D convective structure smears out the shock breakout, leading to a longer-duration, fainter signal compared to predictions from spherically-symmetric models. This complicates the ability to cleanly infer a stellar radius from shock breakout measurements, but highlights an exciting possibility: that upcoming UV satellite missions such as ULTRASAT and UVEX can provide a new probe into the structure and asymmetry of these inhomogeneous outer stellar layers.