UC Santa Barbara

The advent of wide-field surveys has led to an exponential increase in the number of supernovae discovered each year. As the sample sizes of these objects have grown, we have discovered supernovae that show greater diversity within their spectroscopic classes than expected, as well as objects that do not fit into traditional classification schemes altogether. Studying these ``extreme" supernovae in greater detail is crucial to understanding the poorly-understood end stages of stars' lives; early-time observations within hours of the supernova explosion probe the progenitor star's stellar structure as well as its circumstellar environment, which can be used to test current theories of stellar evolution.

Here I present studies utilizing photometric and spectroscopic observations, primarily taken by Las Cumbres Observatory, of supernovae that occupy poorly-understood or unpopulated regions of parameter space. First, I examine an object with extreme ejecta velocities. Observations of this Type Ia supernova, SN 2019ein, within days of explosion show some of the fastest-moving ejecta of any supernova. The potential sources of this high-velocity ejecta in the context of the poorly-understood progenitor channels and explosion mechanisms of Type Ia supernovae are explored.

Next, I investigate the powering mechanisms and progenitor systems of supernovae with rapidly-evolving luminosities. High-cadence observations of objects within this region of supernova phase space reveal significant diversity in their circumstellar environments and powering mechanisms. In particular, I show evidence connecting luminous, rapidly-evolving unclassified transients with supernovae powered by interaction with circumstellar material. I also present the first sample study of a new class of supernovae, Type Icn supernovae, with rapidly-evolving light curves powered by interaction with circumstellar material that is both hydrogen- and helium-poor. Studying these unique and rare objects reveals that some are likely the explosions of stars less massive than expected from our current understanding of mass-loss in massive stars. Finally, I present evidence of diversity in the powering mechanisms and progenitors of the well-understood class of Type IIb supernovae. Each of these major findings challenges our understanding of supernova physics as well as theories of mass loss during the final stages of stellar evolution.