UC Berkeley

Type Ia supernovae (SNe) are among the most common astrophysical transients, yet their progenitors are still unknown. Throughout this thesis we examine a specific pathway to these explosions – the double detonation explosion mechanism. In this scenario a white dwarf (WD) is able to explode below the Chandrasekhar mass limit through the aid of an accreted helium shell. An ignition of this helium can send a shock wave into the center of the WD which, upon convergence, can ignite the core causing a thermonuclear runaway resulting in a Type Ia-like explosion.

Prior to this work, the double detonation scenario was not favored as a mechanism for Type Ia SNe, as there was no strong observational evidence supporting it. The first part of this thesis is a calculation of observational predictions of double detonation explosions. We perform hydrodynamical simulations and radiative transport calculations in order to produce testable predictions for observers. In doing so we identify a population of SNe Type Ia that likely arise from the double detonation progenitor channel recognized by the relationship between their Si II velocity and peak luminosity, and characteristic early color evolution.

While the double detonation scenario has mainly been employed to model signatures of SNe Type Ia, requiring WD masses greater than ∼0.9 M⊙ and helium shell masses less than ∼0.01 M⊙, there exists a wide parameter space beyond these limits which allows for more peculiar transients. We examine these regions and relate low mass double detonations to Ca-rich transients by their properties in the nebular phase. We also determine the peculiar signatures of double detonations triggered by thick helium shells. In doing so this work accurately predicts the observable properties associated with these events, which were later seen in SN 2018byg, establishing the most direct evidence to date that there are multiple mechanisms through which WDs explode.