UC Berkeley

Type Ia supernovae (SNe Ia) are the final brilliant explosion of a carbon-oxygen white dwarf accreting mass from a companion star. At peak brightness, a SN Ia can outshine an entire galaxy of billions of stars. Most SNe Ia have a standardizable luminosity, ideal for use as an extragalactic distance indicator. Measurements of a large sample of SNe Ia over a range of distances enables the estimate of cosmological parameters to help determine the mass-energy content of the Universe (Riess et al. 1998; Perlmutter et al. 1999; Riess et al. 2004; Astier et al. 2006; Riess et al. 2007; Wood-Vasey et al. 2008; Kowalski et al. 2008; Hicken et al. 2009a; Amanullah et al. 2010; Sullivan et al. 2011a; Suzuki et al. 2012).

The cosmological application of SNe Ia is predicated upon relationships between the intrinsic luminosity and light-curve properties. Despite the successful measurement of cosmological parameters using SNe Ia, our understanding of SNe Ia themselves is surprisingly lacking. The SN Ia progenitor system has never been directly observed, making it unclear how many different channels exist to make a SN Ia. The physical nature of the relationship between light-curve parameters and luminosity is also not well understood, and it remains to be seen whether other correlations exist to improve SN Ia distance estimates.

The goal of this dissertation is to shed light on the physics of SNe Ia and search for new correlations to improve distance estimates to SNe Ia by analyzing a large sample of well-observed, high-quality SN Ia light curves. I have collected, reduced, and analyzed optical photometric data for 165 nearby SNe Ia as part of the Lick Observatory Supernova Search (LOSS). These data represent a significant contribution to the existing sample of nearby SN Ia light curves.

After giving a general overview of SNe Ia in Chapter 1, I present the methods used to obtain and reduce the LOSS data in Chapter 2. In Chapter 3, I use the LOSS data in an analysis of the earliest photometry epochs to understand the explosion physics governing the initial rise of the SN Ia light curve. These early data points also provide a means of testing models to constrain the nature of the binary companion star. I do not find evidence for interaction between SN ejecta and a companion star, ruling out theories requiring a red giant as a companion in most cases. In Chapter 4, I combine the data presented in this thesis with other samples in the literature to place constraints on cosmological parameters. I reject a non-accelerating Universe with 99.999% confidence. In Chapter 5, I present a study of an individual peculiar SN Ia that is unlike any previously published object, bucking the relationships normally observed in SNe Ia. Studying extreme SNe Ia may provide insights into understanding the physics of normal SNe Ia.