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Abstract
Type Ia supernovae are among the most scientifically valuable objects in modern astronomy, especially as “standard candles” for measuring cosmic distances. Despite their importance, the nature of supernova Ia progenitors remains a mystery—they arise either from a single white dwarf star gradually accreting mass from a companion, or from the merger of two white dwarfs. However, not all white dwarf binary mergers result in a runaway thermonuclear reaction. Should these potential progenitor systems lack the conditions necessary for supernova detonation, they may instead produce a variety of single-star merger products, such as strongly magnetic, massive, fast-rotating, and metal-polluted white dwarfs. These remnants often exhibit unexpected and interesting physics that manifests in their spectral and photometric activity; thus, one best identifies white dwarf merger remnants by investigating the small fraction of white dwarfs that are photometrically variable due to surface activity instigated in interactions. In particular, the most rapidly variable white dwarfs invoke a potential merger origin due to the remnant being spun-up through conservation of angular momentum during the merger process.
To explore this exotic stellar subset, I identify the most rapidly variable white dwarfs observed with the Kepler space telescope, Transiting Exoplanet Survey Satellite (TESS), and Gaia mission. I then collect time-series ground-based spectroscopy using the 4.1-m Southern Astrophysical Research (SOAR) Telescope on Cerro Pach´on, Chile, to obtain snapshots of the physics driving the variability. This method uncovers a diverse array of behaviors exhibited by peculiar stars that comprise the menagerie of “failed” Ia supernovae.
By executing this observation strategy, I established a new class of variable white dwarfs which present rotationally modulated hydrogen Balmer emission with magnetic Zeeman splitting (class DAHe), and which are now a major focus of the worldwide white dwarf community. I also explored the broader relation between white dwarf mass and rotation rate using detailed stellar modeling analysis, and contributed to discoveries of other types of white dwarf merger and partial supernova detonation remnants. These studies offer valuable context for understanding stellar evolution, stellar interactions, and the supernova Ia progenitor question.
