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 are capable of producing 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 manifest 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 collisions. In particular, the most rapidly variable white dwarfs suggest 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 the Gaia mission. I then collect time-series ground-based spectroscopy using the 4.1-m Southern Astrophysical Research (SOAR) Telescope on Cerro Pachón, Chile, to obtain a snapshot of the physics driving the variability. This method uncovers a diverse array of behaviors exhibited by these peculiar stars that comprise the menagerie of “failed” type 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.

Topic: Joshua Reding’s Zoom Meeting

Time: Oct 24, 2022 11:30 AM Eastern Time (US and Canada)

Join Zoom Meeting

https://unc.zoom.us/j/96680036683