Doctor of Philosophy (PhD)
Physics and Astronomy
We investigated two types of stellar explosions, recurrent novae (RNe) and Type Ia supernovae (SNe Ia). SNe Ia are the most useful distance markers in astrophysics, but we do not know the identity of their progenitor systems. RNe are good progenitor candidates that consist of a white dwarf (WD) that accretes material from a companion star. The material builds on the surface of the WD until a runaway thermonuclear eruption is triggered, which ejects the accreted material and causes the system to brighten dramatically. We studied the demographics of the nova population and concluded that approximately 25% of classical novae are actually RNe for which only one eruption has been discovered. Importantly, this means that there are enough RNe in our galaxy to provide a significant fraction of the SNe Ia. We present a list of good RN candidates; for one such system, V2487 Ophiuchi, we sought and found a previous eruption in the astronomical plate archives.
We examined two known RNe in detail. T Pyxidis has a unique shell; we used observations of the shell and central star to produce a new model for the long-term evolution of the system, which will never become a supernova. U Scorpii erupted in 2010 as predicted. We led a worldwide collaboration of astronomers that discovered the eruption and comprehensively observed it from start to finish. We discovered three new phenomena and were able to make the best-yet measurement of the amount of mass ejected during the eruption.
We searched the centers of nearby SN Ia remnants looking for ex-companion stars left behind after the WD exploded centuries ago. For one remnant, SNR 0509-67.5, we can definitively state that there are no ex-companion stars in the center of the remnant and therefore the system must have consisted of two WDs that collided to form the SN Ia. The other nearby remnants have possible ex-companion stars; more observations are needed to determine which, if any, are the true ex-companions. Some large fraction of the SNe Ia must come from double-WD systems, but there is a possibility that RNe provide a significant fraction as well.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Pagnotta, Ashley Sara, "Recurrent novae and Type Ia supernova progenitors" (2012). LSU Doctoral Dissertations. 1602.
Schaefer, Bradley E.