Classical Novae and Their Contribution to Galactic Chemical Evolution

James Edward Lyke

Under the supervision of Dr. Robert D. Gehrz and Dr. Charles E. Woodward

ABSTRACT

I examine the role of classical novae in the chemical evolution of the Galaxy. Classical novae are the result of a thermonuclear runaway (TNR) of H–rich material on the surface of a white dwarf (WD) in a close binary system. Each outburst ejects ~10-4 M of enriched chemical material into the interstellar medium (ISM). The ejecta contain both material synthesized in the TNR and previously processed material dredged–up from the WD. The nucleosynthesis of classical novae can account for a majority of the 13C, 15N, and 17O in the Galaxy. Additionally, classical novae can produce locally significant quantities of rare isotopes such as 22Ne and 26Mg that are observed with high abundances in meteorite inclusions.

A target of opportunity observing program provided a random sample of six classical novae (V2313 Ophiuchi, V1425 Aquilae, V4361 Sagittarii, CP Crucis, V1141 Scorpii, and V4633 Sagittarii) for study. I obtained spectra of this sample of novae in the near– to far–infrared (IR) using the European Space Agency's Infrared Space Observatory (ISO) and in the optical and near–IR using a variety of ground–based observatories. Classical novae emit light over most of the electromagnetic spectrum. Therefore, space–based observations are central to the understanding of the classical novae because they provide unimpeded wavelength coverage that is impossible from the ground and higher sensitivity to follow targets as they dim. My method was to observe each object over a broad wavelength range at several epochs to study the ejecta development. We performed detailed modeling analysis of the spectra of V1425 Aquilae and CP Crucis to determine the mass and chemical abundances of their ejecta. Both novae were found to be highly overabundant with respect to the sun in N and O while CP Crucis had a high abundance of Ne. Additionally, these analyses allowed us to estimate the nuclear fusion turn–off times and infer the type of the underlying WD. I present the calculated distances, the spectra, and the observed emission lines of our sample of classical novae.