Introduction

Unlike core collapse supernovae, we have no observation of the initial moments of a classical nova outburst. But, as described elsewhere in this volume, we can reconstruct – at least in a broad sense – the explosive and mixing phenomena because of the comparative simplicity of the ejection process. The thermonuclear runaway is the foundation of our understanding. Yet many details of the dynamics remain to be explored and some of the signposts for change are observational since at the moment of ejection, the nucleosynthetic products are contained in – and expelled with – the ejecta. They provide an interpretable record of the stages of the explosion that are otherwise inaccessible to direct observation. The ambiguities of this record, understood only through modeling, will be the subject of our discussion in this chapter.

Decoding the abundance patterns in various subclasses of novae and individual objects has proven a great challenge over the decades since the first edition of this book appeared. Considerable progress has been made in obtaining consistent pictures from a variety of analyses, as we will discuss. Here we will highlight a few of these methods, examine their various limitations and systematic uncertainties, and indicate some directions that new methods of spectroscopic analysis and theoretical modeling can take to improve the picture in the near and long term.