The hunt for ancient novae

Abstract

A nova eruption in a cataclysmic variable (CV) is a thermonuclear explosion on the surface of the white-dwarf primary once it has accreted a critical mass from its late-type companion. Between these eruptions, the binary is supposed to appear as a ’normal’ CV, although for the first tens or hundreds of years, the white dwarf is still heated up which might influence the mass-transfer rate of the binary. To compare the nova-populations with the general CV-one, a large number of old novae are needed. We have conducted a program to recover old novae and study the binary within. We here present the results of this program as well as a new deep wide-field Hα + [NII] survey of cataclysmic variables to search for remnant nova shells around these objects. Such shells have been found around some cataclysmic variables that were hitherto not known as novae. They provide the unambiguous evidence that the system has experienced a nova eruption in the past and thus point to the oldest novae observable.