Mike J. Barlow 1, D. Gehrz 2, A. Evans 3, S. Eyres 3, M.A. Greenhouse 4, M.F. Kessler 5, J. Krautter 6, D. Péquignot 7, A. Salama 5, & C. Woodward 8
1 University College London
2 University of Minnesota
3 Keele University
4 National Air and Space Museum, Washington
5 Vilspa
6 Landessternewarte Heidelberg
7 University of Wyoming
A nova eruption originates as a result of a thermonuclear runaway (TNR)
on the surface of a white dwarf in a semi-detached binary system. In the
course of the eruption some
of material is ejected,
at
,
and enriched in metals as a result of the TNR.
Nova eruptions provide an unparalled opportunity to observe a number of poorly-understood astrophysical processes, essentially in real time. These include the common envelope phase, when both stars are engulfed in the ejected material, the formation of dust grains, and the evolution of the nebular and coronal spectrum as the ejected material disperses and the stellar remnant evolves. Forbidden lines cool the ejected shell, and a range of ionization states, up to several hundred eV in ionization potential, are observed simultaneously. Elemental abundances derived from this line emission are believed to trace the chemical composition of the white dwarf core, leading to the conclusion that there are two distinct classes of white dwarf (CO and ONeMg) in nova systems.
The ISO mission has given us a unique opportunity to follow in detail, for the first time, the evolution of nova eruptions in the far infrared. Target-of-opportunity observations of six novae in outburst have been carried out, with the SWS and LWS. These observations have been supplemented by ground-based observations, at optical, near infrared and radio wavelengths. Many of these ground-based observations were carried out within days of the ISO observations, giving quasi-simultaneous wavelength coverage over 10 octaves - another unique feature of this programme.
Observations for nova V723 Cas, which erupted in 1995, are particularly extensive, covering some 600 days. This contribution will review the evolution of novae in eruption as seen by ISO, with particular emphasis on Nova V723 Cas.