Ultraviolet observations of novae

Ultraviolet observations of novae give information about 'hot' regions. Observations in this region are important for determining luminosities and effective temperatures. In addition, strong (including resonance) lines, particularly of highly ionized species, occur in the ultraviolet; their study can give information about either photoionization from a hot continuum or collisional ionization and excitation in a hot region. Moreover the examination of ultraviolet spectral lines can provide estimates of electron densities and temperatures and lead to the determination of element abundances. Studies of novae in the ultraviolet can be divided into three categories: novae in early post-maximum development, in the nebular stage and finally as post-novae. Observations of the first of these three stages given information about the development of continued ejection and the pseudo-photosphere in particular while those of the second stage are related to the physics of the expanding nebula-like ejected envelope. Observations in the last category give results concerning the underlying binary, especially the accretion disk. Observations of each stage and their interpretation will be made and general conclusions drawn. (author)