SPHERICALLY SYMMETRICAL, EXPANDING, NON-LTE MODEL ATMOSPHERES FOR NOVAE DURING THEIR EARLY STAGES

Continuum and line-blanketed models for the photospheres of novae in the early stages of their outbursts are presented. The spherically symmetric, non-LTE, line blanketed expanding atmospheres are characterized by a very slow decrease of density with increasing radius. This feature leads to very large geometrical extensions so that there are large temperature differences between the inner and outer parts of the line-forming regions. The theoretical spectra show a large IR excess and a small Balmer jump which may be either in absorption or in emission. For the parameters considered (T(eff) almost-equal-to 10(4) K, L = 2 x 10(4) L., rho(out) almost-equal-to 3 x 10(-15) g cm-3, M almost-equal-to 10(-5) M. yr-1 leading to a maximum expansion velocity of upsilon almost-equal-to 2000 km s-1, solar composition), most lines are in absorption. The effects of changes in the abundances of the heavy elements on the emergent spectra are discussed. We find that the strong unidentified features, observed in ultraviolet spectra of novae, are in actuality regions of transparency within the Fe "forest." We display ultraviolet spectra, obtained from the IUE archives, and do spectral synthesis of these spectra using our theoretical atmospheres.