Spherically symmetric, expanding, non-LTE model atmospheres for novae during their early stages

Abstract

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 « 10 4 K, L = 2 x 10 4 L 0 , p out « 3 x 10~1 5 g cm-3 , M ä 10~5 M 0 yr-1 leading to a maximum expansion velocity of v & 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.

Multiwavelength analyses of the extraordinary nova LMC 1991

“…The resulting UV spectral energy distribution is referred to as the pseudo‐continuum because of the severe line blanketing from the overlapping absorption lines. The true continuum is visible only through gaps in this ‘iron curtain’ (Hauschildt et al 1992; Shore et al 1994) which gives the phase its name. The UV energy absorbed is re‐emitted in the optical and infrared; thus visual maximum occurs when the UV absorption is greatest.…”

“…The model atmospheres are characterized by the following parameters (see Hauschildt et al 1992, 1995, 1997 for details):…”

Time-dependent radiative transfer calculations for supernovae

“…3 3 In many papers, it is referred to as the thermalization parameter, and can be thought of as the fraction of line photons that are ‘absorbed’ on a given line interaction (e.g. Hauschildt et al 1992). This probability not only allows for true absorption, but also, for example, re‐emission of a photon from the upper level in another bound–bound transition. …”

Analyses of the LMC Novae

“…Our study includes analysis of both the early, optically thick spectra using model atmospheres (Hauschildt et al 1992), and the later nebular spectra using optimization of photoionization codes (Ferland 1996;James & Roos 1993). By analysing all the LMC novae in a consistent manner, we can compare their individual results and use their combined properties to calibrate Galactic novae.…”

“…We have begun a study of these objects using ultraviolet spectra obtained by IDE and optical spectra from nova surveys. We are using the results of this study to further our understanding of novae and stellar evolution.Our study includes analysis of both the early, optically thick spectra using model atmospheres (Hauschildt et al 1992), and the later nebular spectra using optimization of photoionization codes (Ferland 1996;James & Roos 1993). By analysing all the LMC novae in a consistent manner, we can compare their individual results and use their combined properties to calibrate Galactic novae.…”