paper

Massive Multi-species, Multi-level NLTE Model Atmospheres for Novae in Outburst

arXiv:astro-ph/9906238 · doi:10.1086/307895

Abstract

We have used our PHOENIX multi-purpose model atmosphere code to calculate atmospheric models that represent novae in the optically thick wind phases of their outburst. We have improved the treatment of NLTE effects by expanding the number of elements that are included in the calculations from 15 to 19, and the number of ionization stages from 36 to 87. The code can now treat a total of 10713 levels and 102646 lines in NLTE. Aluminum, P, K, and Ni are included for the first time in the NLTE treatment and most elements now have at least the lowest six ionization stages included in the NLTE calculation. We have investigated the effects of expanded NLTE treatment on the chemical concentration of astrophysically significant species in the atmosphere, the equilibrium structure of the atmosphere, and the emergent flux distribution. Although we have found general qualitative agreement with previous, more limited NLTE models, the expanded NLTE treatment leads to significantly different values for the size of many of the NLTE deviations. In particular, for the hottest model presented here (effective temperature of 35000 K), for which NLTE effects are largest, we find that the expanded NLTE treatment reduces the NLTE effects for these important variables: neutral Hydrogen concentration, pressure structure, and emergent far UV flux. Moreover, we find that the addition of new NLTE species may greatly affect the concentration of species that were already treated in NLTE, so that, generally, all species that contribute significantly to the electron reservoir or to the total opacity, or whose line spectrum overlaps or interlocks with that of a species of interest, must be treated in NLTE to insure an accurate result for any particular species.

29 pages, 12 figures

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