The effects of FeII non-LTE on nova atmospheres and spectra
- Department of Physics and Astronomy, Arizona State University, Box 871504, Tempe, Arizona 85287-1504 (United States)
- Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks, Room 131, Norman, Oklahoma 73019-0225 (United States)
- Department of Physics, Wichita State University, Wichita, Kansas 67260-0032 (United States)
The atmospheres of novae at early times in their outbursts are very extended, expanding shells with low densities. Models of these atmospheres show that non-LTE effects are very important and must be included in realistic calculations. We have, therefore, been improving our atmospheric studies by increasing the number of ions treated in non-LTE. One of the most important ions is FeII, which has a complex structure and numerous lines in the observable spectrum. In this paper we investigate non-LTE effects for FeII for a wide variety of parameters. We use a detailed FeII model atom with 617 level and 13,675 primary lines, treated using a rate-operator formalism. We show that the radiative transfer equation in nova atmospheres {ital must} be treated with sophisticated numerical methods and that simple approximations, such as the Sobolev method, {ital cannot} be used because of the large number of overlapping lines in the comoving frame. Our results show that the formation of the FeII lines is strongly affected by non-LTE effects. For low effective temperatures, {ital T}{sub eff}{lt}20,000 K, the optical FeII lines are most influenced by non-LTE effects, while for higher {ital T}{sub eff} the UV lines of FeII are very strongly affected by non-LTE. The departure coefficients are such that FeII tends to be overionized in non-LTE when compared to LTE. Therefore, FeII non-LTE must be included with sophisticated radiative transfer in nova atmosphere models in order to analyze observed nova spectra reliably. Finally, we show that the number of wavelength points required for the FeII non-LTE model atmosphere calculations can be reduced from 90,000 to about 30,000 without changing the results if we choose a sufficiently dense UV wavelength grid. {copyright} {ital 1996 The American Astronomical Society.}
- OSTI ID:
- 285533
- Journal Information:
- Astrophysical Journal, Vol. 462, Issue 1; Other Information: PBD: May 1996
- Country of Publication:
- United States
- Language:
- English
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