Multi-level non-LTE calculations for very optically thick winds and photospheres under extreme NLTE conditions

Details Multi-level non-LTE calculations for very optically thick winds and photospheres under extreme NLTE conditions Multi-level non-LTE calculations for very optically thick winds and photospheres under extreme NLTE conditions

Jun 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988a%26a...199..262p&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 199, no. 1-2, June 1988, p. 262-268.

Statistics

Computation

24

Computational Astrophysics, Optical Thickness, Photosphere, Stellar Winds, Thermodynamic Equilibrium, Continuous Spectra, Iterative Solution, O Stars, Planetary Nebulae, Stellar Envelopes, Ultraviolet Spectra

Scientific paper

A new technique to calculate multilevel non-LTE continuum formation in the UV of stellar winds and plane-parallel, static stellar atmospheres is developed using a local approximate lambda operator similar to those presented by Werner and Husfeld (1985) and Hamann (1986). In the present formulation, the iteration of the transfer equation solution is driven by the relative deviation of the source functions of successive iteration steps, which stabilizes the convergence. At the same time, linear equations for the statistical equilibrium are obtained, which diminishes the computational requirements. The technique has been applied to photospheric and stellar wind models, where convergence is reached even under extreme conditions (very large optical thickness and negligible collisional ionization) for which the usual 'accelerated lambda iteration' fails. Test calculations are presented for radiative driven winds of central stars of planetary nebulae close to the Eddington limit, including extensive model atoms of H, He, C, N, O, Ne, Mg, Si, and S (see Pauldrach, 1987) and for H and He II in the case of plane-parallel static photospheres as described by Herrero (1987).

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