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Abstract: During the comparison of synthetic spectra calculated with two NLTE modelatmosphere codes, namely TMAP and TLUSTY, we encounter systematic differencesin the EUV fluxes due to the treatment of level dissolution by pressureionization. Systematic differences may occur due to a code-specific cutofffrequency of the H I Lyman bound-free opacity. This is the case for TMAP andTLUSTY. Both codes predict the same flux level at wavelengths lower than about1500 A for stars with effective temperatures below about 30000K only, if thesame cutoff frequency is chosen.In the case of Sirius B, we demonstrate an uncertainty in modeling the EUVflux reliably in order to challenge theoreticians to improve the theory oflevel dissolution.The theory of level dissolution in high-density plasmas, which is availablefor hydrogen only should be generalized to all species. Especially, the cutofffrequencies for the bound-free opacities should be defined in order to makepredictions of UV fluxes more reliable.



Author: Thomas Rauch Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, T

Source: https://arxiv.org/







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