Improved NLTE profiles of He II lines in hot stars including their overlap with hydrogen

Details Improved NLTE profiles of He II lines in hot stars including their overlap with hydrogen Improved NLTE profiles of He II lines in hot stars including their overlap with hydrogen

Nov 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987a%26a...186..231h&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 186, no. 1-2, Nov. 1987, p. 231-240. DFG-supported research.

Astronomy and Astrophysics

Astrophysics

17

Gas Ionization, Helium Ions, Hot Stars, Hydrogen, Line Shape, Nonequilibrium Thermodynamics, Early Stars, Spectral Line Width, Stark Effect, Stellar Atmospheres

Scientific paper

The accelerated Lambda iteration method is used to obtain better theoretical profiles of He II in hot stars by considering more levels and Stark broadening in the statistical equilibrium equations. It is found that an appropriate He II model atom must consist of 14 non-LTE levels and that Stark broadening must be included for all lines with upper levels of 7 or less. The new profiles are deeper than those given by former calculations and can modify the spectroscopic analysis when using high-quality observational data. The results are especially important for CPN. With the same method, the problem of the overlapping of H and ionized He lines is solved in a quantitative way for the first time. It is found that this overlapping has no importance in stellar atmospheres. It cannot explain, even partially, the 4686-A emission, nor has it influence over the optical profiles of both ions. Thus, the line formation calculations of H and He II may be performed separately, as has been done until now.

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