Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-05-08
Astronomy and Astrophysics
Astrophysics
7 pages, 9 figures, accepted for publication in A&A
Scientific paper
10.1051/0004-6361:20054489
Recent calculations and analyses of O star spectra have revealed discrepancies between theory and observations, and between different theoretical calculations, for the strength of optical HeI singlet transitions.We investigate the source of these discrepancies. Using a non-LTE radiative transfer code we have undertaken detailed test calculations for a range of O star properties. Our principal test model has parameters similar to those of the O9V star, 10 Lac. We show that the discrepancies arise from uncertainties in the radiation field in the HeI resonance transition near 584Angs. The radiation field at 584Angs. is influenced by model assumptions, such as the treatment of line-blanketing and the adopted turbulent velocity, and by the FeIV atomic data. It isshown that two FeIV transitions near 584Angs can have a substantial influence on the strength of the HeI singlet transitions. Because of the difficulty of modeling the HeI singlet lines, particularly in stars with solar metalicity, the HeI triplet lines should be preferred in spectral analyses. These lines are much less sensitive to model assumptions.
Hillier Desmond John
Lanz Thierry
Martins Fabrice
Najarro Francisco
Puls Jason
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