High-resolution optical spectroscopy of the sharp-lined B-type star HD 83206 |
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| Authors: | N Lehner P L Dufton D L Lambert R S I Ryans F P Keenan |
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| Institution: | Department of Pure and Applied Physics, The Queen's University, Belfast BT7 1NN; Department of Astronomy, The University of Texas at Austin, Austin, TX 78712-1083, USA |
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| Abstract: | Very-high-resolution ( R ～160 000) spectroscopic observations are presented for the early B-type star, HD 83206. Because it has very sharp metal lines, this star affords an opportunity to test theories of model atmospheres and line formation. Non-LTE model atmosphere calculations have been used to estimate the atmospheric parameters and absolute metal abundances (C, N, O, Mg and Si); an LTE analysis was also undertaken to investigate the validity of this simpler approach and to estimate an iron abundance. For the non-LTE calculations, there is excellent agreement with observations of the Balmer lines H α and H δ and the lines of Si ii and Si iii for atmospheric parameters of T eff?21 700±600 K and log g ?4.00±0.15 dex. The agreement is less convincing for the LTE calculations, and a higher gravity is deduced. Careful comparison of the metal line profiles with non-LTE calculations implies that the projected rotational and microturbulent velocities have maximum values of ?5 and ?2 km s?1, respectively. The latter value is smaller than has often been adopted in LTE model atmosphere analyses of main-sequence stars. Non-LTE absolute metal abundances are estimated, and a comparison with those for normal B-type stars (deduced using similar non-LTE techniques) shows no significant differences. A comparison of the abundances deduced using non-LTE and LTE calculations implies systematic differences of 0.1–0.2 dex, showing the importance of using a non-LTE approach when accurate absolute abundances are required. Its location in the Hertzsprung–Russell diagram and normal metal abundance lead us to conclude that HD 83206 is probably a main-sequence B-type star. As such, it is among the sharpest-lined young B-type star discovered to date. |
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| Keywords: | stars: abundances stars: atmospheres stars: early-type stars: individual: HD 83206 |
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