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Microturbulence in O supergiants

Smith, KC; Howarth, ID; (1998) Microturbulence in O supergiants. Monthly Notices of the Royal Astronomical Society , 299 (4) 1146 - 1158. 10.1046/j.1365-8711.1998.01873.x. Green open access

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We investigate the role of classical microturbulence in the non-LTE He i/He ii line formation problem for luminous O-type stars. We find that the shapes and strengths of certain saturated He i lines, in particular the triplets λλ4471, 4713 and the singlet λ4921, are sensitive to microturbulent velocities in excess of 5 km s−1. Weaker lines, including most of the He i singlets, are effectively independent of this parameter, as are the Fowler series He ii lines λλ4199, 4541, 5411. We show that this behaviour is due to interaction between direct line-broadening effects in the radiative transfer, and indirect changes in the atmospheric structure and the populations of absorbing states. Using an analysis of high-resolution, high signal-to-noise ratio observations of the O9.7 supergiant HD 152003 as an illustrative example, we show how the introduction of microturbulence in non-LTE models allows consistent fits to be obtained for all blue-region He i lines — including the strong triplets λλ4026, 4713, 4471 — at an assumed solar helium abundance, thereby offering a resolution to the problem of the ‘generalized dilution effect’ described by Voels et al. We argue that by extension this result may also have implications for the so-called ‘helium discrepancy’ identified in OB-type stars by Herrero et al.

Type: Article
Title: Microturbulence in O supergiants
Open access status: An open access version is available from UCL Discovery
DOI: 10.1046/j.1365-8711.1998.01873.x
Publisher version: http://dx.doi.org/10.1046/j.1365-8711.1998.01873.x
Language: English
Keywords: Line: formation, turbulence, Stars: abundances, Stars: atmospheres, Stars: early type, supergiants
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/144332
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