Volume 485, Number 1, July I 2008
|Page(s)||245 - 256|
|Published online||06 May 2008|
II. Fundamental stellar parameters and evidence of a latitude-dependent wind
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: firstname.lastname@example.org
2 Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, SP, Brazil
3 IP&D, Universidade do Vale do Paraíba, Av. Shishima Hifumi 2911, CEP 12244-000, São José dos Campos, SP, Brazil
4 SOAR Telescope, Casilla 603, La Serena, Chile
Accepted: 4 April 2008
Context. The enigmatic object HD 45166 is a qWR star in a binary system with an orbital period of 1.596 day, and presents a rich emission-line spectrum in addition to absorption lines from the companion star (B7 V). As the system inclination is very small (), HD 45166 is an ideal laboratory for wind-structure studies.
Aims. The goal of the present paper is to determine the fundamental stellar and wind parameters of the qWR star.
Methods. A radiative transfer model for the wind and photosphere of the qWR star was calculated using the non-LTE code CMFGEN. The wind asymmetry was also analyzed using a recently-developed version of CMFGEN to compute the emerging spectrum in two-dimensional geometry. The temporal-variance spectrum (TVS) was calculated to study the line-profile variations.
Results. Abundances and stellar and wind parameters of the qWR star were obtained. The qWR star has an effective temperature of K, a luminosity of , and a corresponding photospheric radius of . The star is helium-rich (N(H)/N(He) = 2.0), while the CNO abundances are anomalous when compared either to solar values, to planetary nebulae, or to WR stars. The mass-loss rate is , and the wind terminal velocity is km s-1. The comparison between the observed line profiles and models computed under different latitude-dependent wind densities strongly suggests the presence of an oblate wind density enhancement, with a density contrast of at least 8:1 from equator to pole. If a high velocity polar wind is present (~1200 km s-1), the minimum density contrast is reduced to 4:1.
Conclusions. The wind parameters determined are unusual when compared to O-type stars or to typical WR stars. While for WR stars , in the case of HD 45166 it is much smaller (). In addition, the efficiency of momentum transfer is , which is at least 4 times smaller than in a typical WR. We find evidence for the presence of a wind compression zone, since the equatorial wind density is significantly higher than the polar wind. The TVS supports the presence of such a latitude-dependent wind and a variable absorption/scattering gas near the equator.
Key words: stars: winds, outflows / stars: mass-loss / stars: fundamental parameters / binaries: spectroscopic / stars: individual: HD 45166 / stars: Wolf-Rayet
© ESO, 2008
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