The qWR star HD 45166 II. Fundamental stellar parameters and evidence of a latitude-dependent wind

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 (i=0.77 {\circ} pm 0.09 {\circ}), HD 45166 i...

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Published in:Astronomy and astrophysics (Berlin) 2008-07, Vol.485 (1), p.245-256
Main Authors: GROH, J. H, OLIVEIRA, A. S, STEINER, J. E
Format: Article
Language:English
Subjects:
Astronomy
Earth, ocean, space
Exact sciences and technology
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Summary: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 (i=0.77 {\circ} pm 0.09 {\circ}), 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 T_{\rm eff} = 50\,000 pm 2000 K, a luminosity of mathrm{log} (L/ {L}_{\odot}) = 3.75 pm 0.08, and a corresponding photospheric radius of R_{\rm phot} = 1.00 6{R}_{\odot}. 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 dot{M}= 2.2 X 10 {M}_{\odot}\,{\rm yr}, and the wind terminal velocity is v_{\infty}=425 km s super(-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 ( similar to 1200 km s super(-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 1.5$ v_{\infty}/v_{\rm esc} > 1.5, in the case of HD 45166 it is much smaller (v_{\infty}/v_{\rm esc} = 0.32). In addition, the efficiency of momentum transfer is eta=0.74, 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.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361:200809511