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

Groh, J. H., Oliveira, A. S., Steiner, J. E. 2008, A&A, 485, 245

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° ± 0.09°), HD 45166 is an ideal laboratory for wind-structure studies. The goal of the present paper is to determine the fundamental stellar and wind parameters of the qWR star. 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. Abundances and stellar and wind parameters of the qWR star were obtained. The qWR star has an effective temperature of T_eff = 50 000 ± 2000 K, a luminosity of log (L/Lsun) = 3.75 ± 0.08, and a corresponding photospheric radius of R_phot = 1.00 Rsun. 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 Mdot= 2.2 × 10-7 Msun yr-1, and the wind terminal velocity is v∞=425 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. The wind parameters determined are unusual when compared to O-type stars or to typical WR stars. While for WR stars v∞/v_esc > 1.5, in the case of HD 45166 it is much smaller (v∞/v_esc = 0.32). In addition, the efficiency of momentum transfer is η=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.