The qWR star HD 45166

Abstract

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• ± 0.09 • ), 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 twodimensional 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 eff = 50 000 ± 2000 K, a luminosity of log(L/L ) = 3.75 ± 0.08, and a corresponding photospheric radius of R phot = 1.00 R . 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 isṀ = 2.2 × 10 −7 M 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. Conclusions. 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.

Medium resolution spectroscopy of the supergiant O31f Cyg OB2 No. 7

“…Asymmetric winds were found in objects that are evolutionary related to O-stars: Luminous Blue Variables (LBV) (Groh et al 2006(Groh et al , 2010 and Wolf-Rayet stars (Harries et al 1998). Moreover numerical calculations Groh et al (2008) have shown that density of the wind of qWR star HD 45166 varies with latitude. We assume that the difference between the model describing Hα and the one describing CIV and NIV lines is related to a latitudinal inhomogeneity of the supergiant wind due to its rotation (V sin i = 105 km s −1 ).…”

Winds from stripped low-mass helium stars and Wolf-Rayet stars

“…Arguably the best example of a stripped star is HD 45166, which consists of a 4 M quasi-WR (qWR) star orbiting a B7V companion (Groh et al 2008), which may have evolved from a 12 M primary (Götberg et al 2017). HD 45166 has a surprisingly low (equatorial)) terminal wind velocity of 350 km s −1 .…”

Progenitors of supernova Ibc: a single Wolf-Rayet star as the possible progenitor of the SN Ib iPTF13bvn

“…These progenitors would in principle be much fainter (because they have low mass) than the detection limit of the pre-explosion images. For instance, low-mass binary stars known as V Sagittae stars (Steiner & Oliveira 2005), such as HD 45166 (Groh et al 2008), have been suggested as SN Ibc progenitors (E13). As shown by Groh et al (2008), these stars have relatively low luminosities (log (L /L ) = 3.75) and high effective temperatures (T eff = 50 000 K), so they would be undetectable in the pre-explosion images.…”