Radiative wind models with azimuthal symmetry - II. A latitude-dependent wind for Be and B[e] stars

Abstract

We present an axisymmetric radiative wind model in which we explore different contributions of thin and thick lines as a function of star latitude. The finite disc correction is incorporated in the line force. We also consider a viscosity parameter, which causes the wind to deviate from angular momentum conservation, and the effects of rapid rotation in the star itself. Numerical calculations for early Be stars give density contrasts between the equator and the pole that may be as high as 150 if a rotation rate of 90 per cent of the critical speed is assumed. If a lower rate is used (70 per cent), this density ratio decreases to about 15–20. Global mass losses, obtained from mass fluxes per unit solid angle in different directions, are in the range |$5 \times 10^{-9}-5\times 10^{-8} \text M _\odot\enspace \text {yr}^{-1}$|⁠. High velocities are still present in the equatorial plane. Terminal velocities in this region are about 1000–1300 km s−1, while polar values are 2300 km s−1. Application to B[e] supergiants leads to |$\upsilon_\infty \approx 650 \enspace\ \text {km} \enspace \text s ^{-1}$| (pole) and to |$\upsilon_\infty \approx 450-500 \enspace\ \text {km} \enspace \text s ^{-1}$| (equator). A significant equator–pole density contrast (about 30) is obtained even with moderate rotation rates, which could increase the degree of linear polarization in these objects.