The shape of η Carinae and LBV nebulae

Abstract

Stellar winds emitted by rotating massive stars may show two main components: firstly bipolar lobes with low density and fast wind, produced by the higher Teff and gravity at the poles ("geff-effect"); secondly, an equatorial disc with a slow dense wind, produced by the stronger opacities at the equator ("K-effect"). To see the possible role of this anisotropic wind on the shape of LBV nebulae, we calculate the distribution of the ejected matter in 2 simplified cases: 1) A brief shell ejection. We find that prolate and peanut-shaped hollow nebulae naturally form due to the geff-effect in rotating stars. 2) A constant wind for a long time. This produces prolate filled nebulae, with a possible strong disc when a bi-stability limit is crossed in the equatorial region. Thus, many features of the η Carinae and LBV nebulae are accounted for by the anisotropic ejection from rotating stars.