Numerical Modeling of η Carinae Bipolar Outflows

In this paper, we present two-dimensional gas dynamic simulations of theformation and evolution of the eta-Car bipolar outflows. Adopting theinteracting nonspherical winds model, we have carried out high-resolutionnumerical simulations, which include explicitly computed time-dependentradiative cooling, for different possible scenarios of the colliding winds. Inour simulations, we consider different degrees of non-spherical symmetry forthe pre-outburst wind and the great eruption of the 1840s presented by theeta-Car wind. From these models, we obtain important differences in the shapeand kinematical properties of the Homunculus structure. In particular, we findan appropriate combination of the wind parameters (that control the degree ofnon-spherical symmetry) and obtain numerical experiments that best match boththe observed morphology and the expansion velocity of the eta-Car bipolarshell. In addition, our numerical simulations show the formation of a bipolarnebula embedded within the Homunculus (the little Homunculus) developed from asecondary eruptive event suffered by the star in the 1890s, and also thedevelopment of tenuous, high velocity ejections in the equatorial region thatresult from the impact of the eruptive wind of the 1840s with the pre-outburstwind and that could explain some of the high speed features observed in theequatorial ejecta. The models were, however, unable to produce equatorialejections associated to the second eruptive event.Comment: 33 pages, 9 figures, accepted by the Astrophysical Journa