The three-dimensional structure of the Eta Carinae Homunculus

We investigate, using the modelling code shape, the three-dimensional structure of the bipolar Homunculus nebula surrounding Eta Carinae as mapped by new ESO Very Large Telescope/X-Shooter observations of the H-2 lambda = 2.121 25 mu m emission line. Our results reveal for the first time important deviations from the axisymmetric bipolar morphology: (1) circumpolar trenches in each lobe positioned point symmetrically from the centre and (2) off-planar protrusions in the equatorial region from each lobe at longitudinal (similar to 55A degrees) and latitudinal (10A degrees-20A degrees) distances from the projected apastron direction of the binary orbit. The angular distance between the protrusions (similar to 110A degrees) is similar to the angular extent of each polar trench (similar to 130A degrees) and nearly equal to the opening angle of the wind-wind collision cavity (similar to 110A degrees). As in previous studies, we confirm a hole near the centre of each polar lobe and no detectable near-IR H-2 emission from the thin optical skirt seen prominently in visible imagery. We conclude that the interaction between the outflows and/or radiation from the central binary stars and their orientation in space has had, and possibly still has, a strong influence on the Homunculus. This implies that prevailing theoretical models of the Homunculus are incomplete as most assume a single-star origin that produces an axisymmetric nebula. We discuss how the newly found features might be related to the Homunculus ejection, the central binary, and the interacting stellar winds.