The three-dimensional structure of the Eta Carinae Homunculus

Abstract

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 theH2 λ = 2.121 25 μmemission 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 (~55{ring operator}) and latitudinal (10{ring operator}-20{ring operator}) distances from the projected apastron direction of the binary orbit. The angular distance between the protrusions ((~110{ring operator}) is similar to the angular extent of each polar trench ((~130{ring operator}) and nearly equal to the opening angle of the wind-wind collision cavity ((~110{ring operator}). As in previous studies, we confirm a hole near the centre of each polar lobe and no detectable near-IR H2 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. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.