The three-dimensional structure of the Eta Carinae Homunculus

• Published in: Monthly notices of the Royal Astronomical Society Vol. 442; no. 4; pp. 3316 - 3328
• Main Authors: Steffen, W., Teodoro, M., Madura, T. I., Groh, J. H., Gull, T. R., Mehner, A., Corcoran, M. F., Damineli, A., Hamaguchi, K.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 21-08-2014
• Subjects: Astronomy; Double stars; Morphology; Nebulae; stars: mass-loss; methods: numerical; stars: winds, outflows; circumstellar matter; stars: individual: Eta Carinae
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stu1088

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 H2 λ = 2.121 25 μm 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 (∼55°) and latitudinal (10°-20°) distances from the projected apastron direction of the binary orbit. The angular distance between the protrusions (∼110°) is similar to the angular extent of each polar trench (∼130°) and nearly equal to the opening angle of the wind–wind collision cavity (∼110°). 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.