The three-dimensional structure of the Eta Carinae Homunculus

TL;DR

This study uses 3D modeling and new observations to reveal complex, non-axisymmetric features in the Eta Carinae Homunculus nebula, challenging previous single-star models and highlighting the influence of binary interactions.

Contribution

First detailed 3D structural analysis of the Homunculus revealing deviations from axisymmetry and binary influence, using the SHAPE modeling code and ESO VLT/X-Shooter data.

Findings

Identification of circumpolar trenches in each lobe

Detection of off-planar protrusions in the equatorial region

Confirmation of polar holes and absence of near-IR H2 emission from the optical skirt

Abstract

We investigate, using the modeling code SHAPE, the three-dimensional structure of the bipolar Homunculus nebula surrounding Eta Carinae, as mapped by new ESO VLT/X-Shooter observations of the H2 $\lambda=2.12125$ micron 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 center and 2) off-planar protrusions in the equatorial region from each lobe at longitudinal (~55 degrees) and latitudinal (10-20 degrees) distances from the projected apastron direction of the binary orbit. The angular distance between the protrusions (~110 degrees) is similar to the angular extent of each polar trench (~130 degrees) and nearly equal to the opening angle of the wind-wind collision cavity (~110 degrees). 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. We also include a 3D printable version of our Homunculus model.