The three-dimensional structure of the Eta Carinae Homunculus

W. Steffen$^1$, M. Teodoro$^2$, T. I. Madura$^2$, J. H. Groh$^3$, T. R. Gull$^2$, A. Mehner$^4$, M. F. Corcoran$^{5,6}$, A. Damineli$^7$, and K. Hamaguchi$^{5,8}$

1 - Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo Postal 106, Ensenada 22800, Baja California, México; 2 - Astrophysics Science Division, Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA; 3 - Geneva Observatory, Geneva University, Chemin des Maillettes 51, CH-1290 Sauverny, Switzerland; 4 - ESO, Alonso de Cordova 3107, Vitacura, Santiago de Chile, Chile; 5 - CRESST and X-ray Astrophysics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA; 6 - Universities Space Research Association, 7178 Columbia Gateway Drive, Columbia, MD 21046, USA; 7 - Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil; 8 - Department of Physics, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA

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.

Reference: Published on MNRAS (August 11, 2014) 442 (4): 3316-3328.
doi: 10.1093/mnras/stu1088
First published online July 7, 2014
Status: Other