Penetrating the Homunculus -- Near-Infrared Adaptive Optics Images of Eta Carinae

TL;DR

This study uses near-infrared adaptive optics imaging to reveal the complex, multi-epoch ejection structures around Eta Carinae, showing that the observed nebulae are composed of separate, spatially distinct clumps from different eruptions.

Contribution

It provides detailed imaging and analysis of the ejection history of Eta Carinae, clarifying the structure and timing of its past eruptions through high-resolution near-infrared observations.

Findings

The butterfly nebula consists of separate clumps ejected during different eruptions.

Proper motions indicate ejections occurred approximately during the great and second eruptions.

Most material is distributed above and below the equatorial plane, behind the Little Homunculus.

Abstract

Near-infrared adaptive optics imaging with NICI and NaCO reveal what appears to be a three-winged or lobed pattern, the "butterfly nebula", outlined by bright Br$\gamma$ and H$_{2}$ emission and light scattered by dust. In contrast, the [Fe II] emission does not follow the outline of the wings, but shows an extended bipolar distribution which is tracing the Little Homunculus ejected in $\eta$ Car's second or lesser eruption in the 1890's. Proper motions measured from the combined NICI and NaCO images together with radial velocities show that the knots and filaments that define the bright rims of the butterfly were ejected at two different epochs corresponding approximately to the great eruption and the second eruption. Most of the material is spatially distributed 10$\arcdeg$ to 20$\arcdeg$ above and below the equatorial plane apparently behind the Little Homunculus and the larger SE lobe. The equatorial debris either has a wide opening angle or the clumps were ejected at different latitudes relative to the plane. The butterfly is not a coherent physical structure or equatorial torus but spatially separate clumps and filaments ejected at different times, and now 2000 to 4000 AU from the star.