1 Introduction

The star $\eta$ Car is one of the best studied, but still poorly understood members of the class of Luminous Blue Variables (Davidson & Humphreys 1997). $\eta$ Car shows a spectacular, strongly bipolar nebula referred to as the homunculus (e.g. Morse et al. 1998), that was created during the great eruption of 1840-1860. The homunculus is sometimes described as a hollow flask expanding with velocities between 400 and $\sim$800  $\rm km\,s^{-1}$. A conspicuous equatorial skirt is seen in the Hubble Space Telescope (HST) images. Proper motion studies of the condensations in the skirt show that these were ejected during the great eruption (Morse et al. 2001). There is strong evidence that $\eta$ Car is a binary star with a period of 5.52 years and orbital eccentricity of 0.6 (Damineli 1996; Damineli et al. 2000). The X-ray light curve of $\eta$ Car is consistent with a colliding winds model (Corcoran et al. 2001), and supports the binary model for $\eta$ Car.

Many studies have focused on infrared imaging of the dusty homunculus (e.g. Gehrz et al. 1973; Smith et al. 1998; Polomski et al. 1999, hereafter Pol99; Gehrz et al. 1999; Pantin & Le Mignant 2000, hereafter PL00). These studies show that at near-IR wavelengths the central star dominates while the lobes are faint. Note that speckle polarimetry of the core of $\eta$ Car indicates that the central star is not viewed directly but is obscured (Falcke et al. 1996). At mid-IR wavelengths several equatorial emission blobs northeast and southwest of the central star are visible. These blobs are interpreted as evidence for an equatorial torus (Pol99; Morris et al. 1999, hereafter Mor99). PL00 show that the bipolar lobes cannot be empty and suggest the presence of a second shell interior to the optically visible homunculus. HST observations also point to an inner structure (Ishibashi et al. 2000).

The Infrared Space Observatory (ISO) spectrum of $\eta$ Car (taken Jan. 1996) shows three spectral components: a power law between 2 and about 10 $\mu$m, arising from the central point source, a T $\sim$ 250 K component, attributed to the lobes, and a T $\sim$ 110-130 K component, attributed to a cold, $\sim$15 $M_{\odot}$ equatorial torus (Mor99). It was suggested that the massive equatorial torus was present before the great eruption and caused the highly bipolar shape of the nebula.

In this Letter we discuss new mid-IR images of $\eta$ Car that resolve the equatorial blobs and show that they have a highly symmetric ring-like shape with a surprising orientation with respect to the homunculus. The images may point to a drastic change in the orientation of the plane of symmetry of the system some time after the great eruption.