2002A&A...389L..65C

We report the discovery of the η Carinae ``Ghost Shell'', a high-velocity, spatially extended emission feature that lies in front of the southeast lobe of the η Carinae Homunculus. Using data obtained with ``Kueyen'', one of the European Southern Observatory's Very Large Telescope 8.2m telescopes and its Ultraviolet and Visible Echelle Spectrograph instrument, we have observed a structure in velocity space of width ≃35km/s and with Doppler velocities ranging from -675≤v≤-850km/s. This is up to 500km/s faster than the Homunculus front wall. The structure is distinct from the front wall in velocity space, and extends beyond the Homunculus' spatial boundaries. The Ghost Shell has been detected in emission for multiple allowed Balmer lines and in forbidden lines of [NII], [SII], and [ArIII]. The feature is also associated with a complex absorption structure in Ca H and K lines. We propose that the Ghost Shell lies outside the Homunculus and represents the forward shock between the fast stellar wind of the Great Eruption epoch and the older slow massive stellar wind.