The shape and orientation of the Homunculus Nebula based on spectroscopic velocities

Doppler velocities give information about the three-dimensional shape and orientation of the bipolar ejecta of η Car. We report slit spectroscopy obtained using the Space Telescope Imaging Spectrograph (HST/STIS), with spatial resolution adequate for good models. These data allow an independent estimate of the distance to this object. Equatorial velocities, not clearly recognized in earlier work, provide the first definite measure of the bipolar inclination angle relative to our line of sight. Equatorial structure is arguably the most significant new spectroscopic result reported here, and some of the equatorial gas has higher and lower velocities which probably represent later and earlier ejection events. A range of bipolar lobe shapes fit the data reasonably well; the worst ambiguities result from the nature of the object more than from instrumental limitations.