  The massive evolved star Eta Carinae is the most luminous star in the Milky
Way and has the highest steady wind mass-loss rate of any known star. Radiative
transfer models of the spectrum by Hillier et al. predict that H-alpha is
mostly emitted in regions of the wind at radii of 6 to 60 AU from the star (2.5
to 25 mas at 2.35 kpc). We present diffraction-limited images (FWHM ~25 mas)
with Magellan adaptive optics in two epochs, showing that Eta Carinae
consistently appears ~2.5 to 3 mas wider in H-alpha emission compared to the
adjacent 643 nm continuum. This implies that the H-alpha line-forming region
may have a characteristic emitting radius of 12 mas or ~30 AU, in very good
agreement with the Hillier stellar-wind model. This provides direct
confirmation that the physical wind parameters of that model are roughly
correct, including the mass-loss rate of 10^-3 M_sun/yr, plus the clumping
factor, and the terminal velocity. Comparison of the H-alpha images
(ellipticity and PA) to the continuum images reveals no significant asymmetries
at H-alpha. Hence, any asymmetry induced by a companion or by the primary's
rotation do not strongly influence the global H-alpha emission in the outer
wind.
