A companion as the cause of latitude-dependent effects in the wind of
  Eta Carinae
  We analyze spatially resolved spectroscopic observations of the Eta Carinae
binary system obtained with HST/STIS. Eta Car is enshrouded by the dusty
Homunculus nebula, which scatters light emitted by the central binary and
provides a unique opportunity to study a massive binary system from different
vantage points. We investigate the latitudinal and azimuthal dependence of
H$\alpha$ line profiles caused by the presence of a wind-wind collision (WWC)
cavity created by the companion star. Using two-dimensional radiative transfer
models, we find that the wind cavity can qualitatively explain the observed
line profiles around apastron. Regions of the Homunculus which scatter light
that propagated through the WWC cavity show weaker or no H alpha absorption.
Regions scattering light that propagated through a significant portion of the
primary wind show stronger P Cygni absorption. Our models overestimate the H
alpha absorption formed in the primary wind, which we attribute to
photoionization by the companion, not presently included in the models. We can
qualitatively explain the latitudinal changes that occur during periastron,
shedding light on the nature of Eta Car's spectroscopic events. Our models
support the idea that during the brief period of time around periastron when
the primary wind flows unimpeded toward the observer, H alpha absorption occurs
in directions toward the central object and Homunculus SE pole, but not toward
equatorial regions close to the Weigelt blobs. We suggest that observed
latitudinal and azimuthal variations are dominated by the companion star via
the WWC cavity, rather than by rapid rotation of the primary star.
