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We analyze spatially resolved spectroscopic observations of the Eta Carinaebinary system obtained with HST/STIS. Eta Car is enshrouded by the dustyHomunculus nebula, which scatters light emitted by the central binary andprovides a unique opportunity to study a massive binary system from differentvantage points. We investigate the latitudinal and azimuthal dependence ofH$\alpha$ line profiles caused by the presence of a wind-wind collision (WWC)cavity created by the companion star. Using two-dimensional radiative transfermodels, we find that the wind cavity can qualitatively explain the observedline profiles around apastron. Regions of the Homunculus which scatter lightthat propagated through the WWC cavity show weaker or no H alpha absorption.Regions scattering light that propagated through a significant portion of theprimary wind show stronger P Cygni absorption. Our models overestimate the Halpha absorption formed in the primary wind, which we attribute tophotoionization by the companion, not presently included in the models. We canqualitatively explain the latitudinal changes that occur during periastron,shedding light on the nature of Eta Car's spectroscopic events. Our modelssupport the idea that during the brief period of time around periastron whenthe primary wind flows unimpeded toward the observer, H alpha absorption occursin directions toward the central object and Homunculus SE pole, but not towardequatorial regions close to the Weigelt blobs. We suggest that observedlatitudinal and azimuthal variations are dominated by the companion star viathe WWC cavity, rather than by rapid rotation of the primary star.

A companion as the cause of latitude-dependent effects in the wind of Eta Carinae