A Lighthouse Effect in Eta Carinae

Abstract

We present a new model for the behavior of scattered time-dependent, asymmetric near-UV emission from the nearby ejecta of η Car. Using a 3-D hydrodynamical simulation of η Car's binary colliding winds, we show that the 3-D binary orientation derived by Madura et al. (2012) is capable of explaining the asymmetric near-UV variability observed in the Hubble Space Telescope Advanced Camera for Surveys/High Resolution Camera (HST ACS/HRC) F220W images of Smith et al. (2004b). Models assuming a binary orientation with i ~ 130 to 145 degrees, ω ~ 230 to 315 degrees, PAz ~ 302 to 327 degrees are consistent with the observed F220W near-UV images. We find that the hot binary companion does not significantly contribute to the near-UV excess observed in the F220W images. Rather, we suggest that a bore-hole effect and the reduction of Fe II optical depths inside the wind-wind collision cavity carved in the extended photosphere of the primary star lead to the time-dependent directional illumination of circum-binary material as the companion moves about in its highly elliptical orbit.

14 pages, 4 figures, 1 table. Accepted for publication in ApJL

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• The three-dimensional structure of the Eta Carinae Homunculus
• The fossil wind structures of Eta Carinae: changes across on 5.54-year cycle
• 3D radiative transfer simulations of Eta Carinae's inner colliding winds - I. Ionization structure of helium at apastron
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• 3D Radiative Transfer in $\eta$ Carinae: Application of the SimpleX Algorithm to 3D SPH Simulations of Binary Colliding Winds
• 3D radiative transfer simulations of Eta Carinae's inner colliding winds - II: Ionization structure of helium at periastron
• CO, Water, and Possible Methanol in Eta Carinae Approaching Periastron
• Spectroscopic Signatures of the Vanishing Natural Coronagraph of eta Carinae
• The orbital kinematics of eta Carinae over three periastra with a possible detection of the elusive secondary's motion
• The Interaction of the Eta Carinae Primary Wind with a Century Old Slow Equatorial Ejecta
• A Case Study in Astronomical 3-D Printing: The Mysterious Eta Carinae
• GRAVITY chromatic imaging of Eta Car's core
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