A Lighthouse Effect in Eta Carinae

Thomas I. Madura and Jose H. Groh

Max Planck Institute for Radio Astronomy, Bonn, Germany

We present a new model for the behavior of scattered time-dependent, asymmetric near-UV emission from the nearby ejecta of Eta Car. Using a 3-D hydrodynamical simulation of Eta 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, {omega} ~ 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.

Reference: Accepted for publication in ApJL. Pre-print available on astro-ph.
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1201.1848


Email: tmadura@mpifr-bonn.mpg.de