Thomas I. Madura, Jose H. Groh
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.
View original:
http://arxiv.org/abs/1201.1848
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