Iron-line diagnostics in the extreme colliding-wind binary Eta Carinae

Abstract by Jean-Christophe Leyder
Eta Carinae, one of the most peculiar objects in our Galaxy, was the second brightest object in the sky during its eruption in 1843. The large quantities of matter that were ejected at that time are now forming an extended nebula, while Eta Car is still ejecting matter through energetic stellar winds. Eta Car is a colliding-wind binary system: the dense stellar wind coming from the massive luminous blue variable primary star collides with the higher-velocity, lower-density wind from the hotter and luminous (and otherwise unseen) companion star in a highly eccentric orbit. Monitoring observations in the radio, UV, optical, and X-ray domains all indicate an orbital period of 5.5 years.

X-ray observations of a colliding-wind binary system such as Eta Carinae provide numerous clues as to the shock physics and mechanisms responsible for particle acceleration and emission in the hydrodynamical shocks that form between the stellar winds. Furthermore, Eta Carinae's long period and high eccentricity provides varying physical conditions, and allow to probe a large parameter space of densities and wind speeds, especially when observing periastron passages where strong variations occur over a short timescale.

In this talk, I will present a set of 23 high-resolution X-ray spectra of Eta Carinae obtained by the Chandra satellite, with a particularly detailed coverage around the X-ray minima of 2003.5 and 2009. I will focus on the variations and peculiarities observed in the Fe K line region. First noticed by Hamaguchi et al. 2007, the existence of a variable “red wing” in the profile of the Fe XXV triplet is puzzling. I will discuss possible hypothesis for the unexpected presence of such a "red wing" : the presence of an extremely bright, relatively cool, and heavily absorbed equilibrium plasma; emission due to unshocked photoionized wind material; or the possibility that a fraction of the thermal plasma is not in ionization equilibrium.

Background Papers
"X-Ray Spectral Variation of Eta Carinae through the 2003 X-Ray Minimum"
Hamaguchi K. et al. 2007

"Recent X-ray Variability of Eta Carinae: The Quick Road to Recovery"
Corcoran M.F. et al. 2010

"Chandra X-Ray Grating Spectrometry of Eta Carinae near X-Ray Minimum. I. Variability of the Sulfur and Silicon Emission Lines"
Henley D.B. et al. 2008

"Bulk Velocities, Chemical Composition, and Ionization Structure of the X-Ray Shocks in WR 140 near Periastron as Revealed by the Chandra Gratings"
Pollock A.M.T. et al. 2005