Resolving the Hα-emitting Region in the Wind of η Carinae

Abstract

The massive evolved star η Carinae is the most luminous star in the Milky Way and has the highest steady wind mass-loss rate of any known star. Radiative transfer models of the spectrum by Hillier et al. predict that Hα is mostly emitted in regions of the wind at radii of 6-60 AU from the star (2.5-25 mas at 2.35 kpc). We present diffraction-limited images (FWHM ∼ 25 mas) with Magellan adaptive optics (MagAO) in two epochs, showing that η Carinae consistently appears ∼2.5-3 mas wider in Hα emission compared to the adjacent 643 nm continuum. This implies that the Hα line-forming region may have a characteristic emitting radius of 12 mas or ∼30 AU, in very good agreement with the Hillier stellar-wind model. This provides direct confirmation that the physical wind parameters of that model are roughly correct, including the mass-loss rate ofṀ = 10 −3 M yr −1 , plus the clumping factor, and the terminal velocity. Comparison of the Hα images (ellipticity and PA) to the continuum images reveals no significant asymmetries at Hα. Hence, any asymmetry induced by a companion or by the primary's rotation do not strongly influence the global Hα emission in the outer wind.

Uncovering the orbital dynamics of stars hidden inside their powerful winds: application to η Carinae and RMC 140

“…The primary star is an LBV with an extremely powerful wind: a mass-loss rate of 8.5×10 −4 M yr −1 and terminal wind velocity of 420 km s −1 Groh et al 2012a;Clementel et al 2015a). Under these conditions, showed that H-alpha could be formed in an extended region between 6 − 60 AU (assuming R * = 60 R ) outwards from the primary, and these results have been observationally supported by Wu et al (2017). As a result, we know the primary star displays spectral lines formed in highly extended regions from the central star.…”

High-contrast Hα imaging with Subaru/SCExAO + VAMPIRES

“…6), though the difference is marginal compared with the Hα and continuum observations of η Carinae. 35 This feature represents either of the expected astrophysical feature-limb brightening of the shock feature at Hα-or the difference of PSFs at wavelengths between the Hα and the continuum filters. To further test whether our data reduction can be affected by an artifact (e.g.…”