# Resolving the H-alpha-emitting Region in the Wind of Eta Carinae

## TL;DR

This study uses high-resolution imaging to directly measure the H-alpha emitting region in Eta Carinae's wind, confirming predictions from radiative transfer models and providing insights into the star's wind structure and parameters.

## Contribution

First direct imaging confirmation of the H-alpha emission region size in Eta Carinae's wind, validating stellar wind models and their parameters.

## Key findings

- H-alpha emission region is about 12 mas (~30 AU) in radius.
- The observed size agrees with the Hillier stellar-wind model.
- No significant asymmetries in H-alpha emission related to the companion or rotation.

## Abstract

The massive evolved star Eta 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 H-alpha is mostly emitted in regions of the wind at radii of 6 to 60 AU from the star (2.5 to 25 mas at 2.35 kpc). We present diffraction-limited images (FWHM ~25 mas) with Magellan adaptive optics in two epochs, showing that Eta Carinae consistently appears ~2.5 to 3 mas wider in H-alpha emission compared to the adjacent 643 nm continuum. This implies that the H-alpha 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 of 10^-3 M_sun/yr, plus the clumping factor, and the terminal velocity. Comparison of the H-alpha images (ellipticity and PA) to the continuum images reveals no significant asymmetries at H-alpha. Hence, any asymmetry induced by a companion or by the primary's rotation do not strongly influence the global H-alpha emission in the outer wind.