Integral-Field Spectroscopy of the Post Red Supergiant IRC +10420: evidence for an axi-symmetric wind

TL;DR

This study uses adaptive optics integral-field spectroscopy to reveal that the massive hypergiant IRC +10420 has an axi-symmetric wind structure, providing insights into its mass-loss geometry and evolutionary stage.

Contribution

The paper provides the first strong evidence for wind axi-symmetry in IRC +10420 using integral-field spectroscopy, challenging previous assumptions and suggesting a transition toward the B[e] supergiant phase.

Findings

Evidence for wind axi-symmetry based on spectral line variations.

Identification of outer nebula emission similar to η Carinae's Strontium Filament.

Indications of evolution toward the B[e] supergiant phase.

Abstract

We present NAOMI/OASIS adaptive-optics assisted integral-field spectroscopy of the transitional massive hypergiant IRC +10420, an extreme mass-losing star apparently in the process of evolving from a Red Supergiant toward the Wolf-Rayet phase. To investigate the present-day mass-loss geometry of the star, we study the appearance of the line-emission from the inner wind as viewed when reflected off the surrounding nebula. We find that, contrary to previous work, there is strong evidence for wind axi-symmetry, based on the equivalent-width and velocity variations of H$\alpha$ and Fe {\sc ii} $\lambda$6516. We attribute this behaviour to the appearance of the complex line-profiles when viewed from different angles. We also speculate that the Ti {\sc ii} emission originates in the outer nebula in a region analogous to the Strontium Filament of $\eta$ Carinae, based on the morphology of the line-emission. Finally, we suggest that the present-day axisymmetric wind of IRC +10420, combined with its continued blueward evolution, is evidence that the star is evolving toward the B[e] supergiant phase.