Tracing a decade of activity towards a yellow hypergiant. The spectral and spatial morphology of IRC+10420 at au scales

ABSTRACT The fate of a massive star during the latest stages its evolution is highly dependent on mass-loss history and geometry, with yellow hypergiants (YHGs) being key objects. We present near-IR interferometric observations famous YHG IRC+10420 blue spectra taken between 1994 2019. Our 2.2-μm GRAVITY/VLTI attain spatial resolution ∼5 stellar radii spatially resolve hot emission in K-band tracing gas via Na i doublet Br γ emission. geometric modelling reveals compact neutral zone (Na i) which slightly larger than continuum but within an extended emitting region. study confirms hour-glass geometry wind, we find no signature companion at 7–800 au separations contrast limit our (3.7 mag 3σ) to explain this geometry. report ejecta over 7 yr, constrain opening angle be <10°. Lastly, first optical since 1994. multi-epoch data indicate that spectral type, thus temperature, object has essentially remained constant intervening years. Therefore, observed increase temperature 2000 K less two decades prior now halted. This suggests ‘hit’ White Wall HR-diagram preventing it from evolving blue-wards, will likely undergo major event near future.