Multiple shell ejections on a 100 yr timescale from a massive yellow
  hypergiant
  This contribution focuses on a rare example of the class of post-Red
Supergiants, IRAS 17163-3907, the central star of the Fried Egg nebula. In
particular, we discuss some of our recently published results in detail. The
inner parts of the circumstellar environment of this evolved massive star are
probed at milli-arcsec resolution using VLTI's GRAVITY instrument operating in
the K-band (2 $\mu$m), while larger, arcsecond, scales are probed by VISIR
diffraction limited images around 10 $\mu$m, supplemented by a complete
Spectral Energy Distribution. The spectro-interferometric data cover important
diagnostic lines (Br$\gamma$, Na I), which we are able to constrain spatially.
Both the presence and size of the Na I doublet in emission has been
traditionally challenging to explain towards other objects of this class. In
this study we show that a two-zone model in Local Thermal Equilibrium can
reproduce both the observed sizes and strengths of the emission lines observed
in the K-band, without the need of a pseudo-photosphere. In addition, we find
evidence for the presence of a third hot inner shell, and demonstrate that the
star has undergone at least three mass-loss episodes over roughly the past
century. To explain the properties of the observed non-steady mass-loss we
explore pulsation-driven and line-driven mass-loss and introduce the
bi-stability jump as a possible underlying mechanism to explain mass-loss
towards Yellow Hypergiants.
