Observations of the early stages in the formation of an LBV shell

Luminous blue variables are massive stars that undergo a series of eruptive events through which they shed their outer layers before becoming Wolf-Rayet stars. During the eruptive events, their winds are denser and expand slower than in the non-eruptive state. In this paper we apply a model for the interaction of the post-eruption fast wind with the slower moving shell of dense material that was ejected during the 1994 eruption of HD 5980, a massive system located in the Small Magellanic Cloud. The model predicts a velocity for the working surface that is consistent with the velocity of insterstellar-like absorption features observed in HST/STIS spectra of 1999 and 2000, leading to the conclusion that we have witnessed for the first time the earliest stages of a circumstellar shell being formed around an LBV.