  The most massive stars, with initial masses above ~50M_sun, encounter a phase
of extreme mass loss - sometimes accompanied by so-called giant eruptions - in
which the stars' evolution is reversed from a redward to a blueward motion in
the HRD. In this phase the stars are known as Luminous Blue Variable
(LBVs).Neither the reason for the onset of the strong mass loss nor the cause
for the giant eruptions is really understood, nor is their implications for the
evolution of these most massive stars. I will present a study of the LBV
nebulae which are formed in this phase as a consequence of the strong mass loss
and draw conclusions from the morphology and kinematics of these nebulae on
possible eruption mechanisms and stellar parameters of the LBV stars. The
analysis contains a large collection of LBV nebulae which form an evolutionary
sequence of LBV nebulae. A special concern will be the frequently observed
bipolar nature of the LBV nebulae which seems to be a general feature and
presents strong constraints on further models of the LBV phase and especially
on the formation mechanism of the nebulae.

Astrophysics