  Luminous Blue Variables have been suggested to be the direct progenitors of
supernova types IIb and IIn, with enhanced mass loss prior to explosion.
However, the mechanism of this mass loss is not yet known. Here, we investigate
the qualitative behaviour of theoretical stellar wind mass-loss as a function
of Teff across two bi-stability jumps in blue supergiant regime and also in
proximity to the Eddington limit, relevant for LBVs. To investigate the
physical ingredients that play a role in the radiative acceleration we
calculate blue supergiant wind models with the CMFGEN non-LTE model atmosphere
code over an effective temperature range between 30000 and 8800 K. Although our
aim is not to provide new mass-loss rates for BA supergiants, we study and
confirm the existence of two bi-stability jumps in mass-loss rates predicted by
Vink, de Koter, & Lamers (1999). However, they are found to occur at somewhat
lower Teff (20000 and 9000 K, respectively) than found previously, which would
imply that stars may evolve towards lower Teff before strong mass-loss is
induced by the bi-stability jumps. When the combined effects of the second
bi-stability jump and the proximity to Eddington limit are accounted for, we
find a dramatic increase in the mass-loss rate by up to a factor of 30. Further
investigation of both bi-stability jumps is expected to lead to a better
understanding of discrepancies between empirical modelling and theoretical
mass-loss rates reported in the literature, and to provide key inputs for the
evolution of both normal AB supergiants and LBVs, as well as their subsequent
supernova type II explosions.
