Physical and wind properties of Galactic B supergiants are presented based upon non-LTE line blanketed model atmospheres , including Sher 25 toward the NGC 3603 cluster .
We compare H \alpha derived wind densities with recent results for SMC B supergiants and generally confirm theoretical expectations for stronger winds amongst Galactic supergiants .
Mid B supergiant winds are substantially weaker than predictions from current radiatively driven wind theory , a problem which is exacerbated if winds are already clumped in the H \alpha line forming region .
We find that the so-called ‘ bistability jump ’ at B1 ( \mathit { T } _ { eff } \sim 21kK ) from Lamers et al .
is rather a more gradual downward trend .
CNO elemental abundances , including Sher 25 , reveal partially processed material at their surfaces .
In general , these are in good agreement with evolutionary predictions for blue supergiants evolving redward accounting for rotational mixing .
A few cases , including HD 152236 ( \zeta ^ { 1 } Sco ) , exhibit strongly processed material which is more typical of Luminous Blue Variables .
Our derived photospheric [ N/O ] ratio for Sher 25 agrees with that for its ring nebula , although a higher degree of CNO processing would be expected if the nebula originated during a red supergiant phase , as is suspected for the ring nebula ejected by the B supergiant progenitor of SN 1987A , Sk–69 ^ { \circ } 202 .
Sher 25 has an inferred age of \sim 5Myr in contrast with \sim 2Myr for HD 97950 , the ionizing cluster of NGC 3603 , so it may be a foreground object or close binary evolution may be responsible for its unusual location in the H-R diagram .