We have identified a ring-shaped emission-line nebula and a possible bipolar outflow centered on the B1.5 supergiant Sher # 25 in the Galactic giant H ii region NGC 3603 ( distance 6 kpc ) .
The clumpy ring around Sher # 25 appears to be tilted by 64 ^ { \circ } against the plane of the sky .
Its semi-major axis ( position angle \approx 165 ^ { \circ } ) is 6 . ^ { \prime \prime } 9 long , which corresponds to a ring diameter of 0.4 pc .
The bipolar outflow filaments , presumably located above and below the ring plane on either side of Sher # 25 , show a separation of \approx 0.5 pc from the central star .

High-resolution spectra show that the ring has a systemic velocity of V _ { LSR } = +19 km s ^ { -1 } and a de-projected expansion velocity of 20 km s ^ { -1 } , and that one of the bipolar filaments has an outflow speed of \sim 83 km s ^ { -1 } .
The spectra also show high [ N ii ] /H \alpha ratio , suggestive of strong N enrichment .
Sher # 25 must be an evolved blue supergiant ( BSG ) past the red supergiant ( RSG ) stage .
We find that the ratio of equatorial to polar mass-loss rate during the red supergiant phase was \approx 16 .
We discuss the results in the framework of RSG–BSG wind evolutionary models .

We compare Sher # 25 to the progenitor of SN 1987 A , which it resembles in many aspects .