Object of the Week February 09, 2020 - WR bubble Sharpless 2-308
Sh 2-308 (= LBN 1052, WR 6, RCW 11)
WR nebula in CMa
RA: 06 54 13
DEC: -23 55 42
Size: ~35’
Deep down in CMa around 3,7' SE of Messier 41 we find one of the nicest and perfect shaped Wolf-Rayet (WR) bubble in the winter sky.
Around the very hot EZ CMa (HD 50896) we can find a full moon sized bubble. Science suspects a binary system because of the variation in brightness between 6,71 and 6,95mag. The bubble itself is emitted and ionized by UV-radiation of the hot WR star. This star is near its end and will pass away as an early supernova.
At the southern end of the bubble we can find another bright star, ο1 CMa. This 3,9mag red super giant once was supposed to be related with EZ CMa. Modern Hipparcos parallax placed the star in front (610pc) of the bubble around EZ CMa (1500pc). All in all ο1 CMa seems to associated with Collinder 121 south of Sh 2-308.
From the observable standpoint Sh 2-308 is a spectacular object. A little difficult for European observer (-24° DEC) its stands well in the North American sky. The Brightest part can be found to the east. Challenge is to see the bubble as a full circle because of its fainter SW side. Telescopes with larger fields shows the surrounded IFN. Mel Bartels could detect some brightening south and north of the nebula. Perhaps he can contribute some more information to his observation and sketch.
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