Monday, 9 January 2012

Spectrum of Wolf-Rayet Star

The Baader Planetarium spectroscope would not normally show detail in the spectrum of any star as faint as ~7mgv - but there are exceptions. This is one!  Years back I had seen the faint blue carbon line in the spectrum of star WR79 in rich galactic cluster NGC6231, close to Zeta Sco. Recently, after removing the cylindrical lens that broadens the spectrum - producing a prime spectrum - I had sucess seeing emission lines in the spectrum of Eta Carina (see post below)

The same setup, when used on N6231 produced this view. It was spectacular! This star is a Wolf-Rayet type WC6, of 6.7mgv. The bands are almost identical to the brightest WR star Gamma Velorum. The blue line is a blend of two carbon lines, as is the lemon-yellow line. The fainter orange line is due to helium. Kaler J. tells us the WR stars are helium burners - having used up their hydrogen through fusion and mass-loss - exposing a helium shell.  Carbon is a product of helium fusion - hence these gaudy bands.  A nice example of stellar physics in a rare star type.  No cameras used for this sketch - but software helped to create the colours.

The other cluster stars are all type O and B - and showed no details in my setup. There are several WR stars in the southern summer sky. I hope to sketch them soon.

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