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Cat's Eye Nebula

NGC 6543

The Cat's Eye Nebula (NGC 6543) is a planetary nebula in the Draco constellation estimated to be 1000 years old.

It as discovered by William Herschel on February 15 1786, and was the first planetary nebula whose spectrum was investigated, by the English amateur astronomer William Huggins in 1864. NGC 6543 is situated almost exactly in the direction of the North Ecliptic Pole. While the nebula, with its 20 arc second diameter, is rather small, it has an extended halo of matter the progenitor star has ejected during its red giant phase. This halo measures 386 arc seconds (5.8 arc min).

A preliminary interpretation suggests that the star might be a double star system. The dynamical effects of two stars orbiting one another most easily explains the intricate structures, which are much more complicated than features seen in most planetary nebulae. According to this model, a fast stellar wind of gas blown off the central star created the elongated shell of dense, glowing gas. This structure is embedded inside two larger lobes of gas blown off the star at an earlier phase. These lobes are "pinched" by a ring of denser gas, presumably ejected along the orbital plane of the binary companion.

The suspected companion star also might be responsible for a pair of high- speed jets of gas that lie at right angles to this equatorial ring. If the companion were pulling in material from a neighboring star, jets escaping along the companion's rotation axis could be produced.

These jets would explain several puzzling features along the periphery of the gas lobes. Like a stream of water hitting a sand pile, the jets compress gas ahead of them, creating the "curlicue" features and bright arcs near the outer edge of the lobes. The twin jets are now pointing in different directions than these features. This suggests the jets are wobbling, or precessing, and turning on and off episodically.