The Blue Flash Nebula, NGC 6905, is a bright planetary nebula, covering about 1.2' of sky in Delphinus, roughly 7,500 light years away from us in space and time. The Blue Flash is a pretty typical planetary nebula, formed as an aging star ejected its outer shell, which is ionized by the intense UV radiation from the core, inducing the fluorescent glow from the expanded shell of gas. The central star, the source of the nebula, is a white dwarf with an estimated temperature of 150,000 K. The nickname Blue Flash was apparently first used by John Mallas, an amateur astronomer who wrote a series of articles about planetary nebulae in The Review of Popular Astronomy in the 1960s.The Blue Flash has strong green-blue OIII emission, but also emits in the red from Hapha, and toward the north and south ansae (the "handles" of the nebula) there is enhanced emission in the red from NII, see
Cuesta. However, my crude RGB values do not show the red contribution as the key to the color. The dust and gas may also be reflecting light, which would contribute to the more blue tone, in the same way that our sky looks blue? This is supported by the change I see in the G/B values from the core to the ansae. Aside from my speculation, I have not been able to find anything to explain the more blue tone, if anyone can help I would be fascinated to hear about it.
Comments