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Comet 46P/Wirtanen spectrum

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About this observation
Observer
Hugh Allen
Time of observation
13/12/2018 - 21:00
Object
Comet 46P/Wirtanen
Observing location
Oakhill Somerset
Equipment
8" Meade LX90 at f6.3
Alpy 600 spectroscope
Atik 314L camera
BASS software
Tags

Spectrum of Comet 46P/Wirtanen in a clear(ish) sky on Thursday night. I would not describe the comet as particularly bright even in a telescope, its 5th magnitude being spread over a large surface. My unguided set-up struggled to pull much signal from above the noise even by keeping the bright nucleus on or near the slit. So for presentation I ran the final 1D spectrum through a weak Gaussian filter to smooth some of the noise and make the stronger features more visible. I also manually 'snipped' the sky background out of the spectrum rather than subtract the sky background which would have introduced even more noise (I snipped light pollution lines at 5461Å [mercury], 5577Å [oxygen airglow], and 5893Å [sodium]). Nevertheless, the 'classic' cometary emission lines are clearly visible: Swan emission bands from C₂ radicals, C₃ radicals, and an intense near-UV emission from CN radicals. Even NH₂ radicals can be identified. The spectrum is response corrected using the (then) nearby B9V star Xi Tau. All in all I found this a more difficult target than I expected.

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