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robin_astro

A Spectrum of Comet 46P Wirtanen

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A spectrum of Comet 46P (Wirtanen) with the ALPY600. 

 
46p_darksub_sum_cosrem.jpg.1251f7f83fad76e8414fcf0383cafc8b.jpg

The raw spectrum image before sky background subtraction. Note as well as the comet spectrum, the bright Na D line from local light pollution and other auroral lines from natural airglow

The coma extended beyond the length of the slit so a separate sky spectrum was recorded and subtracted


C46P_20181209_876_Leadbeater.png.dd659dec6687fa9511cb81c4ce1c2527.png

The Spectrum of the bright central region is dominated by the scattered light from the sun while the spectrum of the extended coma is mainly emission from excited molecules such as CN (The very bright line in the UV), C3,  C2 (The Swan bands which give the coma its blue green colour) and NH2

 

By removing the emission component from the spectrum of the central region and dividing it by the spectrum of a sunlike star recorded the same evening, the reflectance spectrum of the dust can be extracted

 
c46p_6arcsec_20181209_876_reflectance.png.4b771e5680b776232b23060a66b3ad2e.png

 

Robin

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This is very interesting, thanks for sharing! Can anything be concluded from the reflectance spectrum? Like dust components or density?

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Cool! Never thought of doing this. 

Edited by tooth_dr

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4 hours ago, Waddensky said:

Can anything be concluded from the reflectance spectrum? Like dust components or density?

I am not sure.  I need to find out more about interpreting comet spectra.   I believe you can estimate things like dust and gas production rates.  I was a little surprised at the reflectance spectrum. I expected enhanced scattering at the blue end (like interstellar dust and cigarette smoke)  but that probably just highlights my limited knowledge of comets ?

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Quite a collection of molecules. We are just seeing the shattered remains in the emission spectrum here, radicals dissociated by sunlight

Robin

Edited by robin_astro

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It is fascinating stuff!  like trying to do a jigsaw where you have little pieces and no picture...

Helen 

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I'm off to a conference on 46P next summer so it will be fascinating to see how much we learn from this close apparition.

Helen

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