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Go Back   IceInSpace > General Astronomy > Radio Astronomy and Spectroscopy

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Old 11-02-2013, 09:04 PM
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Comet 2012 F6 Lemon- A Spectroscopic Perspective

Dear All
I aimed my LISA spectrograph at this now very popular comet to see what it looked like.
Comets are illuminate mostly by reflected sunlight but the composition of the comet changes the spectra so you can detemine some common elements in the comet.
Most of the comet spectra comes from carbon compounds that have been vapourised from the surface of the comet. Many of these are known as Swan bands. There is also CN and CH compounds.

Another interesting effect is the width of the actual spectra. My spectra was taken by aligning the coma of the comet on the slit of the spectrograph. For a star this would create a spectra a few pixels high but because the comet has a diffuse coma then the spectra is broad with the spectra from the diffuse coma visible above and below the comet body spectra as a weakening band vertically. See the attached image.
Cheers

Terry
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Last edited by Terry B; 16-02-2013 at 04:51 PM.
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Old 11-02-2013, 09:09 PM
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Great stuff Terry

Pete
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Old 11-02-2013, 09:18 PM
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Good stuff, Terry.

Al.
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Old 13-02-2013, 11:12 PM
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Nice work Terry!
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Old 13-02-2013, 11:26 PM
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Interesting Terry,

What happens if you subtract a spectra of the sun from the comet spectra. Is that a valid way of identifying the "spikes due to the comet"?

DT
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Old 16-02-2013, 10:09 AM
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Fantastic work Terry, congratulations!

Here's my effort from this morning - no slit so I thought I'd do better at a wider scale (55mm) to reduce the comet to as small a size as possible. Bad logic, the spectrum reduces in scale too! Had issues with light cloud, heavy dew & car headlights in getting what I got. The severe vignetting is because I shot with an ordinary camera lens with the grating set in an old lens cap - it acts as a very restrictive aperture mask.

Anyway, pretty pleased, first time I've had a try at a comet. I 'borrowed' your calibration Terry as I haven't done a decent calibration for 55mm shots - thanks.

Cheers -
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Old 16-02-2013, 04:49 PM
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Very good Rob
Interesting that there is no evidence of the UV band in your images. I assume that the camera lens has a UV filter from the coating.

Cheers

Terry
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Old 16-02-2013, 05:01 PM
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Excellent results!
Well done guys.
It's great to see some first class cometary spectra.
It's obvious from the Swan bands, were the typical "green" comet emits it's light.
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Old 22-02-2013, 10:37 PM
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Quote:
Originally Posted by Terry B View Post
Very good Rob
Interesting that there is no evidence of the UV band in your images. I assume that the camera lens has a UV filter from the coating.

Cheers

Terry
Hi Terry - yes, I'd imagine that the filter would cut it. However I've been through the three subs I've got and there does seem to be a faint line there, which I've duly processed out with levels in the posted spectrum to hide noise!

Of the three subs, the first is by far the best, the other two being badly affected by cloud. So I just processed that sub, this time leaving noise & a stray faint star spectrum in. I've got the probable CN line arrowed in both the image and the bar spectrum. Judging by your spectrum, the Bayer filter on the camera (is it a Bayer filter?) has had a major impact on the CN line or it would be a bright dot in the image. Thanks for pointing this out!

I'm currently camera-less (waiting on a new DSLR) but I'll try to replicate this when it arrives, hopefully in better skies.

Cheers -
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Click for full-size image (C2012 F6, 15 Feb 2013, 17-40 UT spectrum bar b.jpg)
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Last edited by Rob_K; 23-02-2013 at 12:20 PM. Reason: Added pic
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