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Comet NEOWISE high resolution spectrum

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#26 robin_astro

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Posted 17 July 2020 - 05:52 AM

 

Against this background I'm really impressed with your contribution to this topic!

Thanks for bringing the subject up, something I was completely unaware of until you mentioned it.(I have some reading up to do!) The comet ratio should be reasonably reliable but the sky ratio will be mess of light pollution, atmospheric emission and solar spectrum absorption from the bright sky.

 

Robin



#27 stefan822

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Posted 18 July 2020 - 01:34 PM

Hi,
 
on Jul 14 I made this observation:
 
Colors od the gas tail

 

A point in the gas tail had been used for white balance. As mentioned in the description in the gallery and on the home page, the reddish component in the gas tail can not come from sodium because a light pollution filter had been used. The red sensitivity is approx. 650nm to 700nm. (Red enhanced Nikon D610 and Astronomik CLS filter in front of the lens)

 

On Internet I found this spectrum which was captured two days later:

 

http://www.wellsastr...200716_orig.png

 

In the relevant range there is no sign of any emission.

 

Has anyone an explanation?

 

Regards Stefan



#28 robin_astro

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Posted 18 July 2020 - 02:26 PM

Hi Stefan,

 

The red emission in the tail is very weak and would not show up strongly in this spectrum which preferentially covers the dust tail region  (The light sampled is the dark area covered by  the slit.) There are some emission bands in the red part of the spectrum as Christian Buil's high resolution spectrum shows here, (posibly NH2 as I mentioned up the thread) though this is of the coma, not the tail.

http://www.spectro-a....php?f=6&t=2578

I have some tail cross section spectra to process but they are close in to the coma so probably will not show the gas tail separate from the dust tail. I think it is going to be extremely difficult (for amateurs at least) to get a spectrum of the cross section of the gas tail where it has significantly diverged from the dust tail.

 

Cheers

Robin



#29 robin_astro

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Posted 18 July 2020 - 02:45 PM

The Sodium emission is reported to be weakening (as to be expected as the distance from the sun increases) so further images could be interesting

 

Robin



#30 stefan822

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Posted 18 July 2020 - 04:06 PM

Hi Robin,

 

if an element is in the gas tail I would also expect it in the coma, it must come from somewhere.

 

At 6300A my camera is still blind (transmission curve off the filter: https://www.astronom...k_cls_trans.png), but the spectrum from Christian Buil shows some emissions near 6600A. Other comets like http://www.astrosurf...lovejoy/obs.htm had NH2 emissions in the same region.

 

Regards Stefan

 

Edit: NH2 seems not to appear as ion. If found a catalog of emission lines there: http://web.gps.calte...et/echelle.html (where is CO+,CO2+?) H2O+ seems to be the only ion that appears in the relevant range.

 

Another publication https://www.lpi.usra...metsII/7019.pdf gives an overview about ion species (section 8). Authors state (see fig 7) that the ion spectrum is stronger tailwards than at optocenter, unlike I expected above.


Edited by stefan822, 19 July 2020 - 07:03 AM.


#31 robin_astro

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Posted 19 July 2020 - 05:52 AM

 

 

if an element is in the gas tail I would also expect it in the coma, it must come from somewhere.

 

 

Not all emission lines in the outer coma/tail appear in the inner coma spectrum though eg

 

http://www.spectro-a...6&t=2578#p14371

 

I'll ask Christian if he will publish the spectrum in  high resolution spectrum above 6400A.  It might be possible to identify the lines there.

 

Cheers

Robin



#32 stefan822

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Posted 19 July 2020 - 07:10 AM

Not all emission lines in the outer coma/tail appear in the inner coma spectrum though eg

 

http://www.spectro-a...6&t=2578#p14371

 

I'll ask Christian if he will publish the spectrum in  high resolution spectrum above 6400A.  It might be possible to identify the lines there.

 

Cheers

Robin

 

I just edited my previous post and did not noticed your new post. Please see there.



#33 robin_astro

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Posted 19 July 2020 - 11:03 AM

Stefan

 

I am now processing my tail spectra from last week. See 

https://www.cloudyni...um-of-the-tail/

No sign of any strong red emission component yet but I am still looking :-)

 

(H2O+ is a possibility I  tentatively identified one of the emission lines lines as H2O+ in my high resolution spectrum of the yellow region but I was not certain)

 

Robin




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