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Comet NEOWISE high resolution spectrum

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#1 robin_astro

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Posted 11 July 2020 - 05:09 AM

The comet is now visible from the observatory so I have changed over from my simple portable Star Analyser setup

https://www.cloudyni...ser/?p=10319586

to the telescope mounted slit spectrogaphs. 

 

This is what the raw spectrum image looked like last night in the region around the Sodium D lines at ~0.4A resolution (LHIRESIII slit spectrograph with a 2400l/mm grating covering ~150 A).  The inset image is from the guide camera to show the position of the slit.

 

F3_raw_LHIRES2400_20200710.png

 

I have over exposed the coma in this image to bring out the detail in the spectrum of the tail.  The sodium emission is very intense but there is also some weaker molecular emission lines present. (To be identified once I have wavelength calibrated using the  spectrograph internal Ne/Ar lamp). Note the blue Doppler shift  in the Na D emission lines relative to lines in the sky background due to the comet's motion.

 

Cheers
Robin


Edited by robin_astro, 11 July 2020 - 05:09 AM.

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#2 ButterFly

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Posted 11 July 2020 - 05:17 AM

Excellent.

 

Someone posted a shot of the ion tail yesterday.  That vs. dust tail would be awesome.  They should separate more by the time it passes to evening.



#3 robin_astro

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Posted 11 July 2020 - 06:07 AM

 

Someone posted a shot of the ion tail yesterday.  That vs. dust tail would be awesome.  They should separate more by the time it passes to evening.

Does that show a sodium tail separate from the dust and gas tails as in Hale Bopp for example ?

https://en.wikipedia...opp#Sodium_tail

I need to try for a spectrum with the slit running across the tail to give a cross section of the distribution of dust, gas and sodium but the weather prospect are not good here

 

Robin


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#4 ButterFly

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Posted 11 July 2020 - 07:10 AM

There may be two ion tails.



#5 robin_astro

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Posted 11 July 2020 - 07:31 AM

There may be two ion tails.

An image taken with a narrow band NaD pass filter could be interesting. Not common among amateurs though I guess. The inverse filter response is more common !


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#6 RobboK

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Posted 11 July 2020 - 08:10 AM

Does that show a sodium tail separate from the dust and gas tails as in Hale Bopp for example ?

https://en.wikipedia...opp#Sodium_tail

I need to try for a spectrum with the slit running across the tail to give a cross section of the distribution of dust, gas and sodium but the weather prospect are not good here

 

Robin

I once had a rough (!!!) go at the tail of C/2011 L4 (PANSTARRS) which had a sodium tail.  No slit but the tail orientation gave me faint spectral 'slices' which showed strong sodium emission at least a short distance out along the tail of the comet.  Not quite what you're talking about so I look forward to your results Robin.

 

Cheers -

 

Rob

 

C2011 L4 spectrum, 01 Mar 2013, 10-08 UT head+tail-sections graph textredsm.jpg


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#7 robin_astro

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Posted 11 July 2020 - 09:43 AM

I once had a rough (!!!) go at the tail of C/2011 L4 (PANSTARRS) which had a sodium tail.  No slit but the tail orientation gave me faint spectral 'slices' which showed strong sodium emission at least a short distance out along the tail of the comet.  Not quite what you're talking about so I look forward to your results Robin.

 

Cheers -

 

Rob

 

attachicon.gifC2011 L4 spectrum, 01 Mar 2013, 10-08 UT head+tail-sections graph textredsm.jpg

Hi Rob,

 

Ah yes I remember that spectrum. I sometimes show it in my spectroscopy talks, with credit of course :-) There is definitely Na emission from  the dust tail in this one too. I think the third tail in Hale Bopp came from Na atoms from the coma which then behaved differently in the solar wind/radiation compared to the gas or dust and separated out into a third tail. 


Edited by robin_astro, 11 July 2020 - 09:56 AM.

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#8 happylimpet

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Posted 12 July 2020 - 01:22 PM

Robin this is a glorious and very cool result. I love the doppler shift relative to the telluric lines. Well done!

 

I'm planning on slinging an old diffraction grating over the front of a lens and seeing what I can get.....



#9 ButterFly

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Posted 12 July 2020 - 08:43 PM

I hope you've seen this lovely picture:

NEOWISE, double ion tails July 12



#10 robin_astro

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Posted 12 July 2020 - 09:04 PM

I hope you've seen this lovely picture:

NEOWISE, double ion tails July 12

Very interesting, particularly the difference in colour between the two gas tails. (If the brownish tail is a Sodium tail, it is not strictly an ion tail, unlike the blue green from the molecular ions, as the sodium atoms are neutral so behave differently in the solar radiation)

 

Robin



#11 ButterFly

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Posted 12 July 2020 - 09:14 PM

Very interesting.  The sodium lines are at about that color, but that red part is on the "wrong" side of the ion tail for neutral soidum.



#12 robin_astro

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Posted 13 July 2020 - 04:51 AM

Very interesting.  The sodium lines are at about that color, but that red part is on the "wrong" side of the ion tail for neutral soidum.

NH2 perhaps ?  eg as in this spectrum of C/2014 Q2  (Lovejoy) by Umberto Sollecchia for example. 

http://www.spectro-a...=6&t=1043#p4642

Does the ion tail direction depend on molecular weight,  the red NH2 being lighter than the blue green C2/CN ?  

 

Robin



#13 happylimpet

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Posted 13 July 2020 - 05:40 AM

Hi chaps,

 

I have a colour image from the 10th, and have made an RGB split; the red ion tail clearly has a very different structure to the blue/green components. Not as good as the image above it has to be said! This is NOT a final process - just a rough and ready to see whats there.

 

Red,green,blue:

 

Red_of_c2020f3neowise-20200710-1quicklinear lvls crop_bin_x8flatsubbed faff bin_lflat gamma_binstretch.jpg Green_of_c2020f3neowise-20200710-1quicklinear lvls crop_bin_x8flatsubbed faff bin_lflat gamma_binstretch.jpg Blue_of_c2020f3neowise-20200710-1quicklinear lvls crop_bin_x8flatsubbed faff bin_lflat gamma_binstretch.jpg

 

I had also assumed it was sodium - but interested in what it might be!

 

 

c2020f3neowise-20200710-1quicklinear lvls crop_bin_x8flatsubbed faff bin_lflat gamma2-qual90.jpg


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#14 ButterFly

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Posted 13 July 2020 - 06:03 AM

Carroll and Ostlie cite Mendis, Annu Rev Astron Astrophys, 26, 11, 1988.  The good stuff starts around pdf page 26, reference page 36. There is a rather complicated interaction with the solar wind and the Sun's magnetic field that was apparently not well understood in 1988.  There are a few cites that look interesting and more up to date.  It's a good starting point.  It could just be a mass spectrometer effect around the magnetic barrier separating out lighter ions.



#15 Octans

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Posted 13 July 2020 - 06:17 PM

It's almost certainly sodium. Enhances nicely with a sodium bandpass filter.

 

 

NH2 perhaps ?  eg as in this spectrum of C/2014 Q2  (Lovejoy) by Umberto Sollecchia for example.

    http://www.spectro-a...=6&t=1043#p4642

    Does the ion tail direction depend on molecular weight,  the red NH2 being lighter than the blue green C2/CN ? 

    Robin

It should not. All the ions behave almost as massless particles to the solar wind at this scale. Their motion is to spiral down the magnetic field lines, and the mass (and relative to charge and speed) dictates how wide that spiral is, but in general, that spiral motion is much too narrow too resolve anyways. There is a difference in how far away from the nucleus the ions are produced, but they should still spread out in a similar way and blend together since they're captured by the same magnetic field.

Also, the blue tail is mostly CO+ (not C2/CN, which are not ions). It probably also contains H2O+, NH4+, etc. blended in.


Edited by Octans, 13 July 2020 - 06:27 PM.


#16 robin_astro

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Posted 13 July 2020 - 08:30 PM

NEOWISE has now detected the sodium tail, contained within the broad dust tail so just seen as a narrower distribution of Na emission pointing in a slightly different direction.

 

https://psi.edu/news/neowisesodiumtail

 

I took a spectrum of a cross section through the tail tonight so it will be interesting to see if I can also pick this up

 

The reddish tail remains unexplained it seems

 

Cheers

Robin


Edited by robin_astro, 13 July 2020 - 08:34 PM.


#17 robin_astro

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Posted 13 July 2020 - 08:42 PM

NEOWISE has now detected the sodium tail, contained within the broad dust tail so just seen as a narrower distribution of Na emission pointing in a slightly different direction.

 

https://psi.edu/news/neowisesodiumtail

 

I took a spectrum of a cross section through the tail tonight so it will be interesting to see if I can also pick this up

 

The reddish tail remains unexplained it seems

 

 

Looking at the scale of the NEOWISE images, I see they are of the tail close to the coma  (within a few arcminutes) so perhaps the sodium tail splits from the dust tail further out giving the separate narrow orange tail seen in the images

 

Robin


Edited by robin_astro, 13 July 2020 - 08:42 PM.


#18 Octans

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Posted 13 July 2020 - 10:09 PM


 

The reddish tail remains unexplained it seems

The reddish tail is no more unexplained than the blue tail is. Appearance-wise, it matches with a neutral gas tail (like sodium). Color-wise, it matches with sodium. It clearly enhances through a 589 nm bandpass filter as sodium should. I only see a single red tail, so there's not really evidence for additional components to it. Until there's any evidence that it's not sodium, I don't see much of a mystery here.

EDIT: Curiously, this picture just appeared, purportedly showing a red feature in the tail with a sodium blocking filtering, suggesting there may indeed be more to it than just sodium (which definitely does still have a tail overlapping the ion tail): https://spaceweather...pload_id=165698 The mystery can now resume.


Edited by Octans, 14 July 2020 - 06:05 PM.

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#19 robin_astro

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Posted 15 July 2020 - 08:33 AM

Torsten Hansen has posted a slitless spectrum image on the Rspec forum which shows the sodium distribution relative to the dust.

https://groups.io/g/...se_and/75502060

 

There is a clear sodium tail diverging anticlockwise roughly in the direction of the gas tail (curiously the opposite direction to that seen in the PSI image) , though I have not tried overlaying it on a gas tail image to see where it lies

https://groups.io/g/...tachment/8091/0

 

 

Robin


Edited by robin_astro, 15 July 2020 - 08:53 AM.


#20 robin_astro

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Posted 15 July 2020 - 01:38 PM

There is a clear sodium tail diverging anticlockwise roughly in the direction of the gas tail (curiously the opposite direction to that seen in the PSI image)

 

 

Just checked with the PSI Team. The image on their website is indeed mirror flipped so the  direction of the gas tail and Torsten's and PSI's  sodium tails are all antilockwise relative to the dust tail

 

Robin



#21 robin_astro

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Posted 15 July 2020 - 07:50 PM

I have finally got round to  processing the high resolution spectrum. Results on my BAA website page

 

https://britastro.org/node/23284

 

The calculated velocities for the comet relative to the Sun and Earth are pleasingly close to the JPL Horizons figures for the time of the observation :-)

 

Cheers

Robin


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#22 mwr

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Posted 16 July 2020 - 04:25 AM

I have finally got round to  processing the high resolution spectrum. Results on my BAA website page

 

https://britastro.org/node/23284

 

The calculated velocities for the comet relative to the Sun and Earth are pleasingly close to the JPL Horizons figures for the time of the observation :-)

 

Cheers

Robin

Hi Robin,

 

that's beautiful astrophysics!

 

The Na D2/D1 line ratio for single resonance scattering in your near-nucleus spectrum is <2 and corresponds well to earlier observations of comet Hale-Bopp (https://orbi.uliege....ndle/2268/28972).

 

However, the sodium emission lines of the sky in your spectrum at the lower right corner (red line) are also of uneven intensity. In the raw spectrum which  I have created using V-Spec and your spectrum image this is not the case and they show even intensity (which should be the case for sodium atomic emission by collisional excitation). Could you please comment on this?

 

neo_hr.jpg



#23 robin_astro

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Posted 16 July 2020 - 06:58 AM

 

However, the sodium emission lines of the sky in your spectrum at the lower right corner (red line) are also of uneven intensity. In the raw spectrum which  I have created using V-Spec and your spectrum image this is not the case and they show even intensity (which should be the case for sodium atomic emission by collisional excitation). Could you please comment on this?

 

The spectrum  image has been non linear stretched to bring out the outer regions and the lines are very narrow so the maximum height will depend on the exact location relative to the bins so an measure of the integrated flux would be better (There is also a component from strong H2O telluric lines).

 

There does appear to be an inconsistency however between the relative intensities of the comet lines in the full spectrum of the inner coma (black line) compared with the inset showing the Na D lines which I need to check

 

Cheers

Robin



#24 robin_astro

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Posted 16 July 2020 - 08:20 AM

There does appear to be an inconsistency however between the relative intensities of the comet lines in the full spectrum of the inner coma (black line) compared with the inset showing the Na D lines which I need to check

 

OK the D2 comet line in the inset was partially saturated  which reduced the apparent D2/D1 ratio. (The inner coma spectrum in the main spectrum was from a shorter exposure and is correct.) This shows the correct relative intensities of the lines and the calculated integrated flux ratios in the outer coma.

 

_c2020f3neowise_incsky_365_20200710_995_telrem_annot.png

 

EDIT: The line subscripts are the wrong way round. The ratio is D2/D1  (D2 is the shorter wavelength)

 

Cheers

Robin


Edited by robin_astro, 16 July 2020 - 08:40 AM.

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#25 mwr

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Posted 16 July 2020 - 11:01 AM

OK the D2 comet line in the inset was partially saturated  which reduced the apparent D2/D1 ratio. (The inner coma spectrum in the main spectrum was from a shorter exposure and is correct.) This shows the correct relative intensities of the lines and the calculated integrated flux ratios in the outer coma.

 

attachicon.gif_c2020f3neowise_incsky_365_20200710_995_telrem_annot.png

 

EDIT: The line subscripts are the wrong way round. The ratio is D2/D1  (D2 is the shorter wavelength)

 

Cheers

Robin

Determining the D2/D1 line intensity ratio is one of the outstandig problems of the sodium behaviour in comets and the number of published quantitative estimates is small according to statements of  professional astronomers (https://link.springe...134/1.1819498).

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


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