NGC 7008, Nebuleuse du Foetus ; couleur ??

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NGC 7008, Nebuleuse du Foetus ; couleur ??

Postby etienne bertrand » Sat Jul 20, 2019 1:59 pm

Bonjour,

Cette nébuleuse est assez curieuse, ses couleurs sont bleues et violettes.
Savez vous pourquoi est elle colorée comme cela ? Quels sont les processus physiques ?

CI joint quelques photos et spectres.

Peux être un bon test pour Christian et le spectro UVEX, voir quelles raies d'émission et d'intensité elle a dans l'UV ?

Voilà les deux zones que j'ai prit pour faire les spectres
Image

Spectre de la partie gauche de l'image:
Image

Spectre de la partie droite de l'image :
Image

Le poster :
Image

Focus sur la zone violette :
Ci-joint la ou le spectre a été sélectionnée
Image

Le spectre : même si le continuum de l'étoile centrale n'est pas sélectionné et que l'emplacement de la zone sélectionnée est un peu plus éloignée on apperçoit un continuum sur le spectre..
Image
Last edited by etienne bertrand on Sun Jul 21, 2019 1:00 pm, edited 1 time in total.
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Re: NGC 7008, Nebuleuse du Foetus ; couleur ??

Postby etienne bertrand » Sat Jul 20, 2019 11:50 pm

D'où provient cette couleur violette ?
Normalement il y à plus du bleu-vert provenant de Hb et [OIII] et du rouge provenant de Ha, [NII] et [SII].
?
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Re: NGC 7008, Nebuleuse du Foetus ; couleur ??

Postby Hamish Barker » Sun Jul 21, 2019 6:19 am

can you make a plot of both on the same graph, and maybe also a plot of zone H minus zone B?
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Re: NGC 7008, Nebuleuse du Foetus ; couleur ??

Postby etienne bertrand » Sun Jul 21, 2019 2:07 pm

Hello Hamish,

I have made a new traitement on the purple zone, i think it's possible that the rays of 3800A to 4101A are responsable of this color :
Image

3426A : [Ne V] : ?
3444A : OIII : ?
3727A : [OII] : ?

3868A : [Ne III] : yes
3970A : H epsilon : yes
4101A : H dseta : yes


But possible an other physical phenomène in UV ?
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Re: NGC 7008, Nebuleuse du Foetus ; couleur ??

Postby Hamish Barker » Mon Jul 22, 2019 7:39 am

I am only a beginner in spectroscopy, and cannot confidently propose a hypothesis.

However, I do wonder what sort of colour camera was used in the colour wikipedia picture? Did it have any IR/UV cut filters, or if they had been removed, is it possible that the purple is in fact due to either IR or UV response outside the domain of the plotted spectra, where the colour response can get confusing.

I have noticed on my DSLR which has all filters in front of the sensor removed and replaced with fused silica for maximum transparency, that the far IR part of the spectrum shows in the colour camera pictures as a pink response, while the uv segment of spectra (only a little of it is visible, I guess the glass of the star analyser may be filtering it a bit) shows as a reddish-purple.

So it might be that the purple is in fact some IR response. maybe it's worth exploring that part of the spectrum of the nebula also, perhaps with a low-pass filter (eg. yellow or orange), to avoid 2nd order uv/purple/blue interference. perhaps then some other obvious emission line might be apparent.
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Re: NGC 7008, Nebuleuse du Foetus ; couleur ??

Postby Benjamin Mauclaire » Mon Jul 22, 2019 2:36 pm

Hello,

Filters used for the picture has to be known (bandwidth) in order to have a comparison with spectrum.
Therefore you will be able to find lines contribution for each color of the picture.
Although, astrophotographers often modify colors threshold with PS.
Anyway, purple=red+blue. But strong line here is green with [OIII].
So, Etienne, don't worry about that because there are no real answer if you don't have taken the picture yourself.

Benji
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