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Old 12-12-2018, 07:11 AM
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jsmoraes (Jorge)
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NGC 371 - Cluster and Nebula in SMC

Despite some images on internet show this nebula as red, my photo in 2011 using Color DSLR and this photo show the nebula as green.
Newtonian Reflector Telescope 305 mm F/5 - CMOS Mono Camera - LRGB Filters - Coma Corrector
RGB - 60 x 1 min
gain 174

And for green channel I processed with lowest scale value on Fits Liberator.

red - Arcsinh - scale 400
green - Arcsinh - scale 50
blue - Arcsinh(Acrcsinh(x)) - scale 100


DSLR image - 2011 - http://jsmastronomy.30143.n7.nabble....17-k9-crop.jpg

http://jsmastronomy.30143.n7.nabble....ide_091218.jpg

http://jsmastronomy.30143.n7.nabble....ail_091218.jpg


What visual color you get with this target ?

Last edited by jsmoraes; 14-12-2018 at 04:36 AM.
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Old 12-12-2018, 04:02 PM
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multiweb (Marc)
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I'm biased when it comes to green but looking at your starfield color I reckon you're on the money with your colors. The ony reason the other shot shows a red out line is probably because it is deeper.
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Old 13-12-2018, 08:20 AM
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Interesting result, Jorge.
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Old 14-12-2018, 12:00 AM
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Thank you for replies. I am asking about the color of the nebula because I know that green color isn't usual. At http://www.irida-observatory.org/Nam...346/NGC346.htm the nebula has a blueish color. It was used LRGBHa filters.

I have few information about the cluster and nebula.
The cluster has low metalicity. It has size of approximately 350 light years. It has an unusual number of variable stars, among these there are many slowly pulsating B stars.
About the nebula I only found information saying it is a H II region. For this information the color of nebula should be cyan. I read that Hydrogen has emission only on violet - 410nm, blue - 434 nm, cyan - 486 nm and red 656 nm


The green color can be from atmosphere action ? The target is very low on my field: maximum 40 degrees.
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Old 14-12-2018, 07:45 AM
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Atmos (Colin)
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I shot this about 12 months ago and found it was more of a teal colour so a mixture of green and blue. This would make it a strong OIII emitter with no Ha.
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Old 14-12-2018, 09:38 AM
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Quote:
Originally Posted by Atmos View Post
I shot this about 12 months ago and found it was more of a teal colour so a mixture of green and blue. This would make it a strong OIII emitter with no Ha.
Hi Colin, you referred to this as a strong emitter. This raises an interesting question about the conventional wisdom that says HA is emission and OIII is reflection. Is that a universal rule I wonder?

Peter
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Old 14-12-2018, 10:18 AM
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Atmos (Colin)
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There is a difference between OIII and reflection nebula. OIII is an emission line which has a teal colour whereas a reflection nebula is intrinsically blue when not obscured by dust.

A reflection nebula will not show up as a strong emission in an OIII filter.
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Old 15-12-2018, 05:20 AM
pmrid (Peter)
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Quote:
Originally Posted by Atmos View Post
There is a difference between OIII and reflection nebula. OIII is an emission line which has a teal colour whereas a reflection nebula is intrinsically blue when not obscured by dust.

A reflection nebula will not show up as a strong emission in an OIII filter.
Thanks Colin. I guess what I called "conventional wisdom" is neither. A quick trip to Google has sorted me out. And given me a good example - our old friend the Lagoon. It's a good day that starts with you not just older but wiser too.

Peter
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