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Old 07-03-2021, 12:49 PM
Paulyman (Paul)
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Asymmetry in the Great Nebula in Carina

So I gave a talk at our local astronomy group meeting the other night about narrowband palettes. One thing I showed was what happens when you create an SHO image from your narrowband masters versus what happens when you first linear fit your masters then create an SHO image.

I pointed out that the linear fit SHO image has far more complexity in terms of subtle hue transitions versus the typical blue gold duotone images you tend to get out of a straight SHO image with nuked greens.

The evidence I used to back that up was my current data of the Great Nebula in Carina. I showed an unfitted blue gold version and a linear fitted SHO version, which you see below. I pointed out the asymmetry left to right. Travelling right to left the tendrils of gas tend from red through orange to yellow. I have looked at other SHO images on Astrobin and it is present in them, so it isn’t a false gradient in my image.

I see it as an asymmetry between the H and S within the nebula hence the hue changes. I can’t find anything when I search the all powerful Google, does anyone know of any papers on this? It is fascinating to delve into what our images are saying to us.

Cheers,

Paul.
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  #2  
Old 07-03-2021, 12:56 PM
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multiweb (Marc)
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Beaute shot.

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Originally Posted by Paulyman View Post
I pointed out that the linear fit SHO image has far more complexity in terms of subtle hue transitions versus the typical blue gold duotone images you tend to get out of a straight SHO image with nuked greens.
Hear hear. Finally the voice of reason prevails over the lipstick renditions.

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Originally Posted by Paulyman View Post
I see it as an asymmetry between the H and S within the nebula hence the hue changes. I can’t find anything when I search the all powerful Google, does anyone know of any papers on this? It is fascinating to delve into what our images are saying to us.
MBJ probably can expand on this.

Also note the almost purple areas in the Oiii region. The same can be seen in the core of the rosette cluster in "un-nuked" renditions.
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Old 07-03-2021, 01:44 PM
Alchemy (Clive)
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I’m with Marc, give me a Rembrandt over a Warhol. Much prefer the play of light and shadow over pop art. However both sell for millions so go figure.

Dust lanes really pop out in this rendition. Space truly is dark and mysterious.
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Old 07-03-2021, 02:43 PM
Placidus (Mike and Trish)
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An exquisite image.

Last edited by Placidus; 07-03-2021 at 07:15 PM.
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Old 07-03-2021, 09:10 PM
Paulyman (Paul)
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Thanks all.

As a maths teacher, using a common mathematical technique to assist in my hobby is pretty cool. The advantage of linear fitting is two fold; firstly it is linear, as the name suggests, so it doesn’t change the underlying distribution within each master frame, it simply renormalises them to the weakest channel. Secondly it is deterministic, so I could give anyone my raw data and they could apply the same process and produce exactly the same fitted master frames. Or as kind of a 2a, I could take someone else’s data and apply the process to produce very similar master frames to my own.
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Old 08-03-2021, 09:56 PM
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Ryderscope (Rodney)
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A very worthy image Paul. The colour mapping allows for the display of the different elements very well and whilst still retaining the aesthetic appeal.
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Old 09-03-2021, 08:52 AM
Placidus (Mike and Trish)
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The H-alpha represents where the great bulk of the star-forming material is. (There can of course be far more hidden within dusty areas).

The OIII represents where there is hard (high energy per photon) UV light, typically from young, super-hot OB stars formed from the dust.

The OIII will not usually be exactly co-located with the H-alpha, because gravitational collapse to form the OIII stars is unstable, running away once started, and therefore localized rather than smooth and uniform.

Because of their very high mass and therefore very high temperatures, these stars do not live long - say a few million years as opposed to ten billion for the sun. They eventually explode as a type II supernova.

The supernova explosions regurgitate highly processed heavy elements from deep within the stars - sulphur and nitrogen being the most relevant here.

(Some very large, very heavy, very hot stars called Wolf-Rayet stars can liberate heavy elements from the core during their pre-supernova lifetime. Again this process is very localized and often very assymetric - see NGC 3199 in Carina).

The supernova explosions will be even more localized, and in beautiful examples like Gabriela Mistral, or just about anything in the Magellanic clouds (where star formation is proceeding with great speed and violence due to tidal disruption), you will see extremely localized SII structures as shock fronts and super-bubble structures around the sites of recent supernova explosions. The Chalice Nebula is an excellent example.

Later, as the supernova material gets more widely dispersed, these structures will be lost, but the SII will still mark out the broad areas of past supernova activity.

One final reason for asymmetry in very large structures, such as the area around the Statue of Liberty nebula: Galactic scale compression waves that form spiral arms move through a star-forming region, initiating star formation on one side before the other. H-alpha will be the first to appear, SII the last, and as the wave moves through, that will produce very large scale asymmetry.

Just a peek in the bookshelf for some relevant textbooks that discuss parts of the process.

Phillips: The physics of stars.
Bally and Reipurth: The birth of stars and planets.

Green and Jones: An introduction to the sun and stars.
Wheeler: Cosmic Catastrophes.
Kitchin: Galaxies in Turmoil
Percy: Understanding variable stars
Jones Lambourne Serjeant: Galaxies and Cosmology.

Hope that helps explain some of the mechanisms behind asymmetry of H-alpha, OIII, and SII distribution in star forming regions.


Best,
Mike

Last edited by Placidus; 09-03-2021 at 09:44 AM.
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Old 09-03-2021, 09:50 AM
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Quote:
Originally Posted by Placidus View Post
The H-alpha represents where the great bulk of the star-forming material is. (There can of course be far more hidden within dusty areas).

The OIII represents where there is hard (high energy per photon) UV light, typically from young, super-hot OB stars formed from the dust.

The OIII will not usually be exactly co-located with the H-alpha, because gravitational collapse to form the OIII stars is unstable, running away once started, and therefore localized rather than smooth and uniform.

Because of their very high mass and therefore very high temperatures, these stars do not live long - say a few million years as opposed to ten billion for the sun. They eventually explode as a type II supernova.

The supernova explosions regurgitate highly processed heavy elements from deep within the stars - sulphur and nitrogen being the most relevant here.

(Some very large, very heavy, very hot stars called Wolf-Rayet stars can liberate heavy elements from the core during their pre-supernova lifetime. Again this process is very localized and often very assymetric - see NGC 3199 in Carina).

The supernova explosions will be even more localized, and in beautiful examples like Gabriela Mistral, or just about anything in the Magellanic clouds (where star formation is proceeding with great speed and violence due to tidal disruption), you will see extremely localized SII structures as shock fronts and super-bubble structures around the sites of recent supernova explosions. The Chalice Nebula is an excellent example.

Later, as the supernova material gets more widely dispersed, these structures will be lost, but the SII will still mark out the broad areas of past supernova activity.

One final reason for asymmetry in very large structures, such as the area around the Statue of Liberty nebula: Galactic scale compression waves that form spiral arms move through a star-forming region, initiating star formation on one side before the other. H-alpha will be the first to appear, SII the last, and as the wave moves through, that will produce very large scale asymmetry.

Just a peek in the bookshelf for some relevant textbooks that discuss parts of the process.

Phillips: The physics of stars.
Bally and Reipurth: The birth of stars and planets.

Green and Jones: An introduction to the sun and stars.
Wheeler: Cosmic Catastrophes.
Kitchin: Galaxies in Turmoil
Percy: Understanding variable stars
Jones Lambourne Serjeant: Galaxies and Cosmology.

Hope that helps explain some of the mechanisms behind asymmetry of H-alpha, OIII, and SII distribution in star forming regions.


Best,
Mike
Great post mate about the physical processes responsible for the distribution of materials in nebulae and a great reminder about why spatial arrangement of colours and details matter in what we're imaging.
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Old 09-03-2021, 09:52 AM
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vlazg (George)
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Paul, this is a fantastic image, I keep coming back to look at it. It does not have to be tricked up out of all proportion to stand out. Definitely not a “ kardashian”
And there are stars.
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Old 09-03-2021, 05:51 PM
Paulyman (Paul)
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Quote:
Originally Posted by Placidus View Post
The H-alpha represents where the great bulk of the star-forming material is. (There can of course be far more hidden within dusty areas).

The OIII represents where there is hard (high energy per photon) UV light, typically from young, super-hot OB stars formed from the dust.

The OIII will not usually be exactly co-located with the H-alpha, because gravitational collapse to form the OIII stars is unstable, running away once started, and therefore localized rather than smooth and uniform.

Because of their very high mass and therefore very high temperatures, these stars do not live long - say a few million years as opposed to ten billion for the sun. They eventually explode as a type II supernova.

The supernova explosions regurgitate highly processed heavy elements from deep within the stars - sulphur and nitrogen being the most relevant here.

(Some very large, very heavy, very hot stars called Wolf-Rayet stars can liberate heavy elements from the core during their pre-supernova lifetime. Again this process is very localized and often very assymetric - see NGC 3199 in Carina).

The supernova explosions will be even more localized, and in beautiful examples like Gabriela Mistral, or just about anything in the Magellanic clouds (where star formation is proceeding with great speed and violence due to tidal disruption), you will see extremely localized SII structures as shock fronts and super-bubble structures around the sites of recent supernova explosions. The Chalice Nebula is an excellent example.

Later, as the supernova material gets more widely dispersed, these structures will be lost, but the SII will still mark out the broad areas of past supernova activity.

One final reason for asymmetry in very large structures, such as the area around the Statue of Liberty nebula: Galactic scale compression waves that form spiral arms move through a star-forming region, initiating star formation on one side before the other. H-alpha will be the first to appear, SII the last, and as the wave moves through, that will produce very large scale asymmetry.

Just a peek in the bookshelf for some relevant textbooks that discuss parts of the process.

Phillips: The physics of stars.
Bally and Reipurth: The birth of stars and planets.

Green and Jones: An introduction to the sun and stars.
Wheeler: Cosmic Catastrophes.
Kitchin: Galaxies in Turmoil
Percy: Understanding variable stars
Jones Lambourne Serjeant: Galaxies and Cosmology.

Hope that helps explain some of the mechanisms behind asymmetry of H-alpha, OIII, and SII distribution in star forming regions.


Best,
Mike
An absolutely stellar (pun very much intended) post. A wealth of information here. I had not at all considered that the asymmetry could possibly come from galactic scale phenomena.
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Old 09-03-2021, 05:52 PM
Paulyman (Paul)
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Originally Posted by vlazg View Post
Paul, this is a fantastic image, I keep coming back to look at it. It does not have to be tricked up out of all proportion to stand out. Definitely not a “ kardashian”
And there are stars.
Thanks mate. I am starting to realise a less is more approach is my thing.
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Old 09-03-2021, 08:35 PM
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multiweb (Marc)
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Thanks mate. I am starting to realise a less is more approach is my thing.
Good data requires very little processing.
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