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Monday, August 29, 2011

M16, the "Eagle nebula", reprocessed

Since my processing technique gets better and the time of year doesn't give any support, I have reprocessed some older images. There is now star colors added and other processing is tweaked too.

Merssier 16, in Serpens
Ra 18h 18m 48s Dec -13° 49′ 00″

M16, narrow band HST-palette and a broad band RGB-stars.
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This is a reprocessed closeup image of the "Eagle Nebula", M16, NGC6611, in constellation Serpens.
Messier 16 is a part of a diffuse H II emission nebula region, IC 4703 at distance of about 6.500 light years.
The region is under an active star formation. The tower of gas, seen middle Right in this image, is approximately 100 trillion km long. (60 trillion miles) The longest of the "pillars" is about seven light years long.
Tips of the pillars are "stellar nurseries", there are several, recently (~one million years ago) formed young stars.

Images are taken with the Northern Galactic group's remote telescope in Australia, from Oulu, Finland. .

Natural color composition from the emission of ionized elements, R=80%Hydrogen+20%Sulfur, G=100%Oxygen and B=85%Oxygen+15%Hydrogen to compensate otherwise missing H-beta emission. This composition is very close to a visual spectrum. Broad band RGB-stars.
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Technical details

16" RCOS ja Apogee U9000 camera. 
LRGB combo.
H-alpha 5x1200s, O-III 2x1200s, S-II 2x1200s . Dark and Flat calibrated.
Broad band luminance 15x300s.
RGB-colors Red 2x300s, Green 2x300s and Blue 2x300s.
Raw data is shared with Petri Kehusmaa and J-P Metsavainio

Processing workflow:
Image acquisition, MaxiDL
Stacked and calibrated in CCDStack.
Deconvolution with a CCDSharp, 30 iterations.
Levels, curves and color combine in PS CS3.

An experimental version of M16, narrow band colors with the broad band luminance.

HST-palette colors with a Broad band luminance and RGB-Stars.
Red=S-II, Green=H-a and Blue=O-III
Buy a photographic print from HERE

Natural color narrow band composition with a Broad band luminance and RGB-Stars.
Red=70%Ha+30%S-II, Green=O-III and Blue=70%O-III+30%H-alpha.
Buy a photographic print from HERE

In this experimental image, I have tested the method to use a clear filter luminance with a narrow band color. This is (only?*) scientifically correct method to use a luminance image with a narrow band colors, since the broad band luminance contains all the wave lengths used for color information.

I don't usually like to mix colors from a different imaging methods, like pure RGB and narrow band. In this case I have used RGB, real color, stars with an emission line image.
Some astro imagers tend to use H-alpha channel as a luminance, due the higher details and better S/N than any other channel has. Even though the visual appearance might look better, other channels, O-III and S-II, has no information in H-a luminance and all details in there are lost!

(*I have to point out, I use H-a  luminance with a many NB images but H-a is boosted with all the information in O-III and S-II channels used. I call this method "Tone Mapping". Step by step instructions can be found here: )

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