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Thursday, March 31, 2016

The Lower's nebula in visual colors



I have published a photo of the Lower's Nebula in mapped colors about a week ago. Now I'm publishing the same nebula as a visual natural color version.  Narrowband emission from hydrogen, oxygen and sulfur (H-a, O-III and S-II) are combined so, that the result is very close to a visual spectrum. Since the ionized hydrogen emits red light and it usually dominates nebulae, images are more or less red. Blueish hues are from ionized oxygen, O-III. Sulfur, S-II, emits red too and it get mixed to a hydrogen emission visually. 


Lower's Nebula
Click for a large image

 Image is in natural colors from the light emitted by an ionized elements, sulfur, hydrogen and oxygen.
The mapped color version of Lower's nebula can be seen HERE


INFO

The Sh2-261 (Sharpless 261), also known as the Lower's Nebula, is a faint region of doubly ionized hydrogen. Its apparent dimension is about 50 arcminutes in East-West direction and 30 arcminutes in North-South. So, it has an apparent size about twice the full Moon diameter. Of course the real size of the nebula is much larger! But we have no information about the distance of this hydrogen cloud, so we are not able to determine how large it is. (Source, www.skyfactory.org)

Technical details

Processing work flow

Image acquisition, MaxiDL v5.07.
Stacked and calibrated in CCDStack2.
Deconvolution with a CCDStack2 Positive Constraint, 21 iterations, added at 25% weight
Color combine in PS CS3
Levels and curves in PS CS3.

Imaging optics
Celestron Edge HD 1100 @ f7 with 0,7 focal reducer for Edge HD 1100 telescope

Mount
10-micron 1000

Cameras and filters
Imaging camera Apogee Alta U16 and Apogee seven slot filter wheel
Guider camera, Lodestar x2 and SXV-AOL

Astrodon filter, 5nm H-alpha
Astrodon filter, 3nm O-III
Astrodon filter, 3nm S-II

Exposure times
H-alpha, 9 x 1200s =3h
O-III, 3 x 1200s binned = 1h
S-II,  3 x 1200s binned = 1h
Total 5h


A single uncropped, calibrated and stretched 20 min. H-alpha frame as it comes from the camera





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