Sh2-98 Emission Nebula (Colour)



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September 7, 2014

I am continuing my exploration of the Sharpless catalogue as summer transitions into autumn.  I haven’t seen a common name for Sh2-98.  I propose we christen it the Donut Nebula.

Sh2-98 is one of the fainter members of the Sharpless catalogue.  However, there is scant information that is readily about it, so I can’t tell you just how faint it is.  It is big, with half the Moon’s diameter in the sky.  The cosmic donut is a molecular cloud with about 3000 times the Sun’s mass, lying around 12,000 light years away.  Sh2-98 is lit up by the red star in the nebula, known as WR130.  WR130 is a Wolf-Rayet star and emits lots of energy that blows a bubble in the surrounding gas.  A more familiar example of this type of nebula is the Bubble Nebula.   As a bonus, little red planetary nebula Henize1-4 is near the right edge of the field, glowing at magnitude 10.5.  

This image is an example of what can be achieved even under a nearly full moon using narrowband filters.  The Ha data were acquired under a nearly full moon (the Ha image is here).  See my article on imaging in moonlight for more information.


Acquisition in Maxim DL.  All pre-processing and processing in PixInsight.  Acquired from my SkyShed in Guelph, ON.   SBIG STL-11000 with Baader HaRGB filters.  10″ ASA @ f/6.8 on a Paramount MX.  Guiding with SV-80 80 mm f/6 refractor and cameras Remote Guide Head.  Imaging runs were scripted using CCDCommander.   Moon near first quarter for RGB data and near full for H-alpha.  Transparency and seeing very good for R, G and B and excellent for H-alpha.

6x10m R, G and B; 23x20m Ha (total – 10hr40m)

The batch pre-processing script was used to calibrate, register and combine the frames.  R, G, B and Ha channels were cropped, R, G and B were combined, and RGB was background corrected with ABE.  Deconvolution was applied to the Ha channel, and the NB-RGB Combine script was used to combine the Ha and RGB data (Ha scale of 8).  The resulting HaRGB file was processed with HistogramTransformation, ACDNR (small scale), another HistogramTransformation, and ACDNR (large scale on only the darkest areas of the image).  The DarkStructureEnhance script was then applied with default settings except amount 0.25.  A slight curve was applied to the entire image and saturation increasedin the mid tones.  The image was then separated into large and small scales and multi scale processing applied to boost the nebula.  Image scale is 1.1 arcsec/pixel.


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