neilfleming
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Registered: November 2006
Location: Boston
Posts: 246
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IC443 - The "Jellyfish" Nebula
This is a photo of IC443, a “supernova remnant” (SNR) located in the constellation Gemini. It is commonly known as the “Jellyfish Nebula”, and is considered to be one of the highlights of the winter astro season.
These types of objects are created by one of the most important processes in the universe - a supernova event - when a star explodes and scatters the heavier chemical elements it has synthesized during its lifetime back into space. This material will eventually coalesce into future stars and planetary systems.
IC443 is thought to have been formed between 30,000 and 35,000 years ago, and most likely is the remains of the pulsar, G189.6+3.3. Located about 5,000 light years away, the pulsar’s X-ray emissions excite the material of the nebula, causing the chemical components to emit light in their characteristic wavelengths. Additionally, the expanding bubble of gas continues to plow through the interstellar medium (ISM), which are latent clouds of gas in our galaxy), and further glow is added due to this interaction.
This nebula is comprised of hydrogen, oxygen, silicon, carbon, and iron, which were created through the nuclear fusion process during the predecessor star’s lifetime. Photographically, it is strong in both Ha and SII light, so our narrowband filters pick this up well.
The two bright stars are Eta (Propus) and Mu Geminorum (Tejat). Under RGB imaging, Tejat is noticeably reddish in color, illustrating its cool 3650 Kelvin degree surface and class M3 status. Lying 230 light years away (less than half the distance of Propus), Tejat is a red giant that radiates about 1540 times more energy than the Sun. The low temperature leads to a star of tremendous size, one that is actually large and close enough for an accurate measure of its angular size, 0.0135 seconds of arc. Tejat therefore has a radius 104 times that of the Sun, or 0.48 Astronomical Units, about half the size of the Earth's orbit.
Dates Taken:
- 11/18/2006 through 3/1/2007
Equipment Used:
- TMB 203 F/7
- SBIG STL-6303
- Paramount ME
- FLI PDF
- Astrodon 50mm Ha, with 6nmm bandpass
Exposures:
- TMB: 16x30 minute subs plus 29x5 minute subs, totaling 10 hours, 25 minutes
Processing:
This image is from the the TMB 203 F/7 (1421mm).
An interesting attribute of this series of images is that virtually all of the bloom removal was done in CCDStack. This was done by processing the 5-minute subs ahead of the 30-minute subs. I first produced a “5-minute sub master”, via a SUM combine. Then, while processing the 30-minute subs, I made the blooms “transparent”, then incorporated the 5-minute sub master in the stack to allow for the real data to poke through.
Workflow:
CCDStack:
Process the short, 5-minute, Ha data:
1) Calibration with darks, flats, and bias frames
2) Bloom rejection
3) Impute (minor) bloomed pixels
4) Rotate all subs to the same object orientation
5) Image registration (bilinear)
6) Normalization (Auto)
7) Data rejection (Poisson sigma)
8) SUM combine. The SUM combine is required so that this “mini-master” can be used to present data underlying the blooms from the longer-duration subs later in the process
Process the longer, 30-minute, Ha data:
1) Calibration with darks, flats, and bias frames
2) Bloom rejection
3) Set bloomed pixels to, “MissingVal”, so that they are, in effect, “transparent”
4) Rotate all subs to the same object orientation
5) Load in the prior “mini-master” of the SUM combine of the 5-minute data
6) Image registration, to the “mini-master” as the reference image (bilinear)
7) Normalization (Auto)
8) Data rejection (Poisson sigma)
9) Mean combine the achieve the final result
10) Deconvolution, Positive Constraint, 20 iterations
11) Save as a scaled TIF for importing to Photoshop
Photoshop CS2:
- Noise removal (NeatImage)
- Shadow-highlight to bring up the background data, tone down the highlights
- Noel Carboni’s Photoshop action for “local contrast enhancement”
- Overall “contrast curve”
- Multi-layer High Pass filtering at differing pixel radii
- Sharpening
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