Dust Obscured Spiral Galaxy in Cepheus

Uploaded 9/1/06

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Often portrayed in browns and yellows, this very highly obscured face on spiral requires special attention during processing to get the colors close to reality. In this part of the sky in Cepheus, the dust in the Milkyway not only obscures deep space galaxies and stars, but imparts a very strong yellow color cast as well. To remove the color cast and reveal the galaxy in its natural hues, a technique known to many professional day time photographers to remove color casts was used - Histogram Equalization. To do this, we use a mask to select only the galaxy and adjust the histograms to start and end in the same location for each of the three colors. Most notably, the blue histogram is strongly truncated on the top end, and must be brought back into sync with the others. A brown nearly monochrome galaxy is transformed almost by magic to a standard blue armed spiral, with a golden core and now visible for the first time - hordes of pink HII regions in the arms.

NGC6946 is only inclined 1 degree, and thus presents its face to us clearly. Listed at 9.6 magnitude, its large size of 12 arcminutes spreads out its light into a very faint disk, with little central condensation. The galaxy is listed as a SAB spiral and has as you would expect a very ruddy color index of .80, which is almost as red as a K type star. The faint galaxy to the lower right of the the main spiral is MAC 2033+6005, a 17th magnitude object with a size listed as .4 arcminutes. The field is devoid of any other faint galaxies because of the extreme dust in this region of the sky.

Additional Processing Notes:

An additional 2 hours of hydrogen alpha data was taken, and combined into the R channel at 100% with lighten, and the blue channel at 10% using lighten as well to maintain the proper pink coloration of Hydrogen. Extreme care was used to not white clip or oversaturate the hydrogen hues. The stars and galaxy remain close to G2V using this technique.

Instrument: 12.5" f/5 Home made Newtonian Platform: Astrophysics 1200 QMD CCD Camera: SBIG 10XME NABG with Enhanced Water Cooling Guider: SBIG ST4 Exposure: Ha^RGB = 120:40:40:40 RGB Combine Ratio: 1: 1.05: 1.11 Filters: AstroDon RGB Tricolor Location: Payson, Arizona Elevation: 5150 ft. Sky: Seeing FWHM = 5.5 arcsec (Maxim DL - 10min subframe), Transparency 7/10 Outside Temperature: 60 F CCD Temperature: -20 C Processing Tools: Maxim DL, Gralaks Sigma, Photoshop, PixInsight, Starizona Debloomer. HOME GALAXIES EMISSION NEBS REFLECTION NEBS COMETS GLOBULARS OPEN CLUST PLANETARIES LINKS


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