NGC 1499 (California Nebula)

NGC 1499
All Images Copyright Steve Cannistra

Please click here for a 45% size image.
Please click here for a 65% size image.

Magnitude:  ?
Size: 1 x 4 degrees
2.6 x 3.9 degrees
Distance: 1140 light years
RA (Jnow): 4h 01m 35s
Dec (Jnow): +36 degrees 25' 52"
Position Angle: minus 2 degrees

This is a 7.5 hour exposure of NGC 1499, a large hydrogen emission nebula in Perseus.  NGC 1499 is one of a few nebulae that emit strongly in both H alpha (red) and H beta (blue), with little OIII emission, skewing the usual red color typical of emission nebulae towards the blue.  The star responsible for exciting hydrogen emission from the nebula is thought to be Xi Persei, a "runaway star" that is described on Rob Gendler's website.  Feel free to check out the larger size images above, as well as my H alpha image used as part of this color composite. 

Photographic Details:

Dates:  September 16 and 20, 2007: Ha;  September 17 and 18: RGB.
Scope:  Takahashi FSQ106 at f5 on the Takahashi NJP Mount.
Autoguider:  SBIG ST-402 with e-finder.
Camera:  STL11K -20C.

Astronomiks LRGB set (50mm unmounted); Baader 7nm Ha filter (50mm unmounted).
Exposures:  Ha- 12 x 20'; Red- 10 x 6'; Green- 12 x 5'; Blue- 11 x 8'.  Total exposure 7.5 hours.
Conditions:  Temperature was generally cool 55-60 degrees F average.  Transparency varied, and several nights of exposure were need to obtain the very best frames for processing.
Post-processing:  Calibrated, aligned, and Sigma Clip combined in Maxim, followed by DDP in ImagesPlus (IP).  Further processing in Photoshop CS (16 bit format).  The RGB was constructed as usual.  I then quantitated the color of the nebula in PS using the color sampler (eyedropper) tool, noting the relative proportions of R, G, and B.  The Ha signal was then added to the RGB in the following proportions (lighten mode), in order to preserve the color balance determined by the eyedropper tool:  Ha-Red, 50%; Ha-Green, 7%; Ha-Blue, 15%.  In this way, the colors remained "true" to the original RGB while at the same time allowing the Ha to enhance color and detail.  This enhanced "RGB" image was then used to provide the color, with Ha used as luminance (i.e., Ha"RGB").

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