NGC 1514
Object: NGC 1514 planetary nebula in Taurus, 10.9m, 2.2' D with 9.4m star in center.
From the Monthly Notices of the Royal Astronomical Society, Vol. 74, p.234 published
01/1914:
The nebula H.I.V. 69 Tauri (h 211, N.G.C. 1514, G.C. 810), the first planetary nebula
discovered, was described by Sir William Hershel in November 1790 as "a most singular
phenomenon : a star 8th magnitude with a faint luminous atmosphere of a circular
form, about 3' in diameter. The star is perfectly in the center, and the atmosphere
is so diluted, faint and equal throughout, that there can be no surmise of its consisting
of stars, nor can there be a doubt of the evident connection between the atmosphere
and the star."
Subimages: L: 100 x 100s (2.8 hrs), RGB: 10 x 100s (<0.3 hrs each) SD Mask combined
after bias and dark calibration. Output FWHM~2.7"
Scope: C11XLT with EFL=2970mm (f/10.6 effective)
Mount: Losmandy G11 with Gemini L4
Camera: ST8XME (0.62"/pixel) set to -40C (N down, E right)
Guiding: SX716 camera on a Taurus Tracker III OAG. Exposure time 1 sec, dithered.
Acquisition and Processing: MaxIm DL/CCD v4.5
Imaged on: Dec 20-21, 2006 (first LRGB image!)
Processed on: Jan 2, 2008
Processing for LRGB frames unless noted:
Combine: SD Mask, Align=Auto star match, Bicubic resampling.
Filtered with Kernel LowPassMore (RGB frames only)
Flatten Background
Aligned to L
Crop to 300,40-900,900
Equalized bgd to 100 with pixel math for color planes and L frame. Pre equalize
bgd levels were: L=202.6 R=121.55 G=136.1 B=108.4
Combine Color in Lab space with Lweight=100 %, AutoBgd=true and ratios R=1:G=1.02:B=1.26
Split tricolor, reset bgd levels to 100 ADU with pixel math R=+0.64, G=-0.24 and
B=+1.55, and reassembled color image with Color Stack command.
Stretched to 8bit
Kernel filter Average 7x7 with range restriction 0-60, ReduceRadius=3 and FeatherDist=10
Kernel filter LowPassMore with range restriction 0-150, ReduceRadius=3 and FeatherDist=3
Cleaned color splotches, arc reflection and bad column with clone tool
Resized from 900x900 to 600x600
Original processing Jan 2007
Processing:
Combine: SD Mask, Frame Align=Auto star match, Bicubic resampling.
Filter: Kernel LowPassMore
Flatten Background
Color combine: R=1:G=1.1:B=1.4
Levels (on an 16bit FITS file where the brightest star tops out at 16K counts!):
|
|
Black |
Gamma |
White |
|
R |
6 |
1 |
26 |
|
G |
7 |
1 |
26 |
|
B |
6 |
0.95 |
26 |
Half Size: Hides imperfections!!!
Since I haven't been able to calibrate on a G2V star yet the color ratios and levels are a best guess. The color data was acquired without a filter wheel, I removed the camera and screwed the filter into place for each filter, what a pain in sub zero weather! Therefore I have very little color data. Artifacts are present from driving the TEC too hard (vertical banding) and some kind of USB contention between the SX716 and ST8XME (vertical line right of middle), unplugging the SX camera makes it go away, certainly at first I was quite panicky that the problem was in the brand new KAF1603 sensor!!! These artifacts are mirrored left-right due to imaging on both sides of the meridian. Dust spots also remain since I didn't take any flats.
One Year Later...
January 2nd, 2008.
Having acquired a G2V star calibration and much more experience I have started to reprocess the original data! The background level of the individual RGB and L frames was manually equalized to 100 ADU by inspecting the bgd level with the MaxIm Information window and using the Pixel Math command Add Constant feature. The left panel is the output from an LRGB combine of those equalized frames with the following settings: Lab combine space, L weight = 100%, Auto Bgd Equalize = On and RGB ratios 1 : 1.02 : 1.26. The proper background balance was affected by the Color Combine algorithm since the Auto Bgd Equalize was turned on. When using non-unity combine ratios this switch must be turned on otherwise the different ratios will skew the bgd level themselves, but the automatic setting doesn't always pick the correct bgd values. Sorta catch22!
The right panel is screen stretched to exactly the same background and range as the left panel (black level = 97, white level=120, nebula avg~108, center star peak value~16K ADU) but is the result of tweaking the individual RGB background levels again. To do this I split the LRGB image using the Split Tricolor command, again inspected the bgd with the Information window and used the Pixel Math command to change the levels by R=+0.64, G=-0.24 and B=+1.55 to reset them all to 100 ADU (typical bgd standard deviation was ~0.7 ADU). Then the color image was reassembled using the color stack command which inserts three mono image buffers into a color image buffer.
Some cosmetic cleanup and non-linear stretch is still required, however the nebula color is as true as I can make it.