Schudel Family - Astronomy Log

Definitions

• Lights - Frames that include the subject matter.
  
• Offset/Bias frame - A calibration image taken with little to no exposure time.  Corrects for the noise inherent in the CCD.  Can be taken anytime and are considered viable for long periods of time.
  
• Dark frame - A calibration image taken with the same exposure time as the "Lights" frames.  Corrects for thermal and electro-luminescent noise that accumulates over long exposures.  Should be taken near to the same time as the lights so that temperature conditions are nearly identical.
• Flat frame - A calibration image taken of a uniformly bright, white screen.  Corrects for optical problems with the CCD and telescope.  Note that the focus point used on the subject must used when taking the flat frame.
• Cosmetic file - A file specific to IRIS that identifies hot, or warm, pixels on the CCD.  Derived from the dark frame.
  

Hints

• Take several (7-9) exposures of each of the calibration frames.  Then use IRIS to combine them.
• 2:1- lights to darks

GUI Procedures for IRIS

• Preprocessing->"Make an offset..." - Save the resulting master offset image.
  
• Preprocessing->"Make a dark..." - Save the resulting master dark image.
  
• Preprocessing->"Make a flat-field..." - Save the resulting master flat-field image.
• Load the master dark image and run "find_hot cosm X".  Vary X until 100-200 hot pixels are identified.  Result is in cosm.lst.
• Preprocessing->"Automatic preprocessing(1)..." or Preprocessing->"Automatic preprocessing(2)..."

CLI Procedures for IRIS

The above has been adapted from http://astro.ai-software.com/articles/dslr_iris/dslr_iris.html and http://www.saratogaskies.com/articles/cookbook/index.html

Info

• NGC4567 and NGC4568
• Siamese Twins or the Butterfly Galaxies

Original Imaging Info

• Images captured with the 0.81 meter telescope at TCO by Dr. Danford at 2010-04-16 at 02:30:37 (UT)
• 1024x1024 Apogee CCD
• Three 200 second exposures with "zip 5" filter

Image Post Processing - Method 2

• I used IRIS v5.58 to align/register the three images. It appears the RA/DEC was shifted slightly for each image.  This shift is apparent in "Method 1" as the true stars are slightly elongated.
• The three images were stacked with "add_mean".
• A crop was applied to remove the artificial border introduced by the registration.
• Then "skypoint/poly 3/synthe" to identify the circular gradient surrounding the two galaxies.
• The resulting gradient was removed from the image stack with "sub sky 500".
• The intensity levels were adjusted to be logarithmic and the result was exported with "saveppm".
• The exported Netpbm/PPM image was imported into GIMP.
• I further adjusted the black/white levels to contrast the galaxies against the background. 
• Then an aggressive removal of lone "hot-pixels".
• Followed by an aggressive application of the "Destripe" filter to remove the horizontal stripes.

Click image for a larger view.

Image Post Processing - Method 1

• I used IRIS v5.58 to stack the three images using the "add_mean" command. 
• Then "Remove Gradient (Polynomial Fit)" with medium/medium parameters.
• The resulting sky was removed from the image stack with "sub sky 500".
• The final FITS image was imported into GIMP where I adjusted the black/white levels to contrast the galaxies against the background.  Then removed lone "hot-pixels".

Click image for a larger view.

Ideas For Improvement

• The white speckles appear to be stuck pixels in the CCD.  There are also, less noticeably, stuck black pixels.  A light image, and a dark image, should identify the culprits and allow them to be removed prior to registration.  This may also help in removing the gradient.
• The horizontal stripes could further be eliminated with more images that vary the RA/DEC.

Here is a digital sky survey image of a slightly larger area.

Info

• Saturn

Original Imaging Info

• Images captured with the 0.81 meter telescope at TCO by Dr. Danford on 2010-04-17 at 03:34:33 (UT)
• 1024x1024 Apogee CCD
• Three 1/2 second exposures with "zip 5" filter

Image Post Processing

• I used IRIS v5.58 to stack the three images using the "add_mean" command. 
• The final FITS image was imported into GIMP where I adjusted the black/white levels and used the "Unsharp Mask" filter.