Schudel Family - Astronomy Log

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.