Hickson 88
Object: Hickson88, 4 galaxies in Aquarius.
Components, top to bottom:
- A: NGC 6978 Sb 13.3m 1.5'x0.7'
- B: NGC 6977 SB(r)a pec. 13.3m 1.3'x0.9'
- C: NGC 6976 SAB(r)bc 14m 1.3'x1.1'
- D: PGC 65612 Sc 14.8m 1.1'x0.2'.
Subimages: 23 frames x 600s (3.8 hrs) SD Mask combined after Bias and Dark calibration. 4
other frames were discarded due to changes in focus.
Scope: C11XLT with RLS65 reducer, EFL=1981mm (f/7 effective)
Mount: Losmandy G11 with Gemini L4
Camera: ST7EI (0.94"/pixel) set to -15C (first 15 frames) and -25C (last
8 frames)
Guiding: SX716 camera on a Taurus Tracker III OAG
Acquisition and Processing: MaxIm DL/CCD v4.5
Galaxy group imaged with over more than a month, 2006/08/16, 08/25, 08/30,
08/31 and 09/29. I started imaging at f/10 hoping to resolve the smaller galaxies
in this group. After three nights spread over two weeks I had weak results with
constantly poor seeing. Therefore I adding a focal reducer to the image
train and obtained the image above over two nights. Unfortunately the telescope
was now out of collimation making for some strangely shaped stars. These galaxies
are quite faint and small and would really require much more integration time
and good seeing to get a good image.
The above image was deconvolved with a diagonal kernel filter to remove the elongation
due to miscollimation, then it was deconvolved with a Gaussian kernel (which
essentially reproduces the Lucy-Richardson deconvolution routine). Finally
a gamma stretch was applied (DDP with no filter). Compare this result with
my previous attempts.
Below is an image from the data acquired at f/10. The image was deconvolved with LR, gamma stretched and then cropped to remove border effects from non overlapping subimages.
Subimages: 29 frames x 600s (4.8 hrs) SD Mask combined after full calibration. 26
other frames were discarded due to changes in focus, bad tracking or bad transpenrency.
Scope: C11XLT, EFL=2935mm (f/10.5 effective)
Mount: Losmandy G11 with Gemini L4
Camera: ST7EI (0.63"/pixel) set to -15C
Guiding: SX716 camera on a Taurus Tracker III OAG
Acquisition and Processing: MaxIm DL/CCD v4.5
Here is a direct comparison between the two images, the f/10 image on the right
has been rescaled and rotated to match the f/7 image on th left. Both have
been cropped to show the brightest three member galaxies.
In my opinion the f/10 image does contain a small amount of extra detail (e.g. near the core of NGC6976). However the lower resolution image seems to contain more faint details above the noise floor (e.g. spiral arms of NGC6976). I must conclude that when the seeing produces stars with FWHM>5.5 (3.5" at f/10) I am better off using a focal reducer to minimize read noise and gain field of view. Other objects I have imaged did respond to the extra resolution (see NGC6412 for example) but in those cases the FWHM<4 (2.8" at f/10).
