Link to Redshift Chart
This is the first light image with my 12” f/4 Newtonian. At this point I was still using the SXVR-H694 camera, though.
Abell 1185 is a galaxy cluster centered around the large ellipticals NGC 3552 and NGC 3558, which are located about 450 million light years away at the southwest edge of Ursa Major. SIMBAD suggests the cluster has hundreds of members, and based on the SDSS9 redshift data, many of the brighter galaxies in this image are members. However, two of the most distinctive objects in this field of view (which is about 4 million light years wide at this range) do not appear to be cluster members.
The main attraction in this image, the interacting galaxy pair NGC 3561 and PGC 33992 (also cataloged as Arp 105) that form the large structure at left nicknamed the Guitar, are located about 395 million light years away (based on redshift measurements). That would place them well in front of Abell 1185 itself. These two galaxies appear to have collided at some point, producing a long tidal tail which stretches far to the north and also appears to wrap around NGC 3561, ending in the bright blue spot known as Ambartsumian’s Knot. The blue color of this tidal tail suggests that rapid star formation is occurring.
The large elliptical galaxy, NGC 3550, is located about 480 million light years away. This galaxy has an unusual triple core. The three cores appear to have very different velocities, suggesting they resulted from recent mergers.
Exposure: Total exposure time about 18.5 hours, 340:60:62:94 x 2 minutes LRGB. All bin 1x1. Data collected in March 2023.
Light pollution: SQM ~18.38 (Bortle 7-8, NELM at zenith about 4.5, Red/white zone border.)
Seeing: FWHM of integrated luminance 2.5 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/4
Scale of presentation: 0.9 arcsecs/pixel (75% of full scale).
Equipment:
Scope: 12” f/4 Newtonian with 3” Riccardi-Wynne coma corrector
Mount: Paramount MX+, connected via ASCOM Telescope Driver 6.2 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: SXVR-H694, connected via SX ASCOM driver 6.2.1.18212 (SX Windows Drivers 15.26.50.450 [i.e., version 1.2.2] also installed)
Filter wheel: Atik EFW2 with 7x1.25 carousel and Artemis 2.4.3.0 driver
Filters: Astrodon Type IIi LRGB
Focuser/Rotator: Moonlite Nitecrawler WR35
OAG: Orion Thin OAG
Guide cam: Lodestar (first generation). 4 second exposures
Automation SW: Sequence Generator Pro 4.2
Guide SW: PHD 2.6.11, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.6 SP1
Platesolving: ASTAP, failover to local Astrometry.net 0.19 server
Processing Software: Pixinisight, Photoshop CS2
Processing Workflow by Workspace in PixInsight 1.8.9:
1. Processing¬
RGB Combination for RGB frames
Calibration, weighting, registration and integration with WeightedBatchPreProcessing with flats and bias, using Cosmetic Correction with a master dark
Dynamic Background Extraction on luminance and RGB images
ImageSolve RGB, then run Spectrophotometric Color Calibration, using Average Spiral Galaxy white reference
Determine PSF using the PSFImage script, and enter this into BlurXTerminator
BlurXterminator using Correct First and manual PSF on luminance and RGB
NoiseXterminator on luminance and RGB
Canon Banding Reduction script
2. Luminance/Narrowband Stretching
Histo Trans x 3
Curves Trans
No denoise necessary
3. RGB Stretching
Create a saturation mask: apply ScreenTransferFunction to the stretched luminance, and then to Histo Trans. Clip the mask with Histo Trans and blur slightly with Convolution.
Histo Trans
Curves Trans to boost saturation, using the saturation mask to prevent spurious background colors from being boosted
Histo Trans
Curves Trans to brighten
Second application of Curves Trans to boost saturation, using the saturation mask
4. Color Blending
LRGB Combine
5. Background Subtraction (Artificial Flat)
To remove background lumpiness caused by heavy stretching due to my light polluted skies, I create and subtract an artificial flat, which is simply an image of the messy background, with all stars and imaging targets removed.
a. Create an image of the background by removing stars with StarXterminator
b. Clean this image up in Photoshop, removing the leftover galaxies and any leftover stars
c. Blur this background image slightly (otherwise in the next step you’ll remove all the noise, creating an unnatural-looking noiseless image)
d. Back in PI use PixelMath to subtract the background image from the main image (adding a pedestal, to avoid having a pure black background).
6. Final
Final Histogram Transformation
ICC Profile Transform to sRGB
Rescale as desired
ImageSolve
Create annotated images with the AnnotateImage script, using some custom databases to extract quasar redshifts and galaxy clusters
Save final image, annotated image, and inverted narrowband images (if any) as JPG
