NGC 3718, NGC 3729 and Hickson 56 in Ursa Major
NGC 3718 is a warped spiral or lenticular galaxy about 52 million light years away. The distorted shape is likely due to an encounter with NGC 3729, which is about 150,000 light years away. The two nebulous objects just above NGC 3718 may also be remnants of that interaction, but though they’re listed in NASA’s Extragalactic Database they have no redshift estimates, so it’s not possible to be sure they’re at the same distance as the main galaxy. Hickson 56 is the bright cluster below 3718. The cluster is about 400 million light years away, and four of them appear to be interacting, with a cloud of matter surrounding them. Most of the other galaxies in the field are much farther away. The annotated image shows galaxies ranging from 1.1 to 4.1 billion light years, and a quasar at 10 billion light years.
Exposure: Total exposure time about 13.4 hours, 181:44:41:37 x 2 minutes LRGB. All bin 1x1. Data collected in December 2018 and January 2019.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: Average FWHM of subs around 2.5 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 1.2 arsecs/pixel (50% of full scale)
Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: Paramount MX+, connected via ASCOM Telescope Driver 6.1 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: SXVR-H694, connected via SX ASCOM driver 6.2.1.17140 (SX 1.2.2 also installed)
Filter wheel: Atik EFW2 with 7x1.25 carousel and Artemis 2.4.3.0 driver
Filters: Astrodon 5nm Ha/SII, 3nm OIII, Type IIe LRGB
Rotator: Optec Pyxis 2", connected via Andy Galasso's 0.4 driver (Optec Pyxis Rotator AG)
Focuser: Rigel Systems GCUSB nStep motor with driver version 6.0.7 on stock Celestron focuser
OAG: Orion Thin OAG
Guide cam: Lodestar (first generation). 4 second exposures
Automation SW: Sequence Generator Pro 3.0.0.8
Guide SW: PHD2.6.3, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.3.0.2831
Platesolving: PlateSolve 2, failover to local Astrometry.net 0.19 server
Collimation: Metaguide 3, using ASI120MM connected via ZWO Direct Show driver 3.0.0.2
Processing Workflow by Workspace in PixInsight 1.86
1. Calibration
BatchPreProcessing with flats, darks and bias, using Cosmetic Correction with master dark
Blink to preview and reject a few frames
Subframe Selector for luminance to confirm selections and weight by FWHM and SNR
StarAlign to register frames
2. Stack and Mure Denoise
Image Integration on each channel
Mure Denoise on each channel
RGB Combination for RGB frames
Dynamic Crop
3. Luminance Linear Processing
Dynamic Background Extraction
Deconvolution with Dynamic PSF and star mask for deringing support. Masked in using mask created in Photoshop.
4. Luminance Stretching
Histo Trans x 3
Curves Trans
Local Histogram Equalization on background, using mask, to enhance dust
TGV Denoise
Aggressive Multiscale Median Transform to remove lumpiness in background, using an inverted and blurred luminance frame as a mask to protect highlights
Local Histogram Equalization on galaxy cores
Mild Multiscale Linear Transform on dust lanes to enhance detail
Mild HDR Multiscale to enhance contrast
5. RGB Linear Processing
Dynamic Background Extraction
Photometric Color Calibration
6. RGB Stretching
Histo Trans x 3
Slight boost of saturation in galaxy with Curves Trans and luminance mask
7. Color Combination
LRGB Combination of luminance and RGB images
8. Star Reduction and Background Removal
Star masks for large stars
Morphological Transform to erode stars
Photoshop: Create an artificial flat by eliminating the remaining small stars with the Dust and Scratches filter
Subtract the artificial flat from the main image, masking out the galaxies
Use Radial Blur filter to obscure comatic blue halos on bright stars
Final aggressive Multiscale Median Transform to denoise background
9. Final
Final Histogram Transformation
Plate solve image with ImageSolver
Annotate image with script
sRGB on both images
Resample to 50% of scale
Save both images as JPGs
