This is another image from the telescope live archives. The data supplied was very hard to work with – the dead CCD rows had some sort of glow that couldn’t be calibrated out, so I had to model the irregular glow on my own using DBE and then subtract it out. I’ve also been trying out the new DeepSNR noise reduction module for pixinsight which seems to remove chroma noise from RGB data quite efficiently. It’s pretty cool to look at the full-quality version of this image and see all the tiny background galaxies – I don’t think many of them are in the PGC catalogue, but most of them should be in one of the SDSS releases.
NGC 3981 is about 65 million light years from Earth, but even at that great distance it is considered a neighbour of our own galaxy, the Milky Way. The large stars in the image’s foreground are stars in the Milky Way. Because NGC 3981 is inclined towards Earth, astronomers are able to look right into the center of the galaxy. The bright center of the galaxy is dominated by a super-massive black hole (SMBH). The image shows the vast and delicate-looking spiral arms of the galaxy, which are star-forming regions full of dust. The disc itself is lit up with a host of hot young stars. Some of the spiral arm appears stretched out and misshapen, possibly due to an encounter with another galaxy at some time in the distant past.
Image:
Full-quality image here: https://live.staticflickr.com/65535/52721737493_27d3d76c8d_o.png
Annotated Image:
Full-quality image here: https://theastroenthusiast.com/wp-content/uploads/2023/03/NRG3981_annotated_Annotated.jpg
Details:
Telescope: ASA 1000
Camera: FLI PL 16803
Filters: Astrodon LRGB 2GEN
Location: El Sauce Observatory
Date of Observations: 2/29/2020, 3/4/2022, 4/21/2020, 4/22/2020, 4/27/2020, 4/28/2020, 4/29/2020, 4/30/2020, 6/19/2020, 6/20/2020
L: 33 x 1200s (11h)
R: 26 x 1200s (8h 40m)
G: 21 x 1200s (7 hr)
B: 25 x 1200s (8hr 20m)
Processing: Pixinsight
Credits: Data: Telescope Live; Processing: William OstlingProcessing:
Pre-processing and Stacking
- Linear defects from the CCD were modeled using image integration and DBE, then removed in pixelmath
- Images were cosmetic corrected for hot pixels
- The subframes were weighted, registered, normalized, integrated, and drizzled in WBPP
Preparation of all frames:
- Stacking artifacts were cropped
- RGB Channels were combined to create an RGB image
- RGB image was plate solved
- Starless DBE was applied to L, RGB as follows:
- Starnet 2 was applied to a clone of the target image, creating an image with stars and an image without stars
- DBE was applied on the starless image to create a background model
- The background model was subtracted from the stars image
- the RGB image was photometrically color calibrated and clipped H values were fixed with the repaired HSV separation script
Deconvolution of the luminance
- a PSF was created using the dynamic PSF process
- Linear starnet was applied to create a starless image and a star mask
- the linear image was duplicated, stretched, clipped, and convoluted to create a mask
- The starless image was deconvoluted using the RVC algorithm
- the stars were added back in
Linear noise reduction
- A low contrast mask was created and applied to the luminance image
- Noise Xterminator was applied with strength 73 and detail 0
- DeepSNR noise reduction was applied to RGB
Stretching
- A nucleus mask was created
- The luminance image was stretched using Histogram transformation using the nucleus mask
- The RGB image was using histogram transformation using the nucleus mask
Non-linear adjustments
- Saturation adjustments on RGB
- LRGB combindation
- Starless background fix
- Adam Block-style star reduction
- Background levels adjustment
- Saturation Adjustment
- Color adjustment
- Local Histogram Equalization
- Color Adjustment
- Background Set
- Slight histogram adjustment