NGC 4631 - The Whale and the Hockey Stick (NGC 4656) - A second attempt, this time in LRGB-Ha…
March 24, 2021
Cosgrove’s Cosmos Catalog ➤#0067
The Whale (NGC 4631) and the Hockey Stick (NGC 4656) - in HALRGB. (click image for full resolution via Astrobin.com)
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About the Target
The Whale and the Hockeystick are two galaxies are found in the constellation Canes Venatici.
NGC 4631 is the larger and brighter of the two. Located about 30 Million Light years from Earth, this galaxy has a wedge-shaped form that resembles a whale, thus its name. NGC 4631 has a nearby dwarf elliptical galaxy, NGC 4627, as a companion. This is a rare example of a double galaxy and as such, has found its way into the Atlas of Peculiar Galaxies.
NGC 4656, the Hockey Stick - also known as the Crowbar Galaxy, is a highly warped barred spiral galaxy. Its distinctive shape is due to a *recent* gravitational interaction with NGC 4631. The "hook" of the galaxy is also listed as its own object, NGC 4657. Beyond the hook is a fuzzy patch which may be a dwarf elliptical galaxy that is merging with NGC 4656.
The Annotated Image
Annotated image of the Two Galaxies - done with Pixinsight ImageSolve and AnnotateImage Scripts.
The Location in the Sky
IAU/Sky & Telescope Constellation Map for Canes Venatici - The locations of the Whale & the Hockey stick is indicated with the yellow arrow.
About the Project
Now a few words about the capture and processing here. I absolutely love the control you have with a mono camera - and I certainly love the results that it can deliver - but it sure can generate a lot of data! I captured photons over 3 evenings and the capture and the calibration frames came to 19.1 GB of data! I then used the Pixinsight WBPP 2.0 script to calibrate and register the data and Image Integration to create the image masters. These processes created an additional 64 GB of interim data files. All of this boiling down, ultimately, to the jpeg you see here!
The LRGB captures were done with 120-second exposures and the narrowband Ha data was captured with 5-minute exposures.
During image processing, I created an LRGB image in the normal way, but then I extracted the Red channel and blended it with the Ha channel before folding it back into the image. The goal here was to make the bright and active Hydrogen-Alpha regions "pop" in the image - capturing detail that you just don't get with the Red filter alone.
I was fairly happy with the final result, but capturing this during a period with the moon out clearly costs me some of the subtle nebulosity in the outer regions - I worked hard to bring this out in the processing but there is only so much you can do. In Rochester, NY - you learn to take advantage of the clear nights when you get them!
I also wished I had done more Ha integration time - The Ha had a lot more noise than the other channels, and that complicated the processing…..
This was also the second time I shot this pair of galaxies. The first time can be seen HERE. Below is the image that came from that effort:
Previous Attempt
The was my first attempt taken in 2019 using an OSC camera (ASI294MC-Pro) and the Williams Optics 132mm FLT scope. (click to enlarge)
The current effort in LRGB-Ha. Taken with the ASI2600MM-Pro and the Astro-Physics 130mm Scope (click to enlarge)
This first effort from 2019 still does very well for itself. Having less than 2 hours of integration on an OSC camera - it still captures a lot of detail. The second image is greatly enhanced by the Ha data (IMHO).
Supernova in the Whale Galaxy (NGC 4631)?
Soon after posting this image, a member of the Astronomy Section of the Rochester Academy of Science, David Bishop, pointed out that was a potential supernova recently discovered in the Whale Galaxy. So I decided to process a cropped version of the Lum image to show what we had here.
More detail can be found HERE and HERE.
This is reported as a new transient source and has been labeled as "AT2021biy"
A "transient" basically means that it is a star or source of light that was not seen in previous image cycles. At this point, it could be a Nova, or a Supernova, or an LBV (Luminous Blue Variable Star - which often evolves into supernova). It was first discovered on Jan 29th of this year.
I thought it might be interesting to show - I was not aware of it when I captured the image. I last took an image of this galaxy back on June 15th of 2020, and no star is shown in the location in question.
More Information
Wikipedia Entry: NGC 4631 (The Whale)
Scie.News: Astronomers Spot Huge Magnetic Structures in ‘Whale Galaxy’
Wikimedia Commons: Hubble Mosaic Image of NGC 4631
The Sky Live: NGC 4631
Wikipedia Entry: NGC 4656 (THe Hockey Stick)
The Sky Live: NGC 4656
NASA: NGC 4656
Capture Details
Light Frames
The number of frames shown is after bad or questionable frames were culled.
45 x 120 seconds, bin 1x1 @ -15C, unity gain, ZWO Gen II R Filter
31 x 120 seconds, bin 1x1 @ -15C, unity gain, ZWO Gen II G Filter
38 x 120 seconds, bin 1x1 @ -15C, unity gain, ZWO Gen II B Filter
62 x 120 seconds, bin 1x1 @ -15C, unity gain, ZWO Gen II L Filter
r62 x 120 seconds, bin 1x1 @ -15C, unity gain, ZWO Gen II L Filter
16 x 300 seconds, bin 1x1 @ -15C, unity gain, Astronomiks 6nm Ha Filter
Total of 7.2 hours30 Dark exposures30 Dark exposures
Cal Frames
30 R Flat Darks
30 G Flat Darks
30 B Flat Darks
30 L Flat Darks
30 Ha Flat Darks30 R Flats
30 G Flats3
0 B Flats30 L Flats
30 Ha Flats
Capture Hardware
Scope: Astrophysics 130mm Starfire F/8.35 APO refractor
Guide Scope: Televue 76mm DoubletCamera: ZWO ASI1600mm-pro
Filter Wheel: ZWO EFW 31x8
Filters: ZWO LRGB Gen II filter set, & Astronomiks 6nm Narrowband filter set
Guide Camera: ZWO ASI290Mini
Main Focus Motor: Pegasus Astro Focus Cube 2
Guide Focus Motor: Pegasus Astro Focus Cube 2
Camera Rotator: Pegasus Astro Falcon
Mount: Ioptron CEM60
Polar Alignment: Polemaster camera
Software
Capture Software: PHD2 Guider, Sequence Generator Pro controller
Image Processing: Pixinsight, Photoshop - assisted by Coffee, extensive processing indecision and second-guessing, editor regret and much swearing…..
Why a focuser for the Guidescope?
Basically I am making this change to make the platform consistent with the WO132 platform. I would like to be able to focus the guidescope remotely under computer control. I would also like to have the ability to swap camera and use the TV76 as a wide field imager (using the AP130 as the guide scope.