A New Telescope
I recently returned from having spent 2 weeks + 3 additional days at Obstech in Chile where I set up a new ASA600 RC telescope on a Planewave L600 mount.  If you haven't already seen the story of this telescope, you can see all the gory details here:  https://www.astrobin.com/8rstol/.  

Gathering the Data
Once I had the telescope ready for first light, I noticed that the Antenna Galaxies were well positioned in the sky to use as a test object.  These colliding galaxies have gobs of detail along with amazing colors so, this was a nice object for testing the system as I adjusted the telescope.  Over a period of about 21 days, I took over 1,000, 5 minute subs of this object.  The camera was pulled numerous times while I worked on aligning the optics so I had a lot of images taken at a variety of angles along with a lot of junk images.  Still a lot of the data that I gathered was some of the best I have ever seen.  The seeing during my visit was world-class (dipping under 1" for long stretches) and the best sub that I took with the red filter had a FWHM value of 0.88"!  One thing that I quickly learned with this telescope is that the use of the tube fans is essential for getting high image quality.  While I worked on the scope, I had it in the back of my mind that it would be amazing if I could actually get a fully processed image out of all this data and in the end, that turned out to be very doable.

When I sorted through what I had, I set an upper limit of just 1.35" FWHM to use for the image.  I was able to achieve that goal in all of the channels, except for the blue channel.  In that case, I only achieved a yield of just a little over 30 frames, which wasn't quite enough.  So, for the blue channel I opened up the limit to 1.45" FWHM, which yielded 67 subs.  All together, I was able to get slightly over 20 hours of high quality data to create this image.


Processing the Image
It is a real pleasure to work with such good data because almost everything gets easier.  Of course some things never change and with each run at the image, I'd spot some flaw that I didn't like and I'd have start over again to fix it.   This image is from my 3rd processing run.  I feel like a broken record to once again say that getting the color right provided some learning experiences.  I initially did a quick initial color check using SPCC on just an RGB combination and right out of the box, the colors looked absolutely spot on--almost perfectly matching the Hubble image of the same object.  So, I did a LRGB combination and again used SPCC on the result and...whoa, the colors were WAY off!  It produced a salmon pinkish + yellow washed out mess.  I had done a bit of preprocessing on the Lum data to reduce noise and reduce some very minor gradients and it clearly messed up the relative color balance across the field when I combined all four channels.  The interesting thing is that SPCC produced a very nice looking data plot that looked like it was doing the right thing.  I briefly considered doing what I had done with my Horsehead image where I combined the RGB data with the Lum-data in Photoshop but I rejected that idea to avoid converting to a 16 bit image too early in the processing.

So, in this case, I created a high quality, stretched RGB image that had been calibrated with SPCC.  Then I separately processed the Lum channel using MureDenoise and BXT.  I did a careful background "modalization" to eliminate minor gradients that were probably were caused by moonlight.  Next, I stretched the two images similarly and combined the result using the LRGBCombination tool in PI.  That did exactly what I expected it to do--just the same as applying a Luminosity layer to an RGB image in PS except that it produces a 32 bit image.  After I finished processing the LRGB image in PI, I finished it off with some final processing in PS, which is my normal SOP.

One thing of note is that the IMX455 sensor on the ASA600 is seriously over-sampled with a pixel scale of 0.18"/px.  In spite of that fact, with data this sharp, I could actually zoom in on the raw data until it became pixelated before I saw a loss in sharpness.  I had intended to simply down-sample this data to a 2x2 binned image, which increases SNR while doing nothing to the image sharpness.  Instead, I processed the full 1x1 image up to the end and as a last step, down-sampled the wide field image to a size that's a bit bigger than a 2x2 image.  It's not quite the right sampling, but I just liked the bigger image!  The main image of the core is a tight crop (about 4x) and it's shown at the native 0.18"/px, over-sampled rates so it is best viewed at very modest magnification.  Using two different sampling rates for these images prevented me from doing a wide-field mouse over and I didn't want to go backwards to fix it so you'll just have to check out the full wide field the hard way by clicking on it!  There's a lot going on in the core and it was tempting to compare this image with Hubble's but that's just not a fair fight so I gave up on that idea.  Still the details in the core are interesting to explore.

I debated about whether to make the wide field image or the core image the "main image", but I realized that almost all of the images of this object show the tails and very few have the advantage of a 4,200 mm focal length along with excellent seeing and sufficient optical resolution to go very far into the core so I chose the core image as the main image.  What do you think...tails or core?

A Little About the Objects
These two galaxies appear in the constellation Corvus at a visual magnitude of 11.2.  They are thought to be at a distance of about 45 Mly.   Around 1.2 billion years ago, the Antennae were two separate galaxies.  It is thought that NGC 4038 started out as a barred spiral and NGC 4039 was a spiral galaxy.  So, how do we know?  It turns out that these galaxies were used to develop computer models that could fairly accurately predict how galaxies interact in a collision.  The result of this modeling suggests that as these two galaxies passed through each other, stars and gas were released forming the long tidal streams known as the Antennae.  Modeling suggests that within another 400 million years, the nuclei of both galaxies will collide to eventually become a single core.  Models show that the overall shape will ultimately stabilize to become an elliptical galaxy.  It is fascinating to consider the scale and magnitude of this kind of collision.  Indeed, what would the sky look like from inside?

Comments and feedback are always welcome so feel free to tell me if I missed something.  Hopefully the brightness and contrast work as well on your monitor as it does on mine.

John