Introduction – The objectNGC 1365 is also known as simply, “The Great Barred Spiral Galaxy.” It lies at a distance of about 56 MLy and it’s an enormous galaxy spanning a distance almost twice the size of the Milky Way. The morphological classification is (R')SBb(s)b and studies have revealed that it contains two bars. The large, long bar which visually stretches across the galactic core reveals an inner, smaller bar that is more easily visible in infrared images. The two bars are thought to be rotating at slightly different rates, creating the diagonal structures seen in the visible spectrum. Barred spiral galaxies are quite common and make up about two thirds of the total galactic population.
The two million solar mass supermassive black hole that lies at the heart of NGC 1365 has been the focus of intense study. In 2013, two X-ray space observatories, NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Space Agency's XMM-Newton teamed up to measure, for the first time, the spin rate of the super-massive black hole at the core of NGC 1365. The findings showed that it is spinning almost as fast as Einstein's theory of gravity will allow at nearly the speed of light. These findings resolved a long-standing debate about similar measurements in other black holes, leading to a better understanding of how black holes and galaxies evolve.
Taking the Data and Problems with the Scope NGC 1365 has an apparent size of 50” x 40”, an apparent magnitude of 10.3, and it’s loaded with interesting detail, which makes it a popular imaging target in the southern hemisphere. I started on this imaging project early in 2021 as the object was sinking out of sight. I restarted again this year as it cleared the horizon right around sunset in the Fall. Unfortunately, my remote scope has been riddled with problems starting last spring. That’s a part of the reason that there has been such a long gap since I posted my last image.
After replacing my failed ATIK Horizon 2 guide camera last February, the new one only lasted a few months before it too went “wonky” around mid-summer. The symptom was a sudden huge increase in dark current—at about 20,000 – 30,000 ADU. We tried new cables and fiddled with new drivers, cooling, and everything we could think of with no success. I settled into simply cooling the camera and subtracting darks. I still get a usable guide image but it has a VERY limited dynamic range of maybe 7-8 bits. Fortunately, I’ve got my original repaired Horizon 2 as a backup and I’m now reconfiguring the system to use a ZWO ASI1200 (uncooled), which are cheaper, smaller, lighter, and more reliable. Along the way, the observatory techs sent me a movie showing that the current guide camera has come a bit loose on its mount due to a loose threaded tightening ring. It’s not causing a guiding problem but it needs to be fixed. All that stuff is problem one.
The next problem hit late in the summer when my main QHY600M-P started to produce
very dark images. It appeared as if the camera was only transmitting 8-10 bits of the full 16-bit image. I asked the observatory techs to check the supply voltages and they were all normal. During the diagnostic session when we were cycling the power, the camera suddenly connected and started working normally. After that, I discovered that by cycling the power and/or rebooting the PC, I could get the camera to connect in a state that worked. Unfortunately, over a period of about two weeks, it became harder and harder to get things working. On a couple of occasions, it took 2-3 hours before I could get things connected and I had the feeling that at some point I wouldn’t get it going again. So, I finally addressed the problem by never turning anything off. That’s great--up until the next observatory wide power failure, but so far, so good.
I’ve asked QHY for some help to diagnose and repair the camera problem but they have been
totally unresponsive. Since they have me listed on some of their social media as one of their “imaging ambassadors”, I contacted their marketing person to see how to get help and she reassured me that someone would contact me. I waited a while and finally sent another direct request for help and never received anything back. That was about a month ago. So, you can now officially list me as EXTREMELY unimpressed with QHY service and responsiveness. I’ll work up a statement for them that they can post on their social media. In the meantime, I’ve ordered a C1x61000 Moravian camera to replace the QHY unit and I’m designing some adapters to mount it on my custom ONAG unit.
But wait, there’s more! Over this same time period, I noticed that my guiding data was consistently bad. At first, I chalked it up to bad seeing, which (believe it or not) does happen in Chile. However,
never having good guiding led me to wonder what in the world was going on. So, armed with a little advice from Gaston, I recalibrated the SKG guiding software and discovered that the calibration values were WAY off! The seeing on that night was spectacular and after calibration, I could see an immediate, huge improvement in my guiding numbers. The one niggling problem that remained is that after doing further testing, I learned that the mount could only go unguided for about 2 minutes before producing completely distorted stars (slightly ‘C’ shaped!) Before shipping the system to Chile, I could easily go at least 5 minutes unguided with perfectly round stars. I now notice that there appears to be a residual problem that produces correlated guide errors between the two axis along with consistently larger errors in RA. Planewave has quickly jumped in to review the mount parameters to try to identify a problem and they did a quick review of the mount tuning this afternoon. They ruled out any problems with cable tensioning through the mount, which can cause friction and a different response between the two axis. They also identified that something was loose on the mount back in February when the mount was last tuned (before the guide camera came loose.). They reset a couple of parameters and I'm going to give it a try before having the observatory techs secure the guide camera and look for anything else that's loose. This is still an ongoing investigation but I'm hopeful that we can get everything snugged down and the mount re-tuned.
I’m trying to get a new refractor configured to ship to Chile and I plan to head back down there early in the new year to deal with all of this stuff in person and to set up the new scope.
Processing the Data and SCC I wound up taking an enormous amount of data on this object (around 670 subs.) Normally, that allows selecting the very best subs while having enough data to beat down the noise. In this case, my data yield was around 17% in all of the channels with a FWHM limit at 1.9”. Frankly, that’s not very good. I got a few subs at around 1.4” FWHM but that’s above the ~1.1” FWHM numbers that @Kevin Morefield was getting with his new 17” CDK on the same night. That tells me that my system really needs a total (optics, mount, mechanics, software) tune up!
Since the PI team released the new Spectroscopic Color Calibration tool just as I started to process this data, I was really excited to try it. It takes a while to download all the catalog data but overall, the installation process is super simple. The operation of the tool is very similar to the PCC tool and since it takes into account the spectral response of the sensor and the filters, I had very high hopes that this is the ultimate solution for producing accurate colors. As usual, the implementation is really good but I discovered a few things that can affect the results.
In the case of this particular data set, the channels were really out of balance. That may have something to do with the problem with my main camera, which developed while I was gathering data for this image. Regardless, I quickly discovered that the fit for the B/G flux was quite poor as shown below.
By normalizing the channels to the G filter, I could get a MUCH better fit. I also discovered that the size of the minimum wavelet scale affected the stars that were fit, which makes total sense. However, it points out that some care is needed to get the best results out of this new tool. Here is how the fit looked after channel normalization. Note that the slope and white point vary significantly from the data above.
Once I had the data calibrated, I immediately noticed that the blue regions in the galaxy tended to show on my screen as more of an aqua rather than a blue-color. When I checked the histogram distribution, the green channel is definitely scaled to be stronger than the other two channels. (Here's the histogram AFTER, I reduced green by about 20% using SCNR.)
Maybe that’s correct, but the overall balance didn’t conform with my pre-conceived notion of where I wanted the colors to lie. So, I treated the SCC produced colors as a good starting point and tweaked things to look closer to where I wanted it to come out. I didn’t move the colors a lot, but this image doesn’t show what SCC produced. I’ll have to keep experimenting with it to learn more.
The biggest hurdle to processing this data were gradients! For some reason, every channel had a noticeable slightly diagonal gradient. It could have been due to some of the data being taken when the moon was up but I didn't seriously investigate that possibility. The subs looked clean but the gradient always showed up in the stacked data. I wound up finding that ABE was the most effective at removing the gradients in the linear stacked data. Starting with a gradient free LRGB raw image is critical to getting the colors--and pretty much everything else right in the final image.
As usual, feel free to provide feedback. I can always see all the flaws in my images so feedback helps me to better gauge where the limit of good-enough lies.
-John
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