Globular beauty animated

The usual full moon drill

When it’s getting close to the full moon, the typical dilemma rises up: which subject are we going to slightly disrespect?
Yes, because we are basically saying: “Well, dear sky, we need something it’s not so fancy to image with a new moon, but also, we hate not to shoot something if the weather allows it. Too many cloudy nights in our past to not try something!". And so, the research begins based on a few simple principles: as far as possible from the moon, higher than 30° and… most likely a cluster. Which doesn’t leave many choices in a period close to full moon.

This time the victim was selected to be NGC 3201.

The usual drill starts. Since we are relatively new with this telescope, we decided to do some test on the length of the exposure for the stars - 30 sec, 60, 120, 180, 300 – to see how the integrations look like. The weather was really good and so we are able to gather 3-4 nights from the late afternoon to the moment the cluster drops below the 30°. However, the invasive moon phase is lasting longer than that and so we go with the usual side-dish to accompany a cluster: hydrogen alpha. Some nebulosity is always nice and add some fanciness to the picture. Will there be any?

Well, probably if you’ve seen the picture, you know the answer but the road to reach the final result was long.

A hint of something more

It all started as we noticed that there was an area, arc shaped, that was slightly whitish, more than the rest of the picture. It was also true that the number of stars and the arrangement of the most luminous ones could have impacted the background with their halos. But the gut feeling was there: this could be something interesting. And so, we continued.

After gathering 8-9 hours of Ha with frames of 600 and 900 seconds, we tried a quick and dirty integration. There were indeed some very interesting areas: first two distinct arches, just passing through the cluster, and some concentric signal there were the background looked to be lighter; and second a “three thin vertexes” signal not too far away from the cluster. Many other “fluffs” were just galaxies, as we compared the frame to the data and catalogs on Aladin. The shapes within the Ha signal were too interesting to just stop there, but the moon is still there to allow shooting oxygen. Maybe is not so popular… but we opted to have some sulfur time!

The sulfur signal also showed very similar results to the H-alpha.

The balance between excitement and sanity

The chats between me and Alex were getting sillier and sillier: from moments of pure excitement to tactical pessimism to not jynx it. At this point we tried to get a bit more educated about the situation in this area of the sky. We are far away from being experts, so we tried to look on Astrobin and other places for information related to this area. We also used ChatGPT to help us find any paper or similar related to this cluster but nothing helpful was found.

On Aladin, on the quest for deeper research, we could clearly see that there is H-alpha signal on the side we were seeing the arches, so that could have been the signal we were getting.

In the image below you can see the look according to the Finkbeiner Ha database in Aladdin. The first image represent the same FOV of our frame. The second is a wider field of view. The cluster is where the purple pointer is.

In the image above you can see that we are in the limit of Vela, close to Antlia, where there is still quite some Ha signal.

In the Galex database an interesting arc is also present, which sort of matches the data we got. We were not sure if was an artifact or not, but it fueled the interest. See the image below.

The moon sets, OIII game is on

As the Moon started rising later in the night, we took the opportunity to grab some OIII frames in the first part of the session.

We captured 8 * 900s frames, quick integration, and… yes! Not very strong, but two main weak lines appeared, matching the Ha and SII structures. There was also something else which was also nice to see.

The excitement built up. We contacted a few friends for some additional opinions. We continued gathering data (the weather was just so good for such a long period, it was unbelievable). We did some more test based on the suggestions (and some more studying on Pixinsight techniques) to exclude that the signal is real and not some silly artifact or miscalibration result. We redid the stacking 3 or 4 times with slight changes, but the results were consistent; good sign!

We gathered more and more data, even in a 4 panel array to see how the signal was continuing outside of the initial frame, however this was going to be to take too many days considering that the time available on the target was getting shorter and shorter. There were hints of additional signal.
Below are the roughly aligned panels with 2 hours each of oxygen data:

At that point we made the decisions to just focus on the original panel. While it would have been extremely interesting and cool to try to assess completely the extension of the signal, it was also quite impractical to gather some decent integration time on each of them.

Additional detail to be noted.

At the end we gathered around 70 hours on the various filters, and apart from the most evident topic of the discussion, we found other interesting details in this image that caught our attention.

A "three-blade boomerang" shaped signal.
Since the very beginning it appeared in the first Ha integrated frames.

Here is what it looks like in the sulfur frames

And here the SHO-RGB final detail:

Pixel peeping the image

While exploring every pixel of the image, we've noticed some interesting colored details.
The RGB image was color calibrated with Spectrophotometric Color Calibration, with all the setting of the camera and the filters.
By both selecting "Average Spiral Galaxy" and "G0V" stars, which should be the standard way to go with these processes, the color of the objects listed before were still extremely evident.

We checked on Aladin Sky Atlas and every faint galaxy was of course there well catalogued.
We have found a series of stars with striking hues in cyan and deep orange which made completely sense to the type of stars they were.
Below are those are the most interesting.

Purple star Halo within the cluster:
This one is very interesting: it's the only one with a clear purple halo and questioning ChatGPT provided some possible explanation that could make sense for the type of star it is (RRLyrae). It's literally the only star with this halo at looks like cromatic aberration but it doesn't make much sense that's the only one in the whole frame. Watching different other images and catalog also has shown that indeed the color of this star looks different in other sources as well.

Active galactic nucleus candidate (AGN)

A note on the gear and the location

Throughout this project, one thing became increasingly clear: the DeltaRho 350 is a damn good telescope.
It's now almost a year that has been in action, unfortunately our jobs didn't leave the chance yet to showcase too much of this beast.
Even more striking was the color accuracy in RGB imaging. After proper calibration, we could see rich, natural-looking hues that brought out subtle differences.

And we can't forget on how good the sky is at the Springbrook observatory.

Special Thanks

A special thank goes to Paul, who is taking care of the scope there at site and is always patient and helpful to make sure that the rig runs to its fullest.

A final consideration

Is there truly a new discovery? Maybe. Probably not.

But what we can say is this: whatever we've captured around NGC 3201 hasn’t been widely imaged or showcased before. The result feels surely unique.
We've followed up on our curiosity in the boredom of a full moon, frame by frame, night after night.
We've got exposed and learned more about databases, stars type thanks to the support of more knowleadgeable people. And that's already enough to us.

Just yesterday we found this on SHS, inspired by a comment from a fellow astrophotographer on the forum
I'll add also a check from just yesterday, inspired by a comment on a forum we went to check also the SHS (hydrogen database). This is clearly the place with most matches.

At the very least, we've shed (or gathered) light on a not so beaten patch of sky, and maybe even inspired someone else to take a deeper (or wider) look.
It was also a very good occasion to learn how to use databases to check for references and available data.

We hope you like it.

Clear skies,
the Astrodivers