Super Bubble In Dorado
I was “wandering” around the sky map in Telescopius, looking for something interesting to image, when I stumbled across something unusual. A large DSO that wasn’t in any of the catalogues I looked at. I had the co-ordinates, but nothing matched it. How unusual. There were plenty of NGC entries all around it, but this one didn’t have an NGC identifier.
I asked the question on IIS - “What is this DSO?” and whilst I waited for people to answer, added the co-ordinates into my custom catalogue in KStars, got the rig outside and running.
I have to say that the conditions that night were almost perfect. No clouds, no haze, perfect seeing, and the position of the target was high enough that I wasn’t fighting the light pollution ‘dome’ like I usually do. The average guiding error over the night was less than 1 arc-second. The lowest RMS value I saw was 0.47 arc-seconds.
For some reason the auto-focus module played up again. I lost patience with it after the ‘V’ curve turned into a flattened ‘W’ shape; so manually set the focus position to a point where I knew it would be focused. (It was a bit disappointing to see Ekos report ‘No stars found’ when I could clearly see a star within the sub-frame.) It might be time to revisit my settings and see if anything can be done to resolve this.
In the meantime, a very helpful member of IIS had identified the mystery DSO. My thanks to you again, Brian!
It’s known as the ‘Super Bubble In Dorado’ and has been catalogued as ‘Henize 70’, N70, LHA 120-N44, and DEL-L-301. (Confusingly, Wikipedia gives it the catalogue ID of ‘LHA 120-N70’.)
OK, that’s all well and good, but what is it?
After all that, it’s an emission nebula and ‘super bubble’ that may also have characteristics of being a super-nova remnant (SNR). The scientists are not in agreement about exactly what it is.
Size-wise, it’s been measured at about 300 light-years in diameter and is roughly 170,000 light-years away from us.
Wikipedia says
Henize 70 was first observed in 1950 in a survey of bright planetary nebulae, based on appearance it was proposed that it might be a supernova remnant. In 1956, it was added to a catalogue of Hα emission stars and nebulae by Karl Gordon Henize, where it was described as an emission nebula instead of a planetary nebula.
In a paper published in 1978, it was proposed that stellar winds could be a major part of the formation of Henize 70 and other emission nebulae. Later, in a scientific article 1981 it was mentioned that it was more likely from a supernova explosion rather than stellar winds. Another study in 2014 measured high SII and Hα ratios, indicating that it is not a supernova remnant.
Henize 70 has spectral line ratios relatively similar to that of supernova remnants due to having similar SII/Hα line ratios although most supernova remnants have higher NII/Hα line ratios.
Astrodrudis says
N70, a rather peculiar nebula located in the Large Magellanic Cloud (LMC) is very often described as a superbubble. The exact nature of this bubble-like nebula is not fully understood (or at least, decided). As early as 1981, Rosado et al. published an article in Astronomy and Astrophysics giving clear hints (not confirmations) that the shape of N70 was due to shock waves, that “should be attributed to an old supernova explosion”. In 1999, Skelton et al. take this nature for granted but, in 2014, Zhang et al. stated that it is not yet confirmed that N70 be a SNR. What we know, despite its real origin, is that N70’s morphology has been also shaped by the OB association LH114, a tight group of hot O and B stars located at the center of the bubble.
You can read the rest of the article here: https://astrodrudis.com/n70-henize-70/
On top of that, an image of this DSO was twice selected to be a NASA APOD, back in June of 1998 and February of 2019.
Regardless of what the scientists say, I managed to get a cool image out of my data. I think I’ll go back and get more data on it - there’s plenty of cool swirls and twists in the gas clouds that need clearing up. There’s also some Oiii hiding in there, and more data will bring out the faint blue/green colours.
Because the target is quite small in my telescope’s FoV, I decided to try what’s called ‘binning’. By combining four adjacent pixels into one, you can effectively magnify your image by a factor of 2. It also allows you to collect more light in the same exposure length. At least that’s how I understand it. (I’m probably wrong!)
Of course, all your calibration frames also need to be at the same binning setting. No prizes for guessing who forgot to do this with his Flats and DarkFlats calibration frames… So the image below has only Light and Dark frames, on the up-side I was able to hide the imperfections that the Flats/DarkFlats would usually remove.
Update: 2024-01-11
Well, we had clear skies for the second night in a week. I took advantage of the clear skies (even if they weren’t as dark as I’d like them to be) and got another 2 hours worth of photons captured. I would have stayed out much later, but I had to get up for work the next morning.
I then used Sirilic to stack both sessions worth of data - along with fresh Flat and DarkFlat calibration frames. (These got applied to the data from session 1 - it’s not perfect, but all the dust marks seemed to be in the same position, so why not?)
With the additional data, I can see more of the detail in the heart of the bubble and the ’tendrils’ of gas and dust seem a lot more solid than in image 1. The colours are a bit different to those in image 1 due to the extra H-Alpha data, as well as differences in how I processed them. I may have a workflow (as simple as it is) but I cannot replicate exactly the same tweaks in each image. I work until it looks “good”, leave it for a day or so and then revisit to make final tweaks.
I also used James Ritson’s ‘Star Eater’ macro to calm the stars down a bit so the nebulosity stood out better against the background.
Looking at the two images side-by-side, I can see that image 1 is quite a bit brighter, and that gives the impression there’s more detail with in the bubble. This is a bit of an illusion - closer inspection shows that image 2 has more detail. It’s just not quite as obvious.
Session 1 data:
- Gain: 120
- Offset: 10
- Temperature: 0 degrees C
- Exposure: 120 seconds
- Frames: 60 Lights, 25 Darks, (120 minutes integration in total)
- Binning: 2x2
- Filter: Optolong L-Enhance
Session 2 data:
- Gain: 120
- Offset: 10
- Temperature: 0 degrees C
- Exposure: 120 seconds
- Frames: 60 Lights, 25 each of Darks, Flats and DarkFlats (120 minutes integration in total)
- Binning: 2x2
- Filter: Optolong L-Enhance
Processed with SiriL (stacking via Sirilic, then pre-processing, basic stretching and star removal with Starnet++ in Siril) before recombining and tweaking in Affinity Photo v2
Equipment: SW72ED@420mm / HEQ5-Pro / ASI183MC-Pro / SV165+SV305 / Kstars/Ekos
Image 1 - LHA 120-N44 (aka Henize 70)
