NEW DISCOVERIES: SNR G321.3 -3.9/the Hidden SNR & PN Candidates StDrLu 1-7

[matlud]

Hi Everyone,

I am very pleased to share the results of a project I have worked on over the past 18 months with Professor Robert Fesen from Dartmouth, Marcel Dreschler from Germany, and Xavier Strottner from France. During this time I took deep SHO images of the supernova remnant SNR G321.3 -3.9, which we refer to as the Hidden SNR. From this image we also made an incredible 8 new PN candidate discoveries: STROTTNER-DRECHSLER-LUDGATE (StDrLu) 1 through to 7 and STROTTNER-DRECHSLER-LUDGATE-LE Dû 1 (StDrLuLDû 1).

https://www.iceinspace.com.au/forum/attachment.php?attachmentid=302776&stc=1&d=1677454638
https://www.iceinspace.com.au/forum/attachment.php?attachmentid=302777&stc=1&d=1677454638
Full FOV Astrobin: https://www.astrobin.com/full/gcnpfw/0/
Tighter crop Astrobin: https://www.astrobin.com/full/gcnpfw/B/

In June 2021, I was invited to be involved in a project on a potential new SNR located in Triangulum Australe. Marcel had detected a number of promising signs on SUMSS radio survey data and also on SHS H-alpha images suggesting a possible SNR. The next step was to obtain deep SHO imaging to both help confirm a SNR, and to identify suitable slit locations for future spectroscopic investigation with larger professional telescopes. Subsequently, I gathered over 100 hours of data during the end of 2021 and 2022 to capture this beautiful but extremely faint object.

SNR G321.3 -3.9
The Hidden SNR has been previously identified as a potential SNR candidate in galactic radio SNR survey literature, including the the Molonglo Survey of 2014 (https://arxiv.org/pdf/1410.8247.pdf) and the Parks 2.4 GHz radio survey (http://articles.adsabs.harvard.edu/pdf/1997MNRAS.287..722D). However, it has never been confirmed as a SNR. This image is the first time the Hidden SNR has been detected in optical wavelengths, and provides strong supporting evidence that G321.3 is a true SNR.

The Hidden SNR has numerous OIII filaments, which form a well defined shell measuring 1.8 x 1.1 degrees. The OIII emission closely matches the radio morphology, which supports a SNR origin for the nebula. There are filaments to the North and West of the main SNR, which are located outside of the radio emission, and these likely represent large outbursts from the main SNR shell. In addition to the OIII emission, numerous Ha and SII filaments can be seen. These filaments have a high SII:Ha ratio demonstrating that this gas has been shock heated, further supporting a SNR origin.

https://www.iceinspace.com.au/forum/attachment.php?attachmentid=302779&stc=1&d=1677454638

Collecting further data on this SNR is challenging. The SNR filaments are very faint, and are quite diffuse. They are located in a dense star field and in a complex region with numerous molecular clouds and photo-ionised gas from the nearby Circinus OB association. As a result, larger scopes with a smaller FOV and much smaller pixel scales still require significant exposure times to detect the filaments. At the current time, high resolution spectroscopy with a 10 metre telescope using slit locations determined from this data is planned to confirm the SNR nature of the nebula.

NEW PN CANDIDATE DISCOVERIES
In addition to the Hidden SNR, numerous other nebula were visible through the image field. Careful analysis of the image revealed a total of 8 new PN candidates, which have been successfully registered as STROTTNER-DRECHSLER-LUDGATE (StDrLu) 1-7 and STROTTNER-DRECHSLER-LUDGATE-LE Dû (StDrLuLDû) 1.

https://www.iceinspace.com.au/forum/attachment.php?attachmentid=302778&stc=1&d=1677454638
Starless with PN Candidates Annotated Astrobin: https://www.astrobin.com/full/gcnpfw/C/

Of special mention is the candidate StDrLu5. This fascinating candidate is located within the SNR shockwaves. It has characteristic inner OIII emission surrounded by some Ha emission. However there is also striking asymmetrical SII emission to the West of the candidate, which is the aspect is facing towards the expanding SNR shockwave. This raises the strong possibility that an interaction between the SNR shockwave and the PN candidate has occurred.

If the Hidden SNR is interacting with StDrLu5 then the SNR and PN must be located at the same distance. We identified the CSPN of StDrLu5 on DeCAM images, and this star has a g magnitude of 20.76 and a parallax of 0.712 milliarcseconds/year which equates a distance of 1.40 kpc. Given the Hidden SNR's angular size of 1.8 x 1.1 degrees, this translates into a physical size of ~ 44 x 27 pc, which is about the same size as the Cygnus Loop (Veil Nebula).

https://www.iceinspace.com.au/forum/attachment.php?attachmentid=302780&stc=1&d=1677454638
StDrLu5 Astrobin: https://www.astrobin.com/full/gcnpfw/D/

ACKNOWLEDGEMENTS
Many thanks to Prof Rob Fesen for his scientific support and for involving me in this project.
A special thanks to Marcel Drechsler (Team StDr) for generously sharing his knowledge and processing expertise, and for his expert project organisation and assessment of potential candidates.
Thanks to Xavier Strottner (Team StDr) for his help in analysis and registering the new candidates.
Thanks to Pascal Le Dû for his analysis and registration of the candidates.

Telescope: Nikon 400mm f/2.8
Camera: ASI 6200mm
Filters: Chroma 5nm SHO + RGB
Mount: 10Micron GM1000HPS
Location: Dunedin, New Zealand

PROCESSING NOTE
The emission lines in this image are extremely faint, and have been processed using subtraction techniques with any small artefacts logically filled. For those interested, Vicent Peris has published an excellent overview of an implementation of the subtraction technique https://pixinsight.com/examples/M31-Ha/. Noise reduction was performed using PS and Topaz DeNoise with careful attention to ensure no new detail was introduced by the NR process.

Cheers,
Mat

[strongmanmike]

Great news and interesting write up Mat, why make a single discovery :shrug:... when you can make bloody nine! :eyepop: :lol: Well done to the team :thumbsup:...and as an extra bonus, you have produced a unique, quite beautiful, not to mention deep, image of an an otherwise rarely shot bit of sky. Now you need to team up with the other ultra deep Kiwi guru, Rolf Olsen, one can only imagine what the pair of you might discover together :eyepop: ;) :)

Slightly off topic but still relevant?...Your processing note is interesting too. In this new age of AI sharpening software/plugins, it seems to matter which software/plugin you actually use and the technique applied. While in this case your discovery is not about the fine details revealed anyway but rather the existence of the whole object and I am not an expert but in relation to many other images, enhancing fine details, based on learning what astronomical detail looks like in lots of other images, seems fraught with issues...:question: eg. what if the neural networks learn from lots of poorly enhanced details in some/many of those images?

Mike

[matlud]

Thanks Mike! the project kept us very busy 😀 As you mention, this patch of sky has been quite overlooked by amateurs and also professionals, which certainly helped in making the new discoveries. I think the very dense star field is a big factor in this, and it created its challenges with processing. Working with Rolf would be great! He is a major inspiration for my imaging, and his deep images are just fantastic.

Discussing the role of AI in astro processing can seem a bit like opening pandoras box 😂 For sharpening and noise reduction afaik there is the Xterminator range (which I understand was trained on Hubble data that was convolved, so it represents a best case scenario as far as detail) and Topaz. One criticism of Topaz is it is mainly trained with terrestrial images but in both cases it’s a bit of a black box to most of us as to exactly what the neural network is doing. Like all tools I think you can go too far with them and create artefacts, but if you use them carefully and compare back and forwards with your raw data to make sure its enhancing what you have captured, I think they are useful.

[strongmanmike]

Everything you say there sounds pretty spot on to me. It just feels like every time I see an image these days, that looks detailed, I am second guessing how it was done and whether that detail is real or kinda conjured and even made up :shrug: I used to be good at picking the filters used in processing and when they were applied too heavily but this new AI based filtering palava is much more tricky. As you say, it's fairly easy to keep an eye on changes in your own data, as you progress the processing but having to blink others images, just to verify it's reality, is more of a pain...and what to blink it with? Hubble? :shrug: :rolleyes: Not that I want to, but certainly no chance of checking your image, its a brand spanking new object :lol: :thumbsup:

Anyway, sorry for nudging the lid of Pandoras box :face: and again, very well done to you and the team :clap:...and look forward to some Olsen-Ludgate brilliance :)

Mike

[Bassnut]

wow, thats amazing !. Such an excellent image too, very interesting.

[Addos]

outstanding effort being part of this project! marcel and xavier and collaborators seem to be redefining the standing of the 'citizen scientist' in the last few months, very exciting times in astronomy! congrats for your discovery!

[matlud]

Thanks Fred!

[matlud]

Thanks Adam! It was a great Pro-Am collaboration, and great to be able to contribute to advancing the science. Pretty amazing what is still hiding out there. Cheers, Mat

[Peter Ward]

Remarkably impressive.....and well deserved kudos. :thumbsup::thumbsup:

[matlud]

Thanks Peter!

[Andy01]

Fantastic image & great to see the role amateur astrophotographers can play in real discoveries in astrophysics - congratulations to all for your dedication to reveal this thing, it’s beautiful! :)
Some serious hours went into that and the hard work certainly paid off, very well done! :thumbsup:

[TrevorW]

Very interesting and some great images nicely captured :)

[dvj]

Not only is this a fantastic image and resulting discoveries, the processing is exceptional. The depth of the nebula details and tiny stars is breathtaking. I have this region in hydrogen-alpha, but it only shows a narrow slice of what is in this image.

[Paul Haese]

Awesome to be a part of a discovery but I do really like the processing and palette of this image. Certainly a unique view. Well done to all involved.

[matlud]

Many thanks Paul, John, Trevor and Andy! Processing was a good challenge given how faint everything is and also the dense star field but I was really happy where it all ended up. Cheers, Mat

[ahmed_haider]

Congratulations on the discoveries!
The pictures look like a perfect combination of art and science, scientific in processing and artistic in rendering the colors
Amazing work!! Thanks for sharing

[g__day]

Very impressive - heck I am in awe!

[alan meehan]

Great Discoveries and brilliant images well done.

[Nikolas]

Great discovery, What an achivement!!
I'm a bit of a novice (alright a big novice) so where in the sky is this? What focal length was used? I may have lost it in all the reading

[gregbradley]

Awesome work Mat.

Greg

[joshman]

This is phenomenal. Not only is the image itself just amazing, but the scientific merits is amazing in it's own right. Definitely soemthing to be incredibly proud of. Congratulations to the entire team.

And... I've added the Hidden SNR to my list of target to image.