SNR G115.5+9.1, better known as “Scylla”, is a recently discovered Supernova Remnant Candidate (SNR?) in the constellation of Cepheus, making it a rare high-galactic-latitude SNR. Given its recent discovery, not much information about the SNR is available, meaning that neither its age, expansion speed, nor distance are known at this stage. With this in mind, we won’t be able to go into much detail in this write-up and will instead focus on analysing the data at hand.

Scylla was first published in April 2025 by Marcel Drechsler et al. and has since been photographed by only three other hobbyists on Astrobin. Its unique morphology and location in an IFN-dense field make for an interesting region in the night sky.

This is what made Scylla interesting for the Deep Sky Collective – our plan was to go even deeper than the initial discovery picture and in doing so have a closer look at the exact small scale morphology as well as full extension of the SNR.

Given these objectives, our goals were set on primarily getting narrowband data along with enough broadband for a clean continuum subtraction as well as the extensive IFN in the region. Similar to our KX And project, for narrowband we decided to solely focus on H-alpha and [O III] in an attempt to maximise SNR – we only got 5h of S II to check if anything would show up, while it did, the data was not enough to use in the final edit, resulting in a pure LRGBHOO image. In the end it turned out that the H-alpha and [O III] were brighter than expected so we could have added [S II].

In the Deep Sky Collective, we started imaging Scylla in August 2025 and imaged for about four months. Given other projects had to be finished first, pre-processing only started in February, directly followed by post-processing of the data. We had a total of 13 people working on the project — two Editors, one Stacker , ten Photographers, and myself coordinating, with some of us taking on multiple roles. In the end, we managed to get a total of 538h15m of integration, about 200h of which are dedicated to both H-alpha and [O III] and the rest mainly consisting of LRGB data, along with a tiny bit of [S II].

Before getting into any details in the picture, I want to thank everybody who contributed to this project. As always, it was a pleasure working together with everybody and seeing that continued effort!

Tim Schaeffer - Coordinator

Carl Björk - Stacker and Photographer

Steeve Body - Editor

Nicolas Puig - Editor

Jasper Capel - Photographer

John Dzibua - Photographer

Justin P. - Photographer

Stephen Guberski - Photographer

Akash Jain - Photographer

Jim Matzger - Photographer

Logan Carpenter - Photographer

Alpha Zhang - Photographer

Jeff Schilling - Photographer

Special thanks to:

Carl, who once again did a phenomenal job hosting and stacking all the data.
Steeve and Nicolas for the amazing edits you see today.

Interesting features in our image

Scylla in HOO

As mentioned in the beginning of the write-up, Scylla is a Supernova Remnant Candidate (SNR?) with an interesting morphology that has not been fully understood nor explored in a research paper yet.

The goal of this project was to go deeper than the existing images and provide high SNR data that lets us explore and present the small scale details without excessive denoising.

As mentioned, we focused on just H-alpha and [O III], aiming to fully reveal all features in these wavelengths. We did not attempt any significant [S II] although that certainly would have been interesting as well.

In the end our H-alpha data revealed the full shell, as well as many previously unknown details, along with what we believe is foreground H-alpha in the form of “curtains” running across the image. Being super careful with processing and carefully applying continuum subtraction we believe this is the most accurate representation of Scylla’s morphology yet. Due to copyright issues we will not include any data comparisons and leave that to anyone interested.

Next, in [O III] we picked up additional, fainter extensions of the SNR as well as previously unknown details. The bright star in the main [O III] bow made processing a challenge but we think we managed to tame it as much as possible.

In the figure below, the three main channels as well as the final edit are presented – note that the H-alpha and [O III] channels are fully continuum and median subtracted.

Scylla data left to right, top to bottom – Ha, [O III], Lum, Final image (Steeve’s edit) - © Deep Sky Collective

Potentially new discovery

This project came with a surprise which we believe might be a new discovery, likely to be a Planetary nebula or similar. The object in question forms a double-sided bow, similar to the Goblet of Fire but smaller. We believe this double-sided bow to be a strong indicator for it being an isolated structure and not part of Scylla. While there’s a White Dwarf (WD), it is right outside the shell, leaving us with no promising central star. Central coords are 23 28 18.543 +70 57 23.21 (SIMBAD query).

Updates will be added to this page once available.

Potentially new discovery next to Scylla – wide field and close-up – © Deep Sky Collective

Two edits

Our Scylla data is published in two versions:

Version A – Steeve’s version
Version B – Nicolas’ version

For any further questions about the project, feel free to reach out to us using the contact form or by leaving a comment!

If you want to see our image in greater detail, feel free to go to our website gallery, where the image is uploaded in full resolution ( 6401 × 4190 px), enabling you to explore the picture by yourself and zoom in on every tiny detail!

Integration overview

The final integration count, from only 10 photographers, is:

A massive thank you to everyone’s efforts!

We hope that you enjoy this image!

Text written by Tim Schaeffer, organiser and co-ordinator of the project and fact checked & proofread by the DSC team.