SL-17 - Fenrir Nebula
Who’s up for a ghostly, spooky space wolf?
There’s not a lot of information about this nebula. It seems to be a very photogenic, but forgotten denizen of the night sky.
Located in the constellation of Scorpius, a huge cloud of dust blocks out the light from a glowing cloud of energised Hydrogen gas located behind it.
The shape makes a viewer envisage a wolf, endlessly racing through space in pursuit of it’s prey.
The nebula is catalogued as ‘SL-17’, and lies close to the nebulae ‘Gum 55’ and ‘The Dark Tower’. There are a further 40-odd dark clouds that are denominated by the initials ‘SL’ in various catalogues. I doubt many of them are as attention-grabbing as this one.
Because of it’s shape, the nebula is often referred to as ‘The Wolf Nebula’, or the ‘Fenrir Nebula’. In Norse mythology, Fenrir (or ‘Fenris’) is a giant wolf of incredible strength. The son of Loki and the giantess Angrboda, Fenrir is the brother to Jormungandr (the world serpent) and the goddess of the underworld, Hel.
Unlike my attempt to image the ‘Prawn Nebula’, I had no technical problems this time. (I expect that Murphy will pay me a visit when I next try to image the night sky. We can only wait and see.)
I have resolved the guiding issues that I suffered from previously by the simple expedient of ignoring conventional wisdom and not balancing my mount slightly counterweight-heavy. The convention seems to be that for gear-driven mounts, you reduce backlash within the gears (by slightly off-balancing it) so that the gears have a constant load on them. Which is all well and good, except that my mount has a belt-drive system, so there is no need to keep the gears loaded. Now that I have started balancing my mount, I was able to achieve an average tracking error of 1 arc-second for all the time I was imaging SL-17.
The camera rotator that I bought has also been added to the mount’s optical train. This allows me to keep the same camera rotation from one session to the next, and to alter the framing of the image to get a better aesthetic.
This image comes from 3 imaging sessions. Two long-duration sessions with the Optolong L-Enhance filter to capture the bright Ha background, with a short-duration session with the UV/IR-cut filter to capture the correct star colours.
Just to make things a bit more interesting, I imaged during the latest full moon. The general rule when using an OSC setup is “do not image a week either side of the full moon” because of the insane amount of light from the moon. (As an aside, when I was outside and my eyes got used to the light, I was able to see colours under the light of the full moon.)
All the data was stacked with ‘SiriLic’ and the basic processing carried out in SiriL. I used the new starnet++ integration feature to split the image into a ‘starless’ and ‘stars’ image pair before using Affinity Photo to recombine them into a single image for final processing.
Overall, I am happy yet unsatisfied with how my work came out. I feel that I can create a better image, but don’t yet have the image processing skills to do so. I am particularly annoyed by the huge amount of noise introduced by starnet++, but am not able to do very much about it at the moment.
Equipment: SW72ED @420mm / HEQ5-Pro / ASI183MC-Pro / SV165+SV305 / KStars/Ekos
Image Data session 1:
- Gain: 100
- Offset: 10
- Temperature: 0 degrees C
- Exposure: 180 seconds
- Frames: 80 Lights (4 hours integration), 20 Darks, 30 Flats, 30 DarkFlats
- Filter: L-Enhance (Ha + Oiii dual-narrowband)
Image Data session 2:
- Gain: 100
- Offset: 10
- Temperature: 0 degrees C
- Exposure: 180 seconds
- Frames: 60 Lights (3 hours integration), 20 Darks, 30 Flats, 30 DarkFlats
- Filter: L-Enhance (Ha + Oiii dual-narrowband)
Image Data session 3:
- Gain: 100
- Offset: 10
- Temperature: 0 degrees C
- Exposure: 30 seconds
- Frames: 30 Lights (15 minutes integration), 50 Darks, 30 Flats, 30 DarkFlats
- Filter: UV/IR cut filter
The entire frame
