The Flaming Star Nebula (IC 405) is around 1500 light-years from Earth, and measures 5 light-years across. Its stand-out feature is the bright flaming star itself, AE Aurigae, seen as the brightest point in this image. It wasn’t formed in this nebula, but rather in the Orion Nebula around two million years ago. Two pairs of binary stars collided, and the flaming star was flung out into space, making it what’s known as a runaway star. At our point in time the flaming star is passing through this nebula, lighting it up from the inside.
The weather in the UK has been really terrible lately, so this imaging project took nearly seven weeks to complete. By the end this target was getting pretty close to the horizon!
In order to decide which filters to use, I did a bit of research on the target. It’s a reflection and emission nebula. Reflection nebulae are broadband targets, so are best imaged in RGB. For the RGB, I collected 15 hours of data using my new broadband light pollution filter: the Optolong L-Quad Enhance (review here). It’s the only broadband light pollution filter I’ve tried that has actually improved the quality of my data. Emission nebulae, in contrast to reflection, are often best seen in narrowband wavelengths, with the Flaming Star Nebula being a very rich source of Hydrogen-alpha. So, I then collected another 15 hours of data, this time using my faithful Optolong L-Ultimate (review here). That’s a dualband filter that collects Hydrogen-alpha and Oxygen III.
During processing I combined these two sets of data (RGB and Ha/OIII) into one single image. Scroll down for a PixInsight processing video that walks through how I did this. For interest, I made quick edits of just the RGB, and then just the Ha/OIII images. You can see them in the slider image below. RGB is on the left, and Ha/OIII is on the right. Hopefully you can see how each set of data has added detail to the final version. The RGB in particular really highlights the nebulosity around the flaming star itself; not surprising considering that’s the reflection nebula part. RGB is also good for giving accurate star colours. The Hydrogen-alpha gives unparalleled detail in the emission nebulosity. Combine the two and you get the final image, which I hope is the best of both.
Note that I scarcely detected a hint of Oxygen III. If I were a mono imager instead of OSC, I could have used the more efficient method of simply using a Hydrogen-alpha filter for all the narrowband component. But still, I think my OSC approach worked just fine.
As well as introducing the Optolong L-Quad into my workflow, I made another change: increased subframe length. To date, I’ve always shot 120-second subframes. For this image, and going forward, I’m switching to 300-seconds. The reason is simple: I gather so much data that 120-second subframes are filling up my harddrive and taking an age to integrate on my computer. 300-second subframes mean I have fewer subframes to store, and integration is faster. My mount is tracking well enough to allow me to do this. There’s a common misconception that I’ll very quickly address, which is that you need long subframes to get detail in your images, particularly from light-polluted areas. This might seem logical, but it’s not actually true. Using modern camera sensors with CMOS chips, as I do, means that your subframe duration doesn’t matter as far as image quality or discernible detail is concerned; it’s all about the total integration time. So, my decision is purely to save harddrive space and spare my PC from melting during integration! For more info about this, check out my article on how to get long integration times.
Imaging details
* 18 January to 3 March 2024 (6.5 weeks)
* Bristol, UK (Bortle 8)
* Telescope: Askar 130PHQ Flatfield Astrograph
* Camera: ZWO ASI 2600MC-PRO
* Mount: Sky-Watcher EQ6-R PRO
* Guide: William Optics 50mm Guidescope with 1.25″ RotoLock; ZWO ASI 120MM Mini
* Control: ASIAIR Plus
* Software: PixInsight, Lightroom
– PixInsight Pre-processing guide
* Filters:
– Optolong L-Quad Enhance (RGB) 180 x 300 seconds (15 hours)
– Optolong L-Ultimate (Ha/OIII) 180 x 300 seconds (15 hours)
Total exposure time: 30 hours
By Lee Pullen
Processing walkthrough
Example source data
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