IC405 flaming star. Newt at f 900 mm

[timh]

Took the opportunity of two consecutive clear and moonless nights to have another go at the flaming star nebula while it is near the zenith. The aim was to choose a focal length to frame a reasonably large amount of the object and to better emphasise the reflection nebulosity and very bright type O star, AE Auriga over the really much fainter type II HA nebulosity in the final composition. The approach was very simple --combine the B and G channels from a simple unfiltered (aside from UV/IR) OSC image with an HA image as the red channel.

The first image is from 100 minutes (66s subs at unity gain) exposure using an ASI294 MC OSC. The second image retains the original RGB image stars stars (extracted using RC StarExterminator) but combines in 3h of HA image (3 min subs) at a gain of ~ 0.6 e/ ADU as the red channel obtained using a mono ASI294 MM camera and Optolong 7 nm HA filter.

PDS 200 Skywatcher at F 4.5 (0.9X coma corrector) on a CEM70 mount- guided using PHD2 and an 80mm achromat, f 400 mm ASI120 mini camera. Thus sampling was at 1.05/ pixel. Seeing moderate to FWHM ~ 3 arcsec.

Processing was in PixInsight. It was difficult to nigh impossible to remove light gradients from the unfiltered RGB image -- the new gradient correction tool did not work that well and repeated application of automatic background extraction produced the best result (still not perfect - residual gradient is still there) prior to star correction (some residual coma) and sharpening with Blur Exterminator and colour correction using the SPCC tool. Star Exterminator was used to remove and then eventually combine stars back in so that the starless image could be stretched using histogram transformation, arcsinh, exp and curve tools before reducing the noise using NoiseExterminator (RC) and then Affinity Photo for final adjustments of contrast and colour saturation.

AE Aurigae is a young main sequence star of the spectral type O9.5V. It is travelling quickly and originates from the Orion region -- It has a mass 23 times that of the Sun, a radius 7.47 times solar, surface temperature of 33,000 K and is ~ 60,000 times more luminous than the Sun. The type II H region that it is ionising is about 5 light years across -- the foreground bright reflection nebula comprises dust.

It is interesting to contrast the RGB only view with the view adding in the HA. In the former the wider HA region is only faintly visible as red. I suppose that - visually - because of the eye's response - if any hint of the wider nebula were to be seen at all it would appear as a faint blue/green due to to only the H beta being really within the eye's range ? HA filters and CMOS cameras really are amazing tools for making visible so much of the detail in the sky that would otherwise be invisible to us.


POSTEDIT. Actually - to be fair to PI - after watching Dave's two videos I find that the background correction tool did work pretty well for removing the background gradient -- it is just that I wasn't using the best parameters.

[admin]

Hi Tim,

both lovely images - looks like you spent the recent clear nights very profitably

I actually rather like the RGB only one - perhaps better than the H-alpha - the impression of a bright star sitting within and illuminating a cloud of gas/dust is stronger for me, and the hint of the H-alpha structure works well. You could imagine that view out of the window of the spaceship is some Isaac Asimov tale

cheers,

Robin

[timh]

Thanks Robin, yes I like the look of the simple RGB image better too - a bit of mystery about it and a better reflection (sorry poor pun) of the extraordinary nature of AE Auriga versus everything else in the field. It would have been better with a few more hours of imaging but the clouds came in. Tim