Sharpless 2-142: The "Wizard" Nebula...

Sh2-142: The "Wizard" Nebula...

Object: Sharpless 2-142 (Sh2-142), with open cluster NGC 7380
Type: Emission Nebula and open cluster
Constellation: Cepheus
Distance: 9700 light years

Dates: 29th November, 2nd and 3rd December 2019
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 16 x 600s H-alpha, 16 x 600s SII, 16 x 600s OIII, no flats/darks (hot pixel removal in Astroart).

Sharpless 142 is a diffuse emission nebula surrounding the developing open star cluster NGC 7380. NGC 7380 was discovered by Caroline Herschel in 1787. William Herschel included his sister's discovery in his catalogue, and labelled it H VIII.77. The nebula itself is very faint and eluded the eagle-eyed Herschels.

Stellarium map showing location of Sh2-142

It can be found in the constellation of Cepheus, which is virtually overhead during autumn evenings in the UK. The nebula occupies an area approximately equal to that of the full moon, but is very difficult to see visually with telescopes, especially from suburban locations

The nebula spans about 140 × 75 light-years in space and lies within our Milky Way Galaxy.

 

The Sharpless designation comes from the Sharpless catalogue of 312 emission nebulae (H II regions). The first edition was published by Stewart Sharpless in 1953 with 142 objects (Sh1) and the second and final version was published in 1959 with 312 objects (Sh2).

The cluster and nebula are part of an even larger and optically invisible molecular cloud designated NGC 7380E, estimated to contain 6000-15000 solar masses of dust and gas.  It is believed that the star formation that created the stars of NGC 7380 began some 4 million years ago and continued for another 2 million years before it largely ceased, with radiation from the stars dispersing the cloud from which they formed and ionising the remaining gas to produce the emission nebula we see today.

Mist and freezing condensation terminated all three imaging sessions before midnight. Auto-guiding was also a pig, with an RMS of anywhere between 0.7 to 1.2, giving rise to rather poor resolution and bloated stars. I'm not sure whether that's down to the mount (balance seems absolutely critical) or poor seeing. The seeing certainly wasn't good for any of these sessions: I could see the focus star rippling violently whilst trying to get a sharp focus, which in the end just turned out to be a best guess. 

The Ha, SII and OIII frames were stacked in Astroart and then RGB combined in PaintShop Pro. A blend of 50: 50 SII/Ha was used for the red channel, 30:70 Ha/OIII for the green and 100% OIII for the blue, with further curve changes, star reduction and denoising in PSP to give the final image. This was the first time I had tried adding some SII data into the mix, and it certainly seems to add some contrast to the final image.

The colloquial name of “the Wizard” alludes to an apparent figure in a pointy hat that can supposedly be made out in the nebulosity but like so many of these more recent monikers, I’m not sure I can see it myself.  Maybe it looks more like Roy Wood....