NGC 1931 (Aur)

NGC 1931 (Aur)

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Date/Site: 19. December 2009, AAR-observatory in Presberg
Exposure/
Filter:
RGB 10 x 5 minutes (-25°C)
Camera: SBIG ST10XME, motorized Atik-filterwheel with Astronomik-RGB-filters
Optics/
Instrument:
26 cm-Newton on Gemini 41 Observatory
Focusing with Robofocus
Darks, flats, deblooming, alignment and stacking: MaximDL,
Levels and curves: Photoshop CS.

NGC 1931 is a very young compact cluster associated with Sharpless 2-237, a complex of emission and reflection nebulae. I have often seen it in the bavarian alps through mirrors from 6 to 20 inches but only in the last years we realized that not one but a very tight quadruple star illuminated the glow. The fainter stars of the cluster immersed in the emission nebula were swamped by its light. This was always one of my favourite deep sky-objects.
Conditions for the first RGB with the 26cm-Newton were almost perfect: no moon, minus 20,5°C, no wind, negligible glow.
After a thin layer of haze had settled as frost the limiting naked eye magnitude reached 6.0. MaximDL showed FWHM-values around 1.4, something that never happened before on this site.
In this night I shot 18 luminance-image, but they do not match the RGB-field due to image rotation after pier flip. in addition they were not properly focused.

© Friedhelm Hübner, last revision:  20.08.2022