Sh2-171 in HST Palette


Chris Heapy

Macclesfield, UK

The telescope used was a TeleVue NP127is refractor mounted on a Losmandy G11 equatorial mount. This was guided using a TV Pronto and SX Lodestar guidecamera. The CCD camera was an Atik 490EX.

Sh2-171 is an emission nebula in Auriga, and it contains a young cluster of stars (designated NGC7822) which only formed a few million years ago. A point of interest is that this cluster contains one of the hottest stars ever discovered (viz. BD+66 1673). The star in question is an eclipsing binary and the primary exhibits a temperature of 45,000K with a luminosity 100,000 times that of the sun. This star and others in the same group are actively carving out the centre of the molecular gas and dust cloud, the outflow of intense UV radiation and stellar winds forming the typical ‘Elephant trunk’ type formations around the eroded edge of the nebula, and at the same time exciting residual clumps of gas to emit their own light (hence, an ‘Emission Nebula’). It is easy to find the star cluster in the image – just look at the trunk formations which together point like accusing fingers at the guilty party! The image also contains many overlying dark structures which are clouds of dust and gas lying in the foreground and seen as silouettes.

This image is a composite of three wavelengths of light emitted by hydrogen-alpha, Oxygen III, and Sulphur II mapped to the visible spectrum as Green, Blue and Red respectively. Astrodon 3nM bandwidth filters were used to capture sub-frames for each channel which were then stacked before combining to make the final processed image you see here. A total of 10 x 20min sub-frames were captured for each channel.