Just managed to finish a project I had been thinking about for some time.
40 Eridani is a remarkable triple star system, consisting of a Main Sequence K1 type dwarf, orbited by a white dwarf and a red dwarf. The white dwarf was actually the first to be discovered, in 1783.
The image below is a RGBI composite, captured with an Atik 320E monochrome camera through ordinary Wratten type filters (#25 Red, #80A Blue, and #56 Green). The telescope was a Celestron Nexstar 6SE in alt-az mode. Each channel is the combination of approximately the 20 best images selected from around 35 exposures of 4 seconds each (so about 80 images, total exposure time of 320 seconds).
The 20 images for each channel were dark subtracted (but not flat fielded), aligned and stacked using the Astonomy plugins for ImageJ. The resulting R, G, B and I images were then de-rotated first by hand, then aligned using several passes of the Stackreg plugin, before being merged into a composite colour image.
I then used Gimp to smooth things a bit, and increased the saturation to emphasize the colour difference between the three components.
Half the purpose of this project was to see how practical this sort of imaging technique would be using a non-guided alt-az scope, ordinary visual filters, and no filter wheel. Have to say I'm pretty pleased with the result.
-Ivan
