Thursday, November 1, 2012

The Wonderful World of Color

During the final days of Engineering Verification, we took a three-color (gri) dither sequence - that is, a set of 9 offset exposures in each of these three bands to produce a color image.  The object was the Bubble Nebula (NGC 7635), and I posted a single band image in a previous blog entry.  Now that we are working on the pipeline, it is our intention to produce a nice color image to advertise the capability of pODI.

Well, Ralf Kotulla, our commissioning working group observer from U. Wisconsin, beat us to it.  He took the 27 images, used swarp to align and combine them, and produced this nice color image.

Since we used g, r, and i, and since H-alpha, which dominates the nebular emission, is in the r band, if we had assigned g, r, and i to the colors blue, green, and red, the nebular would have been bright green.  Ralf decided to mess with our minds, and so he assigned g, i, and r, to blue, green, and red, respectively.  Thus, the nebula is reddish, but the stars tend to be green.

We are working on an "official" version of this, and we'll post it when it's ready, but this gives you and idea of what nice images pODI will produce.  Thanks, Ralf.



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