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Re: (meteorobs) Transmission Gratings
In message <v01510100aefa11259100@[204.215.138.179]>, Lew Gramer & Karen
Simmons <lewkaren@tiacdot net> writes
>
>Sounds like a very worthwhile project, Jeff. Please keep the list up to date!
>
>BTW, I've always wondered what exactly the principle is that photo-derived
>spectra are based on? Jeff or anyone, how do systems like IRAF work?
>
>Lew
>
Iraf has many different tools. The 'general' pakages are mainly for
reducing CCD photographs, and spectra. In my case the meteor spectrum is
from a b/w photographic print scanned on a flat bed scanner (to preserve
the spatial dimensions of the original). The image is stored as a
'.fits' file and imported into IRAF which converts the image to its own
format. The reduction of the second order spectrum was complicated by
the fact it was curved slightly, so IRAF is made to fit a polynomial
function to the curve of the spectrum so it will 'track' it.
Then by setting apertures, and a few other parameters the software does
some fancy pixel summing perpendicular to the dispersion direction and
produces a linear one dimensional spectrum plotted as an x-y graph.
In order to calibrate wavelengths The exercise is reapeated with a
spectrum of a known source such as vapour lamp, the resulting scale is
then fitted to the meteor spectrum.
This cuts a long storey short, but once the basics are grasped the
package is easy to use.
--
Jeff Lashley
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