Response Correction

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Andy Wilson

Hi Bill,

Reading your post I notice that you say:

“when you divide a meteor spectrum through by a stellar spectrum”

I’m not sure if this is what you really meant, as this is not how corrections are applied.

When creating a response correction you divide a stellar spectrum by a professional corrected spectrum for the same star, or at least by a standard spectrum for the spectral class of the star. This gives you your instrument and atmospheric correction. This is an imperfect process since the resolutions will be different resulting different line widths, the alignment may not be perfect, and you have atmospheric telluric lines in your spectrum. However, a smooth curve can usually be obtained by tweaking parameters and applying some smoothing to get rid of sharp bumps due to anomalies near absorption lines.

This is then your response correction. Robin’s links show this process with illustrations of actual spectra. You can the apply this response correction curve to a meteor spectrum.

The problem is this is best done with the star at the same altitude as the target. Otherwise the effect of increasing airmass has a big impact on the spectrum with decreasing altitude and the response correction will be wrong. So ideally you’d have an image with the same setup, but perhaps a longer exposure, that would include an A type star at the same altitude as the meteor. Of course the meteor is not at a single altitude so even this is not straight forward. A star at around the mid-altitude of the meteor might suffice as an approximation.

I also find it difficult to get a good correction at the extreme blue or red. When producing a corrected spectrum I just accept that I may have to crop off the extreme wavelengths.

Apologies if this is just going over what you already know.

Best wishes,