[Aavso-photometry] Errors on AIP

[Arne Henden]

Michael Koppelman wrote:
> OK, hopefully the last update to this. This is a spreadsheet to 
> calculate uncertainties from the text output from AIP 
> (http://www.willbell.com/aip/index.htm).
> 
> I've updated it to use the S/N equation from "Handbook of CCD Astronomy" 
> by Steve B. Howell. The equations aren't numbered in that book but it is 
> on the bottom of page 55. It takes into account the gain and readnoise 
> of the CCD as well as the noise from the star itself and the sky. It has 
> a term for "dark current" which I don't use because I don't understand 
> why it is there since we all subtract that out of our data frames.
> 
> The spreadsheet is here:
> 
> http://www.lolife.com/astronomy/AIP_Err.xls
> 
Dark current noise is included because it is present in the image.
When you do your processing, where you subtract a master dark, that
removes the mean dark level but does not remove the noise.  In fact,
it adds noise to the processed image since there is noise in the
maste dark (albeit less than for a single dark frame).  Everything
adds noise!
Arne
that you subtract during processing.