[Aavso-photometry] Question concerning linearity of CCD chip

[Wolfgang Renz]

Hi Larry

It depends on how you group the words.
Find the average [in the 5 exposures] of ---
the maximum ADU values for each star at a given exposure

He probably does mean to take the max pixel value (in ADU)
of the star image on the CCD which is spread due to diffraction
and seeing not to a single pixel but to a PSF disc.

Or does he describe to do aperture photometry before ?

Clear skies
 Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO



----- Original Message ----- 
From: <actuary at mchsi.com>
To: <Aavso-photometry at mira.aavso.org>
Sent: Saturday, September 22, 2007 6:55 PM
Subject: [Aavso-photometry] Question concerning linearity of CCD chip


> To All:
> 
> I am reading "Lightcurve Photometry and Analysis" by Brian D. Warner.  On page 
> 91, a procedure for testing the response linearity of a CCD chip is 
> described.  I am confused as to the meaning of the sentence "Find the average 
> of the maximum ADU values for each star at a given exposure...".  Say 5 
> imagess at 1, 2, 4, 8, and 16 second exposuress are taken. For a specific star 
> there are 5 images at 1 a second exposure.  Takling the maximum ADU for the 5 
> images for the specific star provides a singlr value.  However, the procedure 
> says to find the average of the maximum ADU values ... The average of the 
> single value is the same value. Since the test involves plotting the values 
> obtained through the application of the "averaging.. maxumum" algorithm by 
> exposure time, one does not average over exposure time nor over all stars.  
> Clearly I am misinterpreting the description of the procedure.
> 
> I would appreciate some guidance as to the correct interpretation of the 
> procedure.
> 
> Thanks
> 
> Larry