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You are here: Home Telescopes Magellan Instruments PANIC Panic online documentation Observer Information Panic Observer's Manual HgCdTe Detector Linearity, Saturation, and Residual Charge

Linearity, Saturation, and Residual Charge

The detector becomes nonlinear at the 1% level at approximately 15,000 ADU and at the 5% level at approximately 30,000 ADU. The deviation from linearity is slightly dependent on the count rate onto the detector and the number of endpoints used. A useful mean solution for pixels above 8000 ADU is:

 
y = c0 + c1*x + c2*x2     (1)

 

 

where x is raw counts in a given pixel, y is the corrected counts, and the coefficients are:

 

c0 = 4.291443e + 01, c1 = 9.752524e - 01, and c2 = 1.962545e - 06.

 

This linearity correction is implemented in the lincor.cl IRAF script in the panic data analysis package.

 

Saturation occurs at approximately 45,000 ADU. Once the detector saturates the counts will roll over and it may appear there are almost no counts on the detector. This happens when the detector saturates or nearly saturates between the reset and the first read. If you believe you are close to saturation and your image does not reflect this, a quick check is to obtain a second exposure of double or half the exposure time.

No residual charge problems have been reported to date.

There have been no problems with ghost images with the exception of the Y filter. If you are using the Y filter, you may see a ghost in the upper left quadrant of the detector. The intensity of the ghost does not scale with sky brightness, and thus it may be caused by a light source in the dome. However, if the sky does not vary, then this ghost will disappear in sky-subtracted frames.

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