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Light
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The effect of CR on box_centroider centroiding algorithm.

 

Dataset:
all
 
Symptoms:

In all datasets, a few measured positions are only just slightly different from the mean levels (usually less than 1 pixels).  

 
Explanation:
For completeness, we looked at 5 of these for a WASP-15b AOR, and all 5 are caused by cosmic rays (CR).  The CR will change the center of light calculation in the centroiding routine.  Not surprisingly, but we have not quantified it, brightness of the CR seems to affect difference in position from the mean.   The rate at which we see the centroid deviations is consistent with the known CR rate. 
 
Figure 1: X and Y position as a function of time for a WASP-15 AOR. The position points which do not follow the sawtooth pattern are caused by CRs.
 
 
Figure2: Images of the targets where the position centroids are offset from the mean values. Every case has a cosmic ray in the field of view which affects the centroiding algorithm.