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Optimizing
Analysis
Techniques
for
Exoplanet
and
Brown
Dwarf
Light
Curve
Studies

Datasets
Examples of known noise pixel spikes
Planetname AORkey start_sclk stop_sclk
HD7924 r46981888      1041429073.301 1041455525.016
HD7924           r44605184       1004594183.339 1004622735.006
XO3                 r46482944      1050530251.708 1050573212.475
HD20003         r48408064      1062587169.546 1062628187.337
 
 
Symptoms
A few times over the course of the mission, noise pixel has been seen to sharply increase in value for a short duration (~30 min) before returning to normal (See Figure 1, 16&30 hours).  These noise pixel spikes are alarming because as noise pixel goes up, the measured aperture flux will decrease which mimics the signal of a transit. During the spikes, positions don’t show out of the ordinary trends.  There is also no apparent correlation with any particular spot on the pixel, so these are not related to a single position.
 
Explanation
Using the IRAC data simulator we have successfully replicated the noise pixel spikes seen in these datasets using a high frequency position oscillation.  At frequencies higher than the observation rate, oscillations of the instrument will have the effect of smearing out the image, and thereby increasing noise pixel, without changing the object centroids (see Figure 2).  A discussion of this was presented at the AAS workshop.  Although we have looked for correlations with telemetry values, we do not yet know what could cause the suggested oscillations onboard Spitzer.
 
Simulated data including noise pixel spikes