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AnomaliesThis page will serve to document anomalies or odd behavior observed on WFC3. A brief description and links to relevant documents will be provided for each behavior. UVISCharge Transfer Inefficiency (CTI)
CTE data taken in TV2 on the backup UVIS detector indicate a current
charge transfer efficiency of >99.9999%. For a full description,
see the ISR below. CrosstalkCrosstalk on a CCD detector occurs when a mirror image of a source from one amplifier output appears on neighboring amplifier outputs. In effect, sources detected in one quadrant cause electronic mirror-imaged ghosts in other quadrants. In the WFC3 UVIS channel, the only measurable crosstalk occurs when pixels on the detector saturate. Detailed findings of the latest crosstalk investigation will be presented in an upcoming ISR. Filter GhostsGhosts due to scattering from the window and filters of the UVIS
channel have been observed in WFC3 ground testing. In all filters except
for two (FQ232N and FQ243N), these ghosts contain less than 0.6% of the
source flux. Typical ghosts are in the 0.3 - 0.4% range. For the two
filters mentioned above, the ghosts can contain up to 7% and 5% of the
incident source flux, respectively. IRDark Current TailThe dark current behavior of the pixels in the IR detector cannot be completely described by a single number. The distribution of dark current values across the detector is a skewed Gaussian, with a tail of high dark current pixels. The dark current distribution of the IR flight detector will be characterized in the upcoming TV3 testing. Inter-Pixel CapacitanceThe IR channel is affected by inter-pixel capacitance (IPC), in which the signal measured by one pixel is felt by its neighbors, resulting in an over-production of electrons. This can be thought of as an artificial increase in QE of the detector. From ground testing, we have determined that the effects of IPC can be removed by scaling the measured signal downwar by a factor of 0.88. This correction will be implemented in CALWF3. CrosstalkCrosstalk effects have been observed in the IR channel. Unlike the UVIS channel, crosstalk appears at very low levels (1e-6) for all point sources observed in the IR channel, regardless of whether the source contains saturated pixels. Details of the latest crosstalk investigation will be presented in an upcoming ISR. Filter GhostsUnlike the UVIS channel, no significant ghosts were observed in the IR
channel during TV testing. See the report below for details. |
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