Linear Dark Current
- ISR-1997-026 -- Characteristics of NICMOS Detector Dark Observations.
- AAS Jan 1998 POSTER -- Understanding the NICMOS Darks.
- CALIBRATION WORKSHOP 97 -- Understanding the NICMOS Darks.
The examples are images of synthetic models of MIF512 darks that include effects of FAST readout modes. They show a combination of different anomalies such as linear dark current, shading, amp glow, and hot pixels.
The linear dark current is the traditional detected signal in the absence of any source illumination, and it scales linearly with exposure time. In NICMOS there is a spatial structure to this signal, with it being higher in the corners near the readout amplifiers. This is probably the result of heating by the amplifiers themselves, and is different from the amplifier glow (see section on amplifier glow). This signal has also been seen to be variable, and is probably temperature related.
All 3 cameras have a linear dark current of ~0.05 e/s near the center, and about a factor of 2 higher than that in the corners. There is also some evidence for quadrant dependence, which is not unexpected since each quadrant has its own amplifier.
A tool to allow users to generate synthetic darks is available. This tool allows the observer to vary the degree of dark current, amp glow, and shading to better match their data.