NICMOS has four detector readout modes that may be used to take data. After the observing time has been approved, the readout mode will be selected by the observer when completing the Phase II proposal entry. However, potential observers may want to understand the characteristics of the NICMOS readout modes to help design their Phase I proposal.
There are three supported readout options:
The basic scientific rationale behind each of these modes, and a summary of their capabilities is outlined in Table 8.1, along with a recommendation regarding their use. The Phase II proposal instructions needed to identify the readout modes are given in brackets under the mode name.
Mode |
Use |
Functionality |
Recommendation |
---|---|---|---|
Multiple-Accumulate ( MULTIACCUM ) |
Faint targets. Large dynamic range. Optimal image construction. Ground processing of cosmic rays and saturation. |
Multiple non-destructive readouts at specific times during an integration. 0.215 < t < 8590 seconds. Number of readouts ![]() |
Recommended for most programs. Ensures the highest dynamic range. Most effective for correction of cosmic ray hits and saturation. |
Accumulate ( ACCUM ) |
Simplest observing mode. Produces a single image. |
t > 0.57 seconds. |
MULTIACCUM mode is preferred. |
Onboard Acquisition ( ACQ ) |
For coronagraphy only. Locate brightest source in a subarray and reposition telescope to place source in coronagraphic hole. |
ACCUM exposures are obtained, combined with cosmic ray rejection, hole located, sources located and centered. |
Reasonably bright sources in uncrowded fields. See Chapter 5 for more details. |
Bright Object ( BRIGHTOBJ ) |
For coronagraphic acquisition of bright targets which would saturate the arrays in the other modes with the shortest integration time allowed. |
reset/read/wait/read each pixel sequentially in a quadrant. 0.001024 < t < 0.2 seconds. |
When possible use a narrow filter with MULTIACCUM instead. |
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The |
NICMOS does not have a physical shutter mechanism. Instead, the following sequence of operations are performed to obtain an exposure:
Space Telescope Science Institute http://www.stsci.edu Voice: (410) 338-1082 help@stsci.edu |