This mode requests the NICMOS flight software to locate the brightest target in the acquisition aperture of camera 2 (one quarter of the full
NIC2 FOV, or 9.6x 9.6 arcsec) and place it behind the coronagraphic spot of camera 2. It is only necessary as a preparation for coronagraphy with the
NIC2-CORON aperture. Two images will be taken and downlinked, each with a single non-destructive readout at the beginning and the end of the exposure. Two each of background and lamp-on exposures will be taken to locate the coronagraphic hole.
The NIC2–ACQ aperture must be used in this Mode.
The Wavelength parameter is not required for NICMOS observations and should be left blank.
Always enter 1. However, two exposures of the duration given in
Time_Per_Exposure will be executed, for purposes of onboard cosmic ray elimination by the NICMOS flight software.
Exposure times in ACQ Mode are quantized. The exposure consists of an initial readout, followed by a period of data accumulation, followed by a final readout. The
Time_Per_Exposure (in seconds) refers to the total integration time, which begins at the start of the initial readout and ends at the start of the final readout. The NICMOS Timing Pattern Generator (TPG) uses a list of discrete values for the time
between readouts (
TPG_TIME), which is given in
Table 12.3: Quantized Legal NICMOS TPG Expose Times. The specified exposure time should be one of a set of possible values allowed by the following formula:
If the exposure time entered by the user is not one of the values allowed by the above formula, it will be reduced to the next lowest legal value. It is illegal to specify an exposure time below the minimum of 0.228 seconds.
Science exposures associated with this acquisition must be identified as part of the <exposure–list> and must use the
NIC2 configuration and the coronagraphic aperture
NIC2–CORON.
The Special Requirement PARallel
WITH is not allowed in this Mode.
