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HST Cycle 25 Phase II Proposal Instructions > Chapter 9: Space Telescope Imaging Spectrograph (STIS) > 9.3 Mode = ACQ/PEAKConfig = STIS/CCD

9.3
Mode = ACQ/PEAK
Config = STIS/CCD
In ACQ/PEAK Mode, a series of exposures is taken at several HST pointings offset along the detector axes, and the HST is repositioned to maximize (peak up) or minimize (peak down) the light intensity within a default or proposer-specified detector subarray. AXIS1 and AXIS2 are in the dispersion and cross-dispersion (or spatial) directions respectively. For more information, including when peakups are required, see the STIS Instrument Handbook.
Mode ACQ/PEAK should always be preceded by an ACQuisition.
9.3.1 Aperture or FOV
The aperture used for the ACQ/PEAK exposure will generally be identical to the aperture used for the subsequent ACCUM science exposure. For maximum centering accuracy, a peakup aperture smaller than the science exposure may be chosen. Peakups are required whenever an aperture dimension is less than or equal to 0.1 arcsec. Two peakups are recommended for the 0.1X0.03 aperture: one with the 0.2X0.09 aperture followed by another with the 0.1X0.03 aperture.
See Table 9.5 for the allowed ACQ/PEAK apertures. Note that you cannot perform a peakup with an E2 aperture (i.e. 52X... apertures ending with the E2 suffix), which are designed for use in conjunction with CCD Fringe Flats. If you need an ACQ/PEAK exposure prior to using an E2 aperture, perform the peakup using the 52X0.1E1 aperture. Then select the appropriate E2 aperture for the following science exposures.
When an ACQ/PEAK exposure using the occulting bar aperture 52X0.2F1 is specified, a peakdown rather than a peakup will automatically be performed.
A peakup will be performed otherwise. To peak up on the width of a slit with an occulting bar before peaking down on the bar itself, the occulting bar aperture name with –R appended to it should be used. Such exposures will peak up on a reference point offset from the occulting bar along the slit’s length.
9.3.2 Spectral Element
See Table 9.1, Supported Optional Parameters for STIS Instrument Modes.
9.3.3 Optional Parameters
See Table 9.1 for a listing by operating mode of all Optional Parameters. Here are descriptions for those Optional Parameters for ACQ/PEAK mode.
SIZEAXIS2
=DEF
(default); 30–1022 (pixels, dispersive elements), 16–1022 (pixels, MIRROR)
Specifies the size of a CCD subarray in detector coordinates along the AXIS2 (cross-dispersion or spatial) direction.
The default subarray with SIZEAXIS2=DEF depends on the aperture and spectral element. With the MIRROR element, the default subarray will generally be 32x32 CCD pixels centered on the aperture. However, the F1 fiducial slits use a 32x64 subarray. A subarray of 16x16 is also allowed when MIRROR is used.
With a first-order CCD grating (G230LB, G230MB, G430L, G430M, G750L, G750M), the default subarray will generally be 1022 x 32 CCD pixels. However, the F1 fiducial slits use a 1022 x 64 subarray.These subarrays have been chosen to minimize cosmic ray perturbations on the acquisition process.
9.3.4 Number of Iterations
The Number_of_Iterations must be 1 in this Mode.
9.3.5 Time Per Exposure
The procedures to determine the exposure time for the ACQ/PEAK exposure are given in the STIS Instrument Handbook.
9.3.6 Special Requirements
None.

HST Cycle 25 Phase II Proposal Instructions > Chapter 9: Space Telescope Imaging Spectrograph (STIS) > 9.3 Mode = ACQ/PEAKConfig = STIS/CCD

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