Phase 2 Proposal Instructions for Cycle 10

10.3 Mode = ACQ/PEAK
Config = STIS/CCD

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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 directions, respectively. For more information, including when peak-ups are required, see the STIS Instrument Handbook.

Mode ACQ/PEAK should always be preceded by an ACQuisition.

10.3.1 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.

The apertures in Table10.4: Supported STIS Apertures are allowed.

A peak-down on the target intensity will automatically be performed on the occulting bar apertures 52X0.2F1.

A peak-up 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 ÐR appended to it should be used. Such exposures will peak up on a reference point offset from the occulting bar along the slitÕs length.

10.3.2 Spectral Element

See Table10.1: Supported Optional Parameters for STIS Instrument Modes.

10.3.3 Optional Parameters

See Table10.1: Supported Optional Parameters for STIS Instrument Modes for a listing by operating mode of all Optional Parameters. Here are descriptions for those Optional Parameters for ACQ/PEAK mode.

SIZEAXIS2
=DEF (default); 30Ð1022 (pixels, dispersive elements), 16Ð1022 (pixels, MIRROR)

Specifies the size of a CCD subarray in detector coordinates along the AXIS2 (cross-dispersion) 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.

10.3.4 Number of Iterations

The Number_Of_Iterations must be 1 in this Mode.

10.3.5 Time Per Exposure

The procedures to determine the exposure time for the ACQ/PEAK exposure are given in the STIS Instrument Handbook.

10.3.6 Special Requirements

None.