Phase 2 Proposal Instructions for Cycle 10

12.3 Mode = ACCUM
Configuration = ACS/HRC

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Photons are counted on the High Resolution Channel CCD as accumulated charge which is read out at the end of the exposure and converted to DN at a selectable gain. The DN are stored as 16-bit words in a data memory array. A full detector readout is 1062x1044 pixels, which includes 19 leading and 19 trailing pixels of overscan per line and 20 virtual overscan lines.

12.3.1 Aperture or FOV

Allowed apertures for this mode are:
HRC, HRC-FIX, HRC-OCCULT0.8, HRC-CORON1.8, HRC-CORON3.0, HRC-512, HRC-SUB1.8

HRC must be specified if spectral element PR200L is specified.

To ensure a consistent position of the coronographic mechanism for all ACCUM exposures using Apertures HRC-CORON1.8, HRC-CORON3.0 and HRC-SUB1.8, you should request such exposures and their ACQ Mode exposure(s) within a single visit (i.e., without interleaving exposures that use other Apertures)

Spectral Element

See Table12.3: Spectral Elements for use with ACS/WFC and ACS/HRC Configurationsa. Note: For HRC exposures using a polarizer, STScI will automatically apply corrections for small polarizer-induced shifts in the target position only when aperture HRC is specified.

12.3.2 Wavelength

If a ramp filter (any spectral element beginning with the letters �FR�) is specified, enter the value of the desired central wavelength in �ngstroms. Table12.4: Wavelength Ranges for the WFC/HRC Ramp Filters gives the allowed minimum and maximum wavelength for each ramp filter. Any HRC aperture may be used with the ramp filters.

Note: A wavelength should be not specified if a ramp filter is not being used.

12.3.3 Optional Parameters

CR-SPLIT
= 2 (default) - 8; NO

Specifies the number of sub-exposures into which the exposure is to be split for the purpose of cosmic ray elimination in post-observation data processing (see the ACS Instrument Handbook). The specified exposure time will be divided equally among the number of CR-SPLIT exposures requested. If CR-SPLIT=NO, the exposure is taken without splitting. If a pattern is also specified (see Chapter8:Pointings and Patterns), the specified number of sub-exposures will be taken at each pattern point. Every internal Exposure Specification will be taken as a single exposure (i.e., an implicit CR-SPLIT=NO). Thus the CR-SPLIT parameter is not permitted to be specified for internal exposures.

GAIN
= 2 (default), 4(e/DN)

Specifies the gain of the CCD electronics in e/DN.

SIZEAXIS2
= FULL (default); 16 - 1022 (pixels)

Specifies the size of an HRC subarray in detector coordinates along the AXIS2 direction. SIZEAXIS2 may not be specified if a subarray Aperture (HRC-512, HRC-SUB1.8) is specified.
The default value of FULL for SIZEAXIS2 will result in a full detector readout of 1062 x 1044 pixels. Subarrays will be centered at the reference position of the Aperture used for the exposure.

FLASHEXP
= NONE (default), SHORT, MID, LONGIndicates the duration of a post-exposure, pre-readout LED �flash.� A flash is used to ensure that CCD traps are filled, so that image photons are not lost to traps during readout. The default value of NONE means that there will be no flash. The SHORT, MID, and LONG choices select from three combinations of flash duration and flash current as defined by the ACS Calibration Team. They are intended for use in situations in which background is high, medium, and low, respectively. See the ACS Instrument Handbook for details and guidelines on the use of the post-flash capability.

12.3.4 Number of Iterations

Enter the number of times this Exposure Specification should be iterated, each with the specified Time_per_Exposure. Note: CR-SPLIT and multiple iterations are mutually exclusive capabilities. If Number_Of_Iterations > 1 on an external exposure, CR-SPLIT=NO must be specified.

12.3.5 Time Per Exposure

Enter the exposure time, in seconds, for the Exposure Specification. If Number_of_Iterations = 1, the Time_per_Exposure is divided equally among the CR-SPLIT copies, if any. If Number_of_Iterations > 1, each iteration comprises a single exposure whose duration is Time_per_Exposure.

Note that the exposure time for an individual HRC exposure, after any CR-SPLIT is applied, must be an integer multiple of 0.1 second and in the range of 0.1 to 3600 sec.

Time_per_Exposure must be 0 when the target is BIAS.