The two MAMAs are photon-counting detectors that provide a two-dimensional ultraviolet capability. ACCUM Mode should be used for all observations that do not require time resolution on scales of minutes or less. Dispersion (in spectroscopic modes) runs along
AXIS1; the spatial direction of the slit (cross-dispersion) is along
AXIS2.
There are 1024 x 1024 physical pixels in the MAMA array, but each physical pixel is sampled by three electrodes, allowing centroiding of electron clouds to half-pixel accuracy. In ACCUM Mode, the MAMAs accumulate counts in the STIS data buffer as they are received, producing images with 2048 x 2048 “high-resolution” pixels with half physical pixel coordinates. Images can be binned either by the STIS flight software (using the
BINAXIS1 and
BINAXIS2 optional parameters described below) or on the ground, to produce images with 1024 x 1024 physical pixels. All optional parameters are specified in physical pixel coordinates. For a more detailed description, see the discussion of MAMA
ACCUM mode in the
STIS Instrument Handbook.
Enter the value of the central wavelength in Angstroms. Table 9.2 gives the allowed values of the central wavelength for each spectroscopic spectral element. Consult the
STIS Instrument Handbook for the associated minimum and maximum wavelength and other information pertaining to the spectroscopic elements.
See Table 9.1 for a listing by operating mode of all Optional Parameters. Here are descriptions for those Optional Parameters for
MAMA ACCUM mode.
These parameters specify whether onboard rebinning is to be performed on the accumulated image in memory after the exposure is completed. MAMA photon events are stored in memory in half-pixel coordinates (high-resolution pixels). This rebinning is a summation of two high-resolution pixels in the AXIS1 or dispersion (
BINAXIS1) and the
AXIS2 or cross dispersion (
BINAXIS2) directions to values corresponding to the physical pixels of the detector. The default values for all spectral elements and apertures are not to rebin in either direction, resulting in four high-resolution pixel values for each physical pixel.
Enter the number of times (Number_of_Iterations) this exposure should be iterated, and the exposure time (
Time_Per_Exposure) per iteration.
If Number_of_Iterations > 1 is specified with a pattern, the pattern is executed once with the specified number of iterations being taken at each point in the pattern. If no pattern is specified, the specified number of iterations will be taken at the single pointing.
Time_Per_Exposure must be an integral multiple of 0.1 second. If it is not its value will be truncated down to the next lower integral multiple of 0.1 sec. If the exposure time is less than 0.1 sec, it will be set to the MAMA minimum value of 0.l sec. The maximum permissible
Time_Per_Exposure for this mode is 6553.5 seconds.
