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HST Cycle 25 Phase II Proposal Instructions > Chapter 9: Space Telescope Imaging Spectrograph (STIS) > 9.6 Mode = TIME–TAGConfig = STIS/FUV–MAMA,Config = STIS/NUV–MAMA

9.6
Mode = TIME–TAG
Config = STIS/FUV–MAMA,
Config = STIS/NUV–MAMA
TIME–TAG Mode is used for imaging and spectroscopy with high time resolution. When used in TIME–TAG Mode, the MAMA produces an event stream with a time resolution of 125 microseconds. If the incoming event rate exceeds about 770,000 counts per second, not all events get registered due to finite electronic response time. The AXIS1 and AXIS2 half-pixel coordinates (11 bits each) of each photon event, along with 9 bits of fine-resolution time data, are stored as a 32-bit word in data buffer memory. See the discussion of TIME–TAG Mode in the STIS Instrument Handbook.
9.6.1 Aperture or FOV
See Table 9.5, Supported STIS Apertures.
9.6.2 Spectral Element
See Table 9.1, Supported Optional Parameters for STIS Instrument Modes.
9.6.3 Wavelength
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.
 
No wavelength should be specified if the MIRROR is the spectral element.
9.6.4 Optional Parameters
See Table 9.1 for a listing by operating mode of all Optional Parameters. Here are descriptions for those Optional Parameters for MAMA TIME-TAG mode.
BUFFER– TIME
=40 or greater (integer seconds)
This required parameter should be equal to or less than the time to fill half the STIS buffer (2 x 106 photon events) during a TIME–TAG exposure.
If the predicted total number of events from a TIME–TAG exposure exceeds the STIS data buffer capacity of 4 x 106 photon events, data must be transferred to the HST onboard science data recorder during the exposure. Transfers of data from the STIS buffer during an exposure will be made in 8-MByte blocks (half the buffer capacity). The value of BUFFER–TIME should be equal to or less than the half-buffer capacity (2 x 106 counts) divided by the estimated maximum average count rate in photons per second (see the STIS Instrument Handbook). If the actual count rate is less than expected and fewer than 2 x 106 counts are received during this time, the 8-MByte blocks will contain fill data.
Note that BUFFER–TIME should include expected counts from the detector dark current as well as the detected photon events, factoring in the instrument quantum efficiency. A conservative value of BUFFER–TIME is recommended (err slightly on the low side) to avoid data loss. For more details, see the STIS Instrument Handbook.
WAVECAL=NO
Turns off the automatic scheduling of wavelength calibration exposures for external spectroscopic science exposures. A value of WAVECAL=NO will disable the automatic wavelength calibrations for the entire visit. If WAVECAL=NO is specified, the following rules will apply:
At least one target=WAVE exposure must be added in every block of exposures with the same spectral element and central wavelength. For a list of all allowed aperture/wavelength combinations, go to:
http://www.stsci.edu/hst/stis/proposing/phase2/
go_wavecal_apertures.html.
At least one TARGET=WAVE exposure must be added before and/or after the science exposure(s) or CCDFLAT exposure.
No more than 60 minutes may elapse between any science exposure and a corresponding WAVE exposure. Aperture selection must be the same as would have been selected for an automatic wavelength calibration exposure. Exposure time must be specified as "Default Time".
9.6.5 Number of Iterations and Time Per Exposure
Number_of_Iterations must be 1 in this mode.
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. Enter the total time of data collection as Time_Per_Exposure. An exposure time of less than 0.1 sec will be set to the minimum MAMA exposure time of 0.1 second. The maximum permissible Time_Per_Exposure for this mode is 6553.5 seconds.
If BUFFER–TIME < 99 seconds, photon events will be generated faster than data can be transferred out of the buffer during the exposure. In this case, Time_Per_Exposure should be less than or equal to 2 * BUFFER–TIME so that the exposure can complete before data transfer is necessary. A BUFFER–TIME of 99 seconds corresponds to a maximum average count rate of 20,200 counts/sec.
Note that TIME–TAG exposures have the potential to rapidly use up the HST onboard storage capacity. Caution is advised on any exposure with an exposure time greater than 30 * BUFFER–TIME, which corresponds to 6 x 107 counts, or about 2 GBits (close to 20% of the solid-state recorder capacity). Please see the STIS Instrument Handbook.
9.6.6 Special Requirements
The special requirements RT ANALYSIS and PARallel WITH are not permitted on TIME–TAG Mode exposures.

HST Cycle 25 Phase II Proposal Instructions > Chapter 9: Space Telescope Imaging Spectrograph (STIS) > 9.6 Mode = TIME–TAGConfig = STIS/FUV–MAMA,Config = STIS/NUV–MAMA

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