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Space Telescope Imaging Spectrograph




DESCRIPTION: This purpose of this activity is to measure the baseline performance and commandability of the CCD subsystem. This test assesses several CCD functions and performance characteristics, including: bias levels, read noise, dark current, CTE, and gain. Bias, dark, and flat field exposures are executed to achieve these goals. Full frame and binned (2 x 1, 1 x 2, and 2 x 2) observations are made. Biases are taken at gain=1 and read-out in subarray mode to support target acquisition and peakup modes. Only the primary amplifier (Amp D) is used. Dark exposures are made outside the SAA (as is standard). All exposures are internals

The visit structure outlined below has been constructed by filling the full orbit with internal exposures.

Visits 1 and 2 acquire bias frames and flats at the four commandable gain settings,1, 2, 4, and 8 e/DN. At the available gain settings (gain=2,8) 31 bias frames are acquired for construction of a superbias with negligible readout noise. At the supported gain settings (gain=1,4) only 21 bias frames are acquired since the remaining frames necessary for construction of a superbias will be acquired as part of the Cycle 17 bias monitoring program. A pair of flats is acquired in camera mode at two signal levels (achieved by using the 50CCD and F25ND3 apertures) at each gain setting. The flats will be analyzed to (1) provide a rough confirmation of the nominal gain calibration and (2) determine if there have been changes in the number or position of cosmetic artifacts, such as the shadows of particles on the detector window.

Bias and internal lamp exposures are obtained for binned modes, with binning factors of 2 x 1, 1 x 2, and 2 x 2, for evaluation of read noise, bias level, and gain of the binned settings

Biases are acquired using a 100x100 and 1024x32 subarray readout (and gain=4) in support of downstream target acquisitions and peakups.

Visit 3 acquires dark frames and bias frames for evaluation of the mean dark current at the operating temperature of the CCD and the identification of hot pixels.

Visit 4 acquires spectral flat field data at three different signal levels, spanning a factor of 100 in signal intensity, for evaluation of charge transfer efficiency through the edge response method. In addition 29 biases are taken at gain=1 to enable the construction of superbiases for each of the binned settings used in visit 2.


DEPENDENCIES: Should be executed after the initial CCD anneal (STIS-05)

DURATION: 4 fully packed orbits (Internals) If this activity was planned for occultation periods, it would require 12 orbits of ~1800 seconds duration each. This activity is a precursor to all other STIS CCD activities.


ANALYSES & EXPECTED RESULTS: Provides baseline measurements of CCD bias levels, gains, read noise, charge transfer efficiency, dark current levels, and performance verification of binning and subarray readpout capabilities. Provides a rough assessment of changes in flat field features due to dust motes or other particulates. Numerous bias frames are taken to permit construction of "super bias" frames in which the effects of read noise have been rendered negligible

This activity should execute after the STIS CCD anneal activity (STIS-05) and prior to other activities using the STIS CCD.


AUTHOR/telephone/email: Mary Elizabeth Kaiser/401-516-5088/

DATE: September 28, 2007