AAS 199th meeting, Washington, DC, January 2002
Session 8. Instruments for HST and NGST
Display, Monday, January 7, 2002, 9:20am-6:30pm, Exhibit Hall

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[8.03] STIS Status after the Switch to Side-2, Calibration and Time-Tag Fixes

J. E. Davies, T. M. Brown, P. Goudfrooij, C. Proffitt, K. C. Sahu, D. Stys, J. Valenti (STScI)

Since July 2001, STIS has been operating on its secondary (Side-2) electronics due to the failure of the primary (Side-1) system. The change to Side-2 has required new calibration work.

The dark rate of the STIS CCD varies after the switch to Side-2, as it depends on the temperature of the CCD which cannot be regulated precisely using Side-2 electronics. By tracking the CCD housing temperature, the relation of this dark rate to the housing temperature is found to be linear for pixels at a fixed dark rate, but the relation also depends (slightly) on the dark rate.

The STIS CCD read noise has increased by 1 electron/sec for all four amplifiers after the switch to Side-2. This increased read noise is due to electronic pick-up noise, unlike before when it was consistent with white noise. Work towards reducing or removing this pattern noise is ongoing.

The sensitivity of STIS in the imaging modes has been recalibrated and updated. This has also resulted in new aperature throughputs. Since the switch to Side-2, the sensitivity seems to have remained the same based on initial data.

MAMA TIME-TAG data retrieved from the archive prior to 13 Sep 2001 may contain erroneous temporal gaps and jumps, potentially affecting the flux calibration of extracted spectra. New archive software installed on 13 Sep 2001 fixes all known problems with TIME-TAG data.

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