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Space Telescope Imaging Spectrograph

ACTIVITY TITLE: CCD Spectroscopic Throughputs



DESCRIPTION: This activity has two functions: Determination of the STIS sensitivity for the CCD spectroscopic modes and verification of the CTE correction at high signal levels. It also provides a measure of the resolution in the spatial direction at two positions along the slit for each CCD spectroscopic mode.

Confirmation of STIS sensitivity for CCD spectroscopic modes: Obtain exposures in each of the 3 low-resolution CCD spectroscopic modes (G230LB, G430L, and G750L) to establish the post-SM4 STIS baseline sensitivity. The sensitivity is monitored at the nominal (central) target position along the 52X2 slit and at the E1 position, which is closer to the location of Amp D, the default CCD amplifier. Thus, fewer parallel shifts are required and CTI effects are mitigated. The sensitivity of the medium resolution CCD modes (G230MB, G430M, G750M) is also checked at the nominal and E1 slit positions for two grating settings for each mode.

This activity resumes sensitivity monitoring of each CCD spectroscopic mode to enable detection of any change due to contamination or other causes. The duty cycle for monitoring the sensitivity of the low resolution spectroscopic modes is once every 1.5 months, and once per year for each of the 3 medium resolution modes. The same high-declination calibration standard (AGK+81D266) is used throughout the program.

Verification of the CTE correction at high signal levels: CTI is a function of signal level. In this activity, the target is stepped along the slit (52X2) in mode G430L and the flux is measured at 7 positions to verify CTE correction at high flux levels.


DEPENDENCIES: Execute after the CCD Image quality and target acquisition activity (STIS-13). This activity uses an external target and may need to execute after the end of the BEA period.

DURATION: 3 orbits (external).


ANALYSES & EXPECTED RESULTS: This activity will provide a broad range of basic performance information. The absolute sensitivity of STIS will be measured for two positions along the slit for the 3 low resolution spectroscopic modes and at two grating positions (central wavelengths) for each of the 3 medium resolution modes. Ratioing the results for each mode with the last Cycle 12 sensitivity measurements will provide a measurement of the environment over the past several years and establish the current baseline for contamination monitoring and trending instrument sensitivity. The resolution in the spatial direction is obtained at two spatial positions for each mode. The G430L spectra acquired at multiple slit positions will be analyzed using the methodology laid out in ISR STIS 2006-03 (Goudfrooij and Bohlin, 2006) to assess the CTI dependence on high signal levels. The algorithm discussed therein has been incorporated into the CalSTIS pipeline.

Results of this activity will be used to refine exposure times for Cy 17 observations if necessary.

COMMENTS: This activity comprises the first visit of the nominal Cycle 17 CCD Spectroscopic Sensitivity Monitoring program, establishes the baseline for the Medium Resolution Spectroscopic Sensitivity Monitor that is executed annually, and executes the Cycle 17 observations for verification of the CTI correction at high signal levels. This activity may be regarded as part of the Cycle 17 calibration program. The low-resolution CCD spectroscopic modes are monitored once every 1.5 months.

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

DATE: September 25, 2007