17.10 SM4 and SMOV4 Calibration

After the successful repair of STIS during Servicing Mission 4 (SM4), a plan for verification and preliminary calibration was executed during the subsequent period of Servicing Mission Observatory Verification (SMOV4). The SMOV4 plan for STIS focused on ensuring that observers can obtain data of sufficient quality to meet their scientific goals, but some of the more time consuming calibration observations that do not affect the planning of observations and which can be applied retroactively, (e.g., high signal-to-noise pixel-to-pixel flats and high precision sensitivity determinations for all central wavelength settings), were deferred and included in the Cycle 17 calibration plan. As a result the initial calibration precision for STIS data products delivered early in Cycle 17 is less than that which will ultimately be obtainable when the final calibration reference files become available for those observations. Significant updates to the calibration will be announced on the STIS webpages.
 
A summary of preliminary STIS SMOV4 activities follows.

STIS-01: Modes and Data Interface Checks

• Includes turn-on and telemetry checks that verify the capability to enter required instrument and detector states during normal operations.
• Includes the initial turn-on of the MAMA low voltage (LV) and checks of the MAMA readout electronics that can be made with the high voltage (HV) off.
  
• Includes the initial turn-on of the CCD thermal electric cooler (TEC).
  

STIS-02: Memory Load and Dump

• Loads, dumps and compares sections of memory with stored images to verify operations.

STIS-03: Science Data Buffer Check with Self-Test

• Loads a test pattern into the science data buffer. The buffer contents are subsequently examined using memory and exposure dumps.

STIS-04: Mechanism Mini-Functional

• Initializes all mechanisms, except the focus and corrector mechanism, commands them to selected positions, and moves them over the full range necessary for normal operations. Commanded motions are verified using telemetry.

STIS-05: CCD Anneal

• The CCD is warmed from ~ -80C to ~ +5C to repair hot pixels. A series of darks and biases are taken to monitor and evaluate CCD performance before and after the anneal process.

STIS-06: CCD Functional

• Bias, dark, and tungsten lamp exposures are taken, using various gains and binning, to measure the baseline CCD performance.

STIS-07: CCD Bias and Dark Monitor

• Acquisition of sufficient dark and bias frames to permit construction of superbias and superdark frames needed for pipeline image reduction.

STIS-08: Aperture Wheel and Lamp Functional Tests

• Aperture positions are checked using tungsten lamp images through several slits.
• Thermal drifts are measured using repeated observations of the 0.2X0.2 aperture interspersed throughout the test.
  
• Pt/Cr-Ne lamp functionality is checked by obtaining images with the HITM1, HITM2, and LINE lamps.

STIS-09: STIS to FGS Alignment

• Target positioning accuracy in the STIS aperture plane using fine guidance sensors (FGS) guiding is measured using star field and lamp images illuminating the 50CCD aperture.

STIS-10: CCD Optical Format Verification

• Measurement of the location of the CCD spectra and images on the detector for each CCD spectral element (G230LB, G230MB, G430L, G430M, G750M, G750) and MIRVIS using the HITM calibration lamps.

STIS-11: External Focus Check

• Evaluation of the STIS PSF at the aperture plane using small slit (0.1X0.09) ACQ/PEAK images and point source images with the F28X50OII filter.
• Determination of the shape of the PSF at ultraviolet (UV) wavelengths from spectra acquired using the G230LB grating.
• Estimation of the STIS focus through comparison of the aperture throughputs and PSF shape with previous values.

STIS-12: Corrector and Focus Alignment

• Coarse and/or fine adjustments of the STIS focus are made if STIS-11 finds a significantly degraded PSF. If a focus adjustment is necessary, then the STIS CM1 mirror will be adjusted in tip/tilt and focus to optimize the PSF. Coarse adjustments optimize the encircled energy of an isolated star observed through the 50CCD aperture while fine adjustment sweeps optimize the small aperture throughputs.

STIS-13: CCD Spectroscopic Image Quality and ACQ Tests

• Checks the cross dispersion PSF using point source spectra obtained at multiple positions along a long slit.
• Peak-ups are executed to check target centering at the E1 slit location.

STIS-14: CCD CTE Check

• Lamp exposures are taken at multiple positions along the 0.05X31ND slit, and read-out using amplifiers D and B, to search for, and compare, CTE losses as a function of Y-position on the detector.

STIS-15: CCD Spectroscopic Throughputs

• Determination of the throughput of each spectroscopic CCD mode from observations of the standard high-latitude sdO-type star AGK+81D266.

STIS-16: CCD Image and Pointing Stability

• The pointing stability is assessed after execution of a large pointing maneuver selected to apply a significant thermal change to STIS. Star field images and lamp images of an aperture are interspersed to measure the image stability at detector and aperture planes.

STIS-17: FUV-MAMA HV Recovery

• The FUV-MAMA voltage is ramped-up in stages while taking dark exposures and using on-board count rate monitors to protect against anomalies. Fold analysis is performed after it has been verified that the voltage can be safely ramped-up to the required level.

STIS-18: NUV-MAMA HV Recovery

• The NUV-MAMA voltage is ramped-up in stages while taking dark exposures and using on-board count rate monitors to protect against anomalies. A fold analysis is performed after it has been verified that the voltage can be safely ramped-up to the required level.

STIS-19: FUV-MAMA Dark Measure

• Characterization of the FUV-MAMA glow as a function of detector warm-up through the acquisition of a series of darks spanning the 5-orbit SAA-free period.

STIS-20: NUV Dark Monitor

• Monitoring of the NUV phosphorescent window glow to determine the equilibrium behavior and the onset of science observations.

STIS-21: FUV-MAMA Optical Format Verification

• Measurement of the location of the FUV spectra on the detector for each FUV-MAMA spectral element (G140L, G140M, E140M, and E140H) using the HITM calibration lamps.

STIS-22: NUV-MAMA Optical Format Verification

• Measurement of the location of the NUV spectra on the detector for each NUV-MAMA spectral element (G230L, G230M, E230M, E230H, and PRISM) using the HITM calibration lamps.

STIS-23: FUV-MAMA Image Quality

• Checks the cross dispersion PSF using point source spectra of G140L obtained at multiple positions along a long slit.

STIS-24: NUV-MAMA Image Quality

• Checks the cross dispersion PSF using point source spectra of G230L obtained at multiple positions along a long slit.

STIS-25: MAMA Spectroscopic Throughputs

• Determination of the throughput of each spectroscopic MAMA mode, except the NUV PRISM, from standard star observations (preferably GRW+70D5824, AGK+81D266, or BD+28D4211).

STIS-26: MAMA Image Stability

• The pointing stability is assessed after the execution of a large pointing maneuver selected to apply a significant thermal change to STIS. Repeated lamp images of an aperture are obtained to measure the image stability at detector over a two orbit period.