2.6 SBC Considerations

It is essential that observers proposing to use the SBC review and abide by the procedures and rules described in Section 4.6 and Section 7.2. Designing safe observing programs will protect the MAMA detectors in the SBC from being permanently damaged by over-illumination. We therefore ask all users to share the responsibility of STScI to ensure the safety of the MAMA detectors. All proposed SBC targets and fields must be discussed in the Phase I proposal, so that their feasibility can be assessed by the TAC and STScI.

In 2019, the zeropoints for the SBC were updated to correct a long-standing ~30% discrepancy in the absolute flux calibration of the imaging modes. The error was found to be caused by inaccuracies in the filter and detector throughput tables used to derive the SBC zeropoints. The discrepancy is such that the SBC is actually ~30% more sensitive than previously estimated: a source of a given astronomical flux produces a ~30% larger SBC count-rate. Conversely, prior conversions of observed SBC count-rate to flux have overestimated the astronomical flux by ~30%. The throughput tables have now been corrected, and new zeropoints have been derived for the relevant imaging modes. Details are provided in ACS ISR 2019-05.

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ACS Instrument Handbook
- • Acknowledgments
- • Change Log
- • Chapter 1: Introduction
- Chapter 2: Considerations and Changes After SM4
  - • 2.1 SM4 Repair of ACS
  - • 2.2 Comparison of WFC and UVIS
  - • 2.3 Comparison of HRC and UVIS
  - • 2.4 Dithering Considerations
  - • 2.5 CTE Considerations
  - • 2.6 SBC Considerations
- Chapter 3: ACS Capabilities, Design and Operations
  - • 3.1 ACS Location in the HST Focal Plane
  - • 3.2 Instrument Capabilities
  - • 3.3 Instrument Design
  - • 3.4 Basic Instrument Operations
  - • 3.5 ACS Quick Reference Guide
- Chapter 4: Detector Performance
  - • 4.1 Overview
  - • 4.2 The CCDs
  - • 4.3 CCD Operations and Limitations
  - • 4.4 The SBC MAMA
  - • 4.5 SBC Operations and Limitations
  - • 4.6 SBC Bright-Object Limits
- Chapter 5: Imaging
- Chapter 6: Polarimetry, Coronagraphy, Prism and Grism Spectroscopy
  - • 6.1 Polarimetry
  - • 6.2 Coronagraphy
  - • 6.3 Grism and Prism Spectroscopy
- Chapter 7: Observing Techniques
  - • 7.1 Designing an ACS Observing Proposal
  - • 7.2 SBC Bright Object Protection
  - • 7.3 Operating Modes
  - • 7.4 Patterns and Dithering
  - • 7.5 A Road Map for Optimizing Observations
  - • 7.6 CCD Gain Selection
  - • 7.7 ACS Apertures
  - • 7.8 Specifying Orientation on the Sky
  - • 7.9 Parallel Observations
  - • 7.10 Pointing Stability for Moving Targets
- Chapter 8: Overheads and Orbit-Time Determination
  - • 8.1 Overview
  - • 8.2 ACS Exposure Overheads
  - • 8.3 Orbit Use Determination Examples
- Chapter 9: Exposure-Time Calculations
  - • 9.1 Overview
  - • 9.2 Determining Count Rates from Sensitivities
  - • 9.3 Computing Exposure Times
  - • 9.4 Detector and Sky Backgrounds
  - • 9.5 Extinction Correction
  - • 9.6 Exposure-Time Examples
  - • 9.7 Tabular Sky Backgrounds
- Chapter 10: Imaging Reference Material
  - • 10.1 Introduction
  - • 10.2 Using the Information in this Chapter
  - 10.3 Throughputs and Correction Tables
    - • WFC F435W
    - • WFC F475W
    - • WFC F502N
    - • WFC F550M
    - • WFC F555W
    - • WFC F606W
    - • WFC F625W
    - • WFC F658N
    - • WFC F660N
    - • WFC F775W
    - • WFC F814W
    - • WFC F850LP
    - • WFC G800L
    - • WFC CLEAR
    - • HRC F220W
    - • HRC F250W
    - • HRC F330W
    - • HRC F344N
    - • HRC F435W
    - • HRC F475W
    - • HRC F502N
    - • HRC F550M
    - • HRC F555W
    - • HRC F606W
    - • HRC F625W
    - • HRC F658N
    - • HRC F660N
    - • HRC F775W
    - • HRC F814W
    - • HRC F850LP
    - • HRC F892N
    - • HRC G800L
    - • HRC PR200L
    - • HRC CLEAR
    - • SBC F115LP
    - • SBC F122M
    - • SBC F125LP
    - • SBC F140LP
    - • SBC F150LP
    - • SBC F165LP
    - • SBC PR110L
    - • SBC PR130L
  - • 10.4 Geometric Distortion in ACS
- • Glossary

2.6 SBC Considerations

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