STScI Logo

Hubble Space Telescope
ACS TIRs

2013

ACS/WFC Amplifier D Read Noise Anomaly: Sudden Jump from 3.8 to 5.0 Electrons (ACS TIR 13-02)

The read noise in the quadrant of the ACS/WFC detector read out by amplifier D rose suddenly from 3.8 to 5.0 electrons RMS on January 20, 2013. For the following month until the next CCD anneal, this read noise fluctuated between 4.5 and 5.0 electrons until settling at 5.0. This new value is comparable to pre­-SM4 read noise levels (March 2002 — January 2007) and does not significantly affect most observations that are sky background limited. We measure no significant variation in the amplifier gain and verify that photometry has been stable over this time period. Only the amplifier D quadrant was affected. This anomaly does not appear to be related to the ASIC installed during SM4. A similar read noise jump occurred in ACS/WFC amplifier A on June 29, 2003. Both events were likely due to cosmic rays impacting the amplifiers on the detector.
Dan Coe, Norman Grogin, David Golimowski, Sara Ogaz, Roberto J. Avila 31 Dec 2013

2008

ACS-R Multi-Parameter Optimization Constraints (TIR 08-04

Abstract The repaired ACS WFC will undergo a three-week Optimization Campaign during early SMOV with read noise being the primary target for improvements through testing adjustments of a large number of detector control, voltage and timing patterns. A large number of factors, in addition to read noise, contribute to the utility of science data from ACS WFC. In this TIR we enumerate several such factors including Charge Transfer Efficiency (CTE), Full Well Depth (FWD), Linearity, Cross talk, gain stability and bias drift. For each we quantify values that existed when WFC was last used in January 2007 and provide extrapolation that we believe would have existed with a continuously operable instrument to May 2009. For each factor we provide qualitative discussion of how changes would impact science in order to provide a framework for considering changes that may arise during the Optimization Campaign. In many cases, e.g. for CTE, significant deterioration of performance from nominal expectations as a result of changes during the optimization campaign would provide support for adjusting the optimization to lessen this, even at the cost of some increase of read noise.
R. L. Gilliland 03 Dec 2008

Delivery of a new ACS SBC throughput curve for Synphot (TIR 2008-002)

On November 12th, 2007 a new ACS SBC throughput curve was implemented in CDBS, OPUS and DADS. This new curve is an improved version and accounts for SBC red leak. The red leak portion is based on a spectrum of HD 209458 prepared by Paul Goudfrooij.
Boffi, F.R. 21 Apr 2008

2007

Revised Procedures for Creating Charts to Support MAMA Moving Target Bright Object Protection(ACS TIR 07-01)

We describe a revised set of procedures and software for creating finding charts and object catalogues which can be used to assess the risk to the STIS MAMA and ACS SBC detectors from bright blue objects in the vicinity of proposed planetary observations. These charts show the path of given planet, moon or comet across the background of stars, down to magnitude limit of the GSC2 digital sky survey plates. Associated object catalogues and color-magnitude diagrams are also produced showing which stars may violate bright object limits for the selected instrument mode.
Charles Proffit et. al. 11 Jun 2007

2006

Quantum Yield Correction for ACS/HRC and ETC implementation(ACS TIR 06-03)

In the ACS/HRC CCD a single UV photon may generate more than one photo-electron. We calculate the theoretical quantum yield and discuss the impact on the calculation of the S/N ratio for an observation in the UV. Without such correction the S/N can be overestimated up to ~18% in the F220W and ~26% at the bluest edge of PR200L. The implementation of the quantum yield correction in the ACS Exposure Time Calculator (ETC) is also described.
M. Sirianni, C. Pavlovsky 07 Nov 2006

The ACS Side-2 Switch: An Opportunity to Adjust the WFC CCD Temperature Setpoint (ACS TIR 06-02)

This TIR describes the rationale for the WFC CCD temperature setpoint change from -77C to -81C that occurred concurrent with the switchover to Side 2 electronics in July 2006.
M. Sirianni, R. Gilliland, K. Sembach 06 Sep 2006

2004

Revision of the Advanced Camera for Surveys Filter Throughputs

Filter Throughput revision
F.R.Boffi 01 Jul 2004

2001

Scatter from the ACS/WFC inter-chip gap

A brief investigation was made to assess the scatter properties of the gap between the two WFC chips. The geometry of this gap is complex and composed of materials, which present diffusive surfaces that might potentially scatter light in an undesired fashion. Nevertheless, this gap could provide a useful dump for the unwanted light from a bright point source in a field of fainter sources under study, minimizing the area of the image affected by blooming (along the CCD columns).
George Hartig 27 May 2003

Related TIRs from the Telescopes Branch

2013

ACS/WFC Amplifier D Read Noise Anomaly: Sudden Jump from 3.8 to 5.0 Electrons (ACS TIR 13-02)

The read noise in the quadrant of the ACS/WFC detector read out by amplifier D rose suddenly from 3.8 to 5.0 electrons RMS on January 20, 2013. For the following month until the next CCD anneal, this read noise fluctuated between 4.5 and 5.0 electrons until settling at 5.0. This new value is comparable to pre­-SM4 read noise levels (March 2002 — January 2007) and does not significantly affect most observations that are sky background limited. We measure no significant variation in the amplifier gain and verify that photometry has been stable over this time period. Only the amplifier D quadrant was affected. This anomaly does not appear to be related to the ASIC installed during SM4. A similar read noise jump occurred in ACS/WFC amplifier A on June 29, 2003. Both events were likely due to cosmic rays impacting the amplifiers on the detector.
Dan Coe, Norman Grogin, David Golimowski, Sara Ogaz, Roberto J. Avila 31 Dec 2013

2008

ACS-R Multi-Parameter Optimization Constraints (TIR 08-04

Abstract The repaired ACS WFC will undergo a three-week Optimization Campaign during early SMOV with read noise being the primary target for improvements through testing adjustments of a large number of detector control, voltage and timing patterns. A large number of factors, in addition to read noise, contribute to the utility of science data from ACS WFC. In this TIR we enumerate several such factors including Charge Transfer Efficiency (CTE), Full Well Depth (FWD), Linearity, Cross talk, gain stability and bias drift. For each we quantify values that existed when WFC was last used in January 2007 and provide extrapolation that we believe would have existed with a continuously operable instrument to May 2009. For each factor we provide qualitative discussion of how changes would impact science in order to provide a framework for considering changes that may arise during the Optimization Campaign. In many cases, e.g. for CTE, significant deterioration of performance from nominal expectations as a result of changes during the optimization campaign would provide support for adjusting the optimization to lessen this, even at the cost of some increase of read noise.
R. L. Gilliland 03 Dec 2008

Delivery of a new ACS SBC throughput curve for Synphot (TIR 2008-002)

On November 12th, 2007 a new ACS SBC throughput curve was implemented in CDBS, OPUS and DADS. This new curve is an improved version and accounts for SBC red leak. The red leak portion is based on a spectrum of HD 209458 prepared by Paul Goudfrooij.
Boffi, F.R. 21 Apr 2008

2007

Revised Procedures for Creating Charts to Support MAMA Moving Target Bright Object Protection(ACS TIR 07-01)

We describe a revised set of procedures and software for creating finding charts and object catalogues which can be used to assess the risk to the STIS MAMA and ACS SBC detectors from bright blue objects in the vicinity of proposed planetary observations. These charts show the path of given planet, moon or comet across the background of stars, down to magnitude limit of the GSC2 digital sky survey plates. Associated object catalogues and color-magnitude diagrams are also produced showing which stars may violate bright object limits for the selected instrument mode.
Charles Proffit et. al. 11 Jun 2007

2006

Quantum Yield Correction for ACS/HRC and ETC implementation(ACS TIR 06-03)

In the ACS/HRC CCD a single UV photon may generate more than one photo-electron. We calculate the theoretical quantum yield and discuss the impact on the calculation of the S/N ratio for an observation in the UV. Without such correction the S/N can be overestimated up to ~18% in the F220W and ~26% at the bluest edge of PR200L. The implementation of the quantum yield correction in the ACS Exposure Time Calculator (ETC) is also described.
M. Sirianni, C. Pavlovsky 07 Nov 2006

The ACS Side-2 Switch: An Opportunity to Adjust the WFC CCD Temperature Setpoint (ACS TIR 06-02)

This TIR describes the rationale for the WFC CCD temperature setpoint change from -77C to -81C that occurred concurrent with the switchover to Side 2 electronics in July 2006.
M. Sirianni, R. Gilliland, K. Sembach 06 Sep 2006

2004

Revision of the Advanced Camera for Surveys Filter Throughputs

Filter Throughput revision
F.R.Boffi 01 Jul 2004

2001

Scatter from the ACS/WFC inter-chip gap

A brief investigation was made to assess the scatter properties of the gap between the two WFC chips. The geometry of this gap is complex and composed of materials, which present diffusive surfaces that might potentially scatter light in an undesired fashion. Nevertheless, this gap could provide a useful dump for the unwanted light from a bright point source in a field of fainter sources under study, minimizing the area of the image affected by blooming (along the CCD columns).
George Hartig 27 May 2003