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Hubble Space Telescope
Advanced Camera for Surveys

The Advanced Camera for Surveys (ACS) is a third-generation Hubble Space Telescope (HST) instrument. ACS was installed during HST servicing mission 3B. During servicing mission 4, the ACS WFC was repaired after an electronics malfunction in 2007.

ACS Utilities

ACS Zeropoint Calculator

This webtool is designed to provide users with an interface for computing time-dependent zeropoint information (e.g PHOTFLAM, STmag, VEGAmag, etc..). It uses the most recent component and throughput files to compute the zeropoints for all filters or one specified by the user. The results are displayed in an table and if an extraploation warning is raised by pysynphot, it is displayed beneath the table.

ACS CTE Correction Calculator

This webtool is designed to provide users with an interface for computing CTE corrections using the photometric CTE model described on the Photometric CTE Corrections webpage.

ACS CTE Forward Model

A Jupyter notebook is available to guide users in the proper usage of the CTE forward model. In fall of 2018, the capability to simulate the effects of CTE losses during readout on input images, i.e., adding the charge trails to images rather than correcting them, was added to CALACS. Called the ACS CTE forward model, this software is intended for users who wish to more fully understand the effects of the pixel-based CTE correction on their measurements by forward-modeling synthetic data (or other data unaffected by CTE losses) and then CTE-correcting it.

Late Breaking News

News Archive

28 Mar 2019 ISR 19-02 by T. D. Dejardins, "Post-SM4 ACS/WFC Bias I: The Read Noise History" is now posted

28 Feb 2019 ISR 19-01 by N. Hathi et al, "The ACS/WFC G800L Grism: I. Long-term Stability" is now posted

20 Dec 2018 ISR 18-09 by J. Ryon et al, "ACS/WFC Parallel CTE from EPER Tests" is now posted

26 Nov 2018 ISR 18-08 by A. Bellini et al, "Focus-diverse, empirical PSF models for the ACS/WFC" is now posted

26 Oct 2018 ISR 18-07 by R.J Avila et al, "Mitigating Elevated Dark Rates in SBC Imaging" is now posted

23 Oct 2018 ISR 18-06 by T.D Desjardins and N.A. Grogin, "Remeasuring the ACS/WFC Absolute Gains" is now posted

28 Sep 2018 ISR 18-05 by N.D. Miles et al, "Updates to the CALACS Cosmic Ray Rejection Routine: ACSREJ" is now posted

30 Aug 2018 ISR 18-04 by J. Anderson and J.E. Ryon, "Improving the Pixel-Base CTE-correction Model for ACS/WFC" is now posted

31 May 2018 ISR 18-03 by S. Hoffmann et al., "A Minor Contamination Event in May 2017 Affecting the ACS/WFC CCD's" is now posted

17 Apr 2018 ISR 17-09 by J. Mack et al, "ACS/WFC Sky Flats from Frontier Fields Imaging." is now posted

29 Mar 2018 ISR 18-02 by N.D. Miles, "Updates to Post-Flash Calibration for the Advanced Camera for Surveys Wide Field Channel" is now posted.

16 Mar 2018 ISR 17-10 by S.E. Deustua and J. Mack, "Comparing the ACS/WFC and WFC3/UVIS Calibration and Photometry" is now posted.

16 Feb 2018 ISR 18-01 by V. Kozhurina-Platais et al, "Accuracy of the HST Standard Astrometric Catalog w.r.t. Gaia" is now posted.

Software Updates

In January of this year, the ACS Team released a version of CALACS, version 10.0.0, that will be installed with the most recent version of HSTCAL, v2.0.0, as part of the HSTDP 2018.1 pipeline release. This version contains all the updates made to CALACS v9.2.0, in addition to the several improvements made in v10.0.0. This release is the largest since CALACS in HSTDP 2012.2 containing many updates and improvements to the calibration routines used in CALACS.

Out-dated Webpages

In light of these updates, the ACS Team is currently working to update all webpages referencing previous versions of CALACS. This is a work in progress and so whenever possible, we strongly recommend that users refer to the documentation in the most recent version of the ACS Data Handbook (v9.0) published in February 2018. If you are still unable to find an answer to your question, please submit a help ticket at We apologize for any inconvenience this may cause and thank you for bearing with us.

-The ACS Team

A brief summary of the major updates to CALACS in v9.2.0 and v10.0.0 are as follows:

Updates in v9.2.0

  • The implementation of sink pixel corrections (SINKCORR) resulting in updated Data Quality arrays (See ISR 17-02)
  • The implementation of an updated pixel based CTE correction (See ISR 18-04)
  • The addition of the Data Quality bit flag, 32, which characterizes pixels to be unstable throughout the course of an anneal period (See ISR 17-05)
  • An enhanced bias level correction that now correctly calculates the bias level for amplifiers B and D in subarrays
  • MAST Newsletter for September 2017: The New CALACS

Updates in v10.0.0

  • A bug that resulted in incorrect error propagation for CRSPLIT observations combined with ACSREJ has been fixed
  • The ACSREJ algorithm has been updated to use the ERR arrays when rejecting cosmic rays
  • Amp-dependent read noise thresholds were implemented in the CTE correction
  • A bug affecting CRSPIT data with PCTECORR=PERFORM that caused the non-cte corrected superdark to be used in dark subtraction has been fixed.

Release notes for all HSTCAL versions are posted in the github repository.

Current ACS Status

SBC is operating nominally.

HRC is not operational.

WFC is operating nominally.