ACS STAN January 2025

January 10, 2025

ACS NEWSLETTERS

Table of Contents

1. Serial CTE correction implemented in CALACS 10.4.0

J. Ryon, N. Grogin

Pixel-based serial (X-direction) CTE correction has been implemented in the latest version of CALACS, 10.4.0, as part of hstcal version 3.1.0. This version of CALACS requires the latest PCTETAB reference file, 8ch1518tj_cte.fits. This latest PCTETAB reference file contains 16 additional extensions (four per amplifier) compared to the previous version and is incompatible with older versions of CALACS. Older versions of the PCTETAB will not work with CALACS v10.4.0 or later.

In the standard calibration pipeline, the new serial CTE correction and the parallel (Y-direction) corrections are both run by default on all full-frame WFC exposures obtained after SM4 (May 2009). The parallel correction alone is run on pre-SM4 data since serial CTE losses are very minor during that time. The serial CTE correction is not currently available for subarray data, but the parallel CTE correction remains available for supported subarray modes through the use of acstools.acs_destripe_plus.

More details can be found in ACS ISR 2024-07.

2. Documentation for HST Cycle 33 released

The ACS Team

Documentation relevant to the preparation of HST Cycle 33 ACS proposals has been released. This includes:

- ACS Instrument Handbook

- HST Call for Proposals

- HST Primer

ACS/WFC is offered as a shared risk in Cycle 33 and may receive minimal calibration and support. WFC support in future cycles is contingent on the outcome of the 2025 Senior Review. Observers interested in using ACS/WFC are encouraged to explore whether their scientific goals can be accomplished with other HST modes. More details are provided in the documentation linked above.

3. New "Fleck" on WFC detector and updated bad pixel table (BPIXTAB)

N. Hathi, S. Hoffmann, J. Ryon, and the ACS Team

Here, we report the discovery of a new small artifact on ACS/WFC imagery, the first one since 2017. It appeared on the ACS/WFC detector as of July 9, 2024, centered at pixel coordinates (3719, 1875) on the WFC Chip 1. The ACS team at STScI discovered three similar image artifacts in 2017, called 'flecks' due to their shape. These artifacts were added to the existing list of similar artifacts from previous years. A detailed investigation of the 2017 flecks was discussed in the ACS ISR 2018-03, focusing on their properties and possible causes. It was found that all these flecks, from 2017 and earlier, have remained stable over the lifetime of the ACS/WFC. Since the discovery of flecks in 2017, the ACS team has been monitoring the ACS/WFC calibration images for any new flecks that appear on the detector, leading to the discovery of this new small fleck.

Pixels associated with the new fleck that have less than 50% transmissivity (a total of 13 pixels) have been added to the ACS/WFC bad-pixel table (BPIXTAB file '8c619592j_bpx.fits') with data-quality flag=4, effective July 9, 2024. The CALACS pipeline will accordingly flag the WFC image data quality (DQ) array at these pixel locations, preventing their use in DQ-aware applications such as DrizzlePac.

4. ACS posters at the January 2025 AAS meeting

“The impact of imperfect charge transfer efficiency on point- and extended-sources in ACS/WFC imaging” by D. Stark, N. Grogin, and M. Chiaberge.
"Celestial Matchmaking: Cross-Matching HST/ACS Data with GAIA DR3" by M. Booth and Y. Cohen.

5. Recent Instrument Science Reports

For a complete list with abstracts, please visit the ACS ISR webpage.

ACS ISR 2024-07 “Serial Charge Transfer Efficiency in ACS/WFC” (Ryon and Grogin)