Issue affecting ALMA polarization and VLBI data taken in Cycle 8

Published: 08 Jul 2022
Milky Way and star trails over ALMA

An issue has been identified in ALMA data taken since the start of Cycle 8 (1 October 2021). The orientation angle of the linearly polarized receiver elements is recorded incorrectly in the raw data (ASDMs). Full polarization and VLBI data are critically impacted. These data are currently being reprocessed and, when necessary, re-delivered under the observatory's QA3 policy. Any data taken in Cycle 8 other than polarization or VLBI data are not impacted, but they will still have their ASDMs updated in the archive for consistency purposes, but without reprocessing. For the remainder of Cycle 8, all data will be fixed before processing and ingestion. The issue has already been corrected in the Cycle 9 data acquisition software.

We regret any inconvenience or impact experienced by our ALMA users due to this issue. If you have any questions, or have comments or concerns, please contact your local ALMA Regional Center via the ALMA Helpdesk at