Issue affecting some proposals requiring ACA observations

An issue has been discovered in the Cycle 10 ALMA Observing Tool (OT) that affects the estimated Atacama Compact Array (ACA) integration times for some ACA observations (7-m and TP). The issue occurs when the Bandwidth used for Sensitivity in the "Control and Performance" section is set to anything other than RepWindowEffectiveChannelWidth or FinestEffectiveChannelWidth and a 4x4-bit spectral mode is selected. This is a result of an error in the implementation of the 4x4-bit spectral mode for improved sensitivity (that is offered in Cycle 10 on the 12-m Array only), which causes the integration times for ACA observations calculated by the OT to be erroneously too short when a 4x4-bit spectral mode is selected, unless the above bandwidth for sensitivity options are selected. In addition, the OT erroneously allowed 4x4-bit spectral modes to be selected with ACA standalone mode. We have fixed these problems and a patched version of the Cycle 10 OT is now available on the Science Portal. All PIs of projects that include ACA observations should download the updated OT version and submit or resubmit their proposals using this version. The correct version can be identified by checking for the words “Patch 1” in the title bar at the top of the OT window.

Additional issue affecting the Cycle 10 (Phase 1 Patch 1) OT

In the Cycle 10 (Phase 1 Patch 1) OT, if ‘Standalone ACA’ is selected in the ‘Control and Performance’ panel, integration times are underestimated if the Bandwidth used for Sensitivity (BufS) is set to ‘RepWindowEffectiveChannelWidth’ or to ‘FinestEffectiveChannelWidth’. PIs should set the BufS to ‘User’ to prevent this miscalculation. Please note that the ‘User’ choice allows you to set a value that is equivalent to either the ‘RepWindowEffectiveChannelWidth’ or the ‘FinestEffectiveChannelWidth’, but in these cases the time estimate will be correct. Single continuum observations or observations requiring the 12-m array are not affected by this problem.

We regret any inconvenience or impact experienced by our ALMA users due to these issues. If you have any questions, or have comments or concerns, please contact your local ALMA Regional Centre via the ALMA Helpdesk at https://help.almascience.org/.