ALMA North America Cycle 3 Study Project Final Report: Extensions and Enhancements to the ALMA Phasing System

Abstract

The Atacama Millimeter/submillimeter Array (ALMA) Phasing Project (APP) has successfully brought Very Long Baseline Interferometry (VLBI) to ALMA. Nine VLBI science projects were observed in 2017 during ALMA’s in augural VLBI campaign as part of Cycle 4. This marked the culmination of an international 5-year effort that involved both hardware and software contribu- tions from the APP Team to the ALMA Observatory. A Cycle 3 ALMA North America (NA) Study was proposed to enable ongoing support of VLBI at ALMA and the investigation of enhancements to the ALMA Phasing System (APS) that were not within the scope of the original APP project. These included: (1) an extension of phasing capabilities to the submilleter (Band 7); (2) an exploration of correlation techniques to compensate for the mismatch in sampling rates between ALMA and other VLBI stations; (3) prescriptions for optimization of ALMA baseband delay application; (4) defining and documenting data calibration and analysis pathways for experiments utilizing phased ALMA data. This report summarizes outcomes from the Cycle 3 Study. Work on the APP remains ongoing under a Cycle 4 Study award and will continue under a pending ALMA NA Cycle 5 Development Project that is expected to enable full implementation of the capabilities explored under the Cycle 3 and Cycle 4 Studies.