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15th of October 2020
Precise radio astrometry and new developments for the next-generation instruments
by Maria Rioja and Richard Dodson
Maria J. Rioja (CASS/ICRAR-UWA, OAN) and Richard Dodson (ICRAR-UWA) have published an Astronomy & Astrophysics Review paper that focuses on the achievements to date and the future of high-precision astrometry, enabled by the exciting new opportunities with next-generation radio instruments. It encompasses applications across the full radio frequency spectrum, using both ground and space-based VLBI observations.

In this work, current and next-generation astrometric analysis techniques are synthesised into a common framework, governed by a simple relationship. This provides clear guidance on the key technological requirements to enable ultra-precise astrometric measurements, potentially reaching 1-microarcsecond with the SKA-VLBI and other next-generation instruments, and therefore opening up new innovative high-impact science possibilities.

The figure above, from the paper, shows a schematic of a VLBI interferometric array, comprising diverse elements on the ground and in space. The propagation of the cosmic signal through the turbulent tropospheric and ionospheric components of the atmosphere introduces contaminating delays, as does the instrumentation, which need to be removed in the analysis; this is the essence of astrometric calibration.

The figure shows a variety in the nature and size of the elements in a VLBI-array in the era of the next-generation of instruments. Alongside the moderate-sized single-dish telescope on the right, there are the large collecting areas provided by a massive single dish or many smaller dishes from a connected array phased-up, and also the extremely long baselines provided by a radio telescope in space. New technologies are fundamental to remove the systematic errors that limit current astrometric observations. Multi-pixel capabilities (illustrated with narrow orange cones) and simultaneous multi-frequency coverage (illustrated with the two-tone incoming wavefront), can provide matching Fields of View (light orange cones) from all of these elements and the capability for multi-frequency observations, respectively. These next-generation technologies, combined with the next-generation analysis techniques, will deliver an order of magnitude improvement in astrometric precision and frequency coverage with the next-generation instruments. (Image Credit: Maria J. Rioja (CASS/ICRAR-UWA, OAN) and Richard Dodson (ICRAR-UWA))

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