A new software tool to predict astrometric errors for ELTs

Extremely Large Telescopes (ELTs) have precision requirements of a few tens of micro-arcsec for differential astrometry science cases. Each ELT project has its own astrometric error budget taking into consideration the specific design parameters of the observatory. A version of the Thirty Meter Telescope (TMT) astrometry error budget has previously been established and the details were presented at SPIE 2016.1 In this paper, we briefly revisit this error budget analysis. The main focus of this paper is a new python-based astrometry calculator which was developed for a more user-friendly application of the error budget. It facilitates direct evaluation of and comparison between different scenarios such as absolute vs differential astrometry; dense vs spare observation fields; science fields with and without reference objects, etc. The details of the astrometry calculator and its general functions are described. A few example science sensitivity studies are presented and the procedure of estimating astrometric errors for other observatories is outlined.