2025AJ....169...36L

MagAO-X is a recently commissioned extreme adaptive optics instrument for the Magellan Clay 6.5 m telescope at Las Campanas Observatory in Chile. MagAO-X had first light in 2019 and subsequent commissioning observations in 2022 and 2023. An essential step for the commissioning of any new instrument is the calibration of the conversion of detector coordinates to angular sky coordinates, which we accomplish with observations of HD 165054. The background stars adjacent to HD 165054 in Baade's Window are in a fortuitous configuration for the astrometric calibration of natural-guide-star high-contrast imaging instruments. We extend past work to connect these stars' positions to absolute astrometry for HD 165054 itself using Gaia Data Release 3 data, and bootstrap the creation of an astrometric solution for our new high-contrast imaging instrument. Through Markov Chain Monte Carlo analysis of the historical data and position measurements from MagAO-X, we obtain updated astrometric parameters for the seven background stars and an astrometric calibration of the MagAO-X science cameras.