Post-wide-field-upgrade imaging performance evaluation of the Hobby-Eberly Telescope

The Hobby-Eberly Telescope (HET) is an innovative 10m-class telescope that operates with a fixed-altitude segmented spherical primary mirror (M1) while a tracker, located at the top of the telescope, moves the prime-focus spherical aberration corrector (SAC) and instrument package in order to track the sidereal and non-sidereal motions of celestial objects. In 2016, we completed the wide-field upgrade of the telescope, which includes the Wide-Field Corrector (WFC), the tracker, the prime focus instrument package, and all electromechanical hardware and telescope control software. Post the upgrade, we have been monitoring the imaging performance of the telescope through the in-situ metrology systems. These systems highlight weak spots of the telescope facility in imaging performance and provide quantitative guidance to specific facility repair and/or upgrades to further improve the HET's overall performance. This paper discusses our long-range (7yrs) datasets, specific analysis techniques used, and current outcomes of this investigative effort in the context of specific facility improvement and upgrade plans.