Delivery, installation, on-sky verification of the Hobby Eberly Telescope wide field corrector

Abstract

The Hobby-Eberly Telescope (HET) † , located in West Texas at the McDonald Observatory, operates with a fixed segmented primary (M1) and has a tracker, which moves the prime-focus corrector and instrument package to track the sidereal and non-sidereal motions of objects. We have completed a major multi-year upgrade of the HET that has substantially increased the pupil size to 10 meters and the field of view to 22 arcminutes by deploying the new Wide Field Corrector (WFC), new tracker system, and new Prime Focus Instrument Package (PFIP). The focus of this paper is on the delivery, installation, and on-sky verification of the WFC. We summarize the technical challenges encountered and resolutions to overcome such challenges during the construction of the system. We then detail the transportation from Tucson to the HET, on-site ground verification test results, post-installation static alignment among the WFC, PFIP, and M1, and on-sky verification of alignment and image quality via deploying multiple wavefront sensors across 22 arcminutes field of view. The new wide field HET will feed the revolutionary new integral field spectrograph called VIRUS, in support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), a new low resolution spectrograph (LRS2), an upgraded high resolution spectrograph (HRS2), and later the Habitable Zone Planet Finder (HPF).

Arrayed wide-field astronomical camera system for spectroscopic surveys on Extremely Large Telescopes: system architecture, proof-of-concept, and enabling technologies

“…Looking back, we recognize that astronomical correctors traditionally consist of 3 to 8 large monolithic meniscus lenses 13,14 plus a set of ADC prisms (except the cases of the HET 15 and the South African Large Telescope 16 where field correctors are comprised of mirrors), all following completely one-off construction process. Although this approach did work, scaling it to larger and larger aperture telescopes inevitably resulted in field correctors with greater volume, complexity, and cost.…”

The HETDEX Instrumentation: Hobby-Eberly Telescope Wide Field Upgrade and VIRUS

“…The requirement to survey large areas of sky with VIRUS plus the need to acquire wavefront sensing stars to provide full feedback on the tracker position led us to design an ambitious new corrector employing meter-scale aspheric mirrors and covering a 22-arcmin diameter field of view. The WFU (Hill et al 2018b;Lee et al 2022) deploys the wide field corrector (WFC, Burge et al 2010;Oh et al 2014;Good et al 2014a;Lee et al 2016), a new tracker (Good et al 2018), a new prime focus instrument package (PFIP, Vattiat et al 2014), new software control systems (Beno et al 2012;Ramsey et al 2016Ramsey et al , 2018, and new metrology systems (Lee et al 2018a,c). The metrology systems provide closed-loop feedback on all axes of motion and the optical configuration of the telescope.…”

“…The WFC has uniform plate scale over the entire field of view to ensure that the dither offsets to fill in the gaps between fibers in VIRUS IFUs are close to identical for all IFUs (variation is 0.4%). The WFC was manufactured by the University of Arizona College of Optical Sciences (Burge et al 2010), with significant collaboration from MDO (Lee et al 2016, Good et al 2014a). The smaller M4 was subcontracted to Precision Asphere.…”

“…Details of the figuring, alignment, and testing at the College of Optical Sciences are given in Burge et al (2010), Oh et al (2014), and Lee et al (2016). During initial testing, significant errors in the low-order figures of M5 and M3 were detected.…”

“…During initial testing, significant errors in the low-order figures of M5 and M3 were detected. Respacing the mirrors and adding an aspheric corrector plate at the exit pupil in place of the planar exit window brought the performance of the WFC back to the image quality specification (Lee et al 2016). Final alignment utilized interferometric testing against computer generated hologram targets.…”