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

Abstract

The Hobby–Eberly Telescope (HET) Dark Energy Experiment (HETDEX) is undertaking a blind wide-field low-resolution spectroscopic survey of 540 deg2 of sky to identify and derive redshifts for a million Lyα-emitting galaxies in the redshift range 1.9 < z < 3.5. The ultimate goal is to measure the expansion rate of the universe at this epoch, to sharply constrain cosmological parameters and thus the nature of dark energy. A major multiyear Wide-Field Upgrade (WFU) of the HET was completed in 2016 that substantially increased the field of view to 22′ diameter and the pupil to 10 m, by replacing the optical corrector, tracker, and Prime Focus Instrument Package and by developing a new telescope control system. The new, wide-field HET now feeds the Visible Integral-field Replicable Unit Spectrograph (VIRUS), a new low-resolution integral-field spectrograph (LRS2), and the Habitable Zone Planet Finder, a precision near-infrared radial velocity spectrograph. VIRUS consists of 156 identical spectrographs fed by almost 35,000 fibers in 78 integral-field units arrayed at the focus of the upgraded HET. VIRUS operates in a bandpass of 3500−5500 Å with resolving power R ≃ 800. VIRUS is the first example of large-scale replication applied to instrumentation in optical astronomy to achieve spectroscopic surveys of very large areas of sky. This paper presents technical details of the HET WFU and VIRUS, as flowed down from the HETDEX science requirements, along with experience from commissioning this major telescope upgrade and the innovative instrumentation suite for HETDEX.

Seven Years of SN 2014C: A Multiwavelength Synthesis of an Extraordinary Supernova

“…The spectra and IFU images of SN 2014C reported here were obtained with LRS2 (Chonis et al 2016) on the 10 m Hobby-Eberly Telescope (HET; Ramsey et al 1998;Hill et al 2021). LRS2 comprises two IFU spectrographs separated by 100″ on sky: LRS2-B (3650-6950 Å) and LRS2-R (6450-10500 Å).…”

Surface Brightness Profile of Lyman-α Halos out to 320 kpc in HETDEX

“…We use spectra from the internal data release 2.1.3 (DR 2.1.3) of HETDEX, which were obtained with the Visible Integral-field Replicable Unit Spectrograph (VIRUS) on the 10 m Hobby-Eberly Telescope (HET; Ramsey et al 1994;Hill et al 2021). VIRUS consists of up to 78 integral-field unit fiber arrays (IFUs), each of which contains 448 1 5 diameter fibers and spans 51″ × 51″ on the sky.…”

“…The gaps between the IFUs remain, so that the filling factor of one observation is ∼1/4.6. Details of the upgraded HET and the VIRUS instrument can be found in Hill et al (2021).…”

“…Multiple independent techniques show that the PSF of VIRUS is well modeled by a Moffat function with β ä [3, 3.5] in good seeing conditions (Gebhardt et al 2021;Hill et al 2021). To test this, we measure the median radial profile of Gaia stars observed by VIRUS in the same observations as the LAEs.…”

“…Because the dominant origin of the Lyα halo photons depends on, among other things, the distance to the galaxies (Byrohl et al 2021;Mitchell et al 2021), observations of Lyα profiles out to larger distances will be helpful. An ideal data set for this is provided by the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX; Hill et al 2008;Gebhardt et al 2021;Hill et al 2021), which is designed to detect more than one million LAEs at redshifts 1.9 < z < 3.5 in a 10.9 Gpc 3 volume to measure their clustering and thereby constrain cosmological parameters. HETDEX detects emission lines by simultaneously acquiring tens of thousands of spectra without any preselection of targets.…”