Integration of VIRUS spectrographs for the Hobby-Eberly Telescope Dark Energy Experiment

Abstract

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX ‡ ) at the University of Texas McDonald Observatory will deploy the Visible Integral-Field Replicable Unit Spectrograph (VIRUS) to survey large areas of sky. VIRUS consists of up to 192 spectrographs deployed as 96 units. VIRUS units are fiber-fed and are housed in four enclosures making up the VIRUS Support Structure (VSS). Initial design studies established an optimal array size and an upper and lower bound on their placement relative to the existing telescope structure. Tradeoffs considering IFU (optical fiber) length, support structure mass and ease of maintenance have resulted in placement of four 3 x 8 arrays of spectrograph pairs, about mid-point in elevation relative to the fixed HET structure. Because of the desire to minimize impact on the modal performance of the HET, the VSS is required to be an independent, selfsupporting structure and will only be coupled at the base of the telescope. Analysis shows that it is possible to utilize the existing azimuth drives of the telescope, through this coupling, which will greatly simplify the design and reduce cost. Each array is contained in an insulated enclosure that will control thermal load by means of heat exchangers and use of facility coolant supply. Access for installation and maintenance on the top, front, and rear of the enclosures must be provided. The design and analysis presented in this paper must provide an optimum balance in meeting the stringent requirements for science and facility constraints such as cost, weight, access, and safety.

VIRUS: a massively replicated 33k fiber integral field spectrograph for the upgraded Hobby-Eberly Telescope

“…Initially, locations around the top hexagon of the HET structure were explored, resulting in a minimum fiber length of 15 m. Models linking instrument performance to sensitivity and predicted number of LAEs detected in the HETDEX survey allowed a trade-off between fiber length, cost, and survey requirements. Analysis of the structure required to support the VIRUS instruments (total weight 30,000 kg) indicated that there is significant expense associated with the high location, and we have undertaken a trade-off between performance and location of VIRUS, with the result that we have chosen a lower location for the VIRUS enclosures with a 20 m average length of IFU fiber 15,51 .…”

Design and construction progress of LRS2-B: a new low resolution integral-field spectrograph for the Hobby-Eberly Telescope

“…Since LRS2-B is based on VIRUS, its operation will be congruent with the VIRUS spectrograph array. LRS2-B will be rack mounted in the VIRUS support structure 45 and will connect to the large liquid nitrogen cryogenic plumbing manifold that provides coolant for the VIRUS spectrograph array. 32 While the two LRS2-B CCDs share a common data system architecture with VIRUS, they will be read out through a dedicated computer for data acquisition rather than through the multiplexed VIRUS detector system since the instruments are operated independently.…”

Performance verification testing for HET wide-field upgrade tracker in the laboratory

“…degrees, the HET design, coupled with a small field of view corrector, hampers programs where objects have higher sky densities. In seeking a strong niche for the HET going forward, the HET field of view will be increased from 4′ to 22′ so that it can accommodate the Visible Integral-field Replicable Unit Spectrograph (VIRUS) [1][2][3][4][5] , an innovative, highly multiplexed spectrograph that will open up the emission-line universe to systematic surveys for the first time, uncovering populations of objects selected by their line emission rather than by their continuum emission properties.…”