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

摘要

The upcoming Wide-Field Upgrade (WFU) has ushered in a new era ofinstrumentation for the Hobby-Eberly Telescope (HET). Here, we present thedesign, construction progress, and lab tests completed to date of theblue-optimized second generation Low Resolution Spectrograph (LRS2-B). LRS2-Bis a dual-channel, fiber fed instrument that is based on the design of theVisible Integral Field Replicable Unit Spectrograph (VIRUS), which is the newflagship instrument for carrying out the HET Dark Energy eXperiment (HETDEX).LRS2-B utilizes a microlens-coupled integral field unit (IFU) that covers a7"x12" area on the sky having unity fill-factor with ~300 spatial elements thatsubsample the median HET image quality. The fiber feed assembly includes anoptimized dichroic beam splitter that allows LRS2-B to simultaneously observe370 nm to 470 nm and 460 nm to 700 nm at fixed resolving powers of R \approx1900 and 1200, respectively. We discuss the departures from the nominal VIRUSdesign, which includes the IFU, fiber feed, camera correcting optics, andvolume phase holographic grisms. Additionally, the motivation for the selectionof the wavelength coverage and spectral resolution of the two channels isbriefly discussed. One such motivation is the follow-up study of spectrally and(or) spatially resolved Lyman-alpha emission from z ~ 2.5 star-forming galaxiesin the HETDEX survey. LRS2-B is planned to be a commissioning instrument forthe HET WFU and should be on-sky during quarter 4 of 2013. Finally, we mentionthe current state of LRS2-R, the red optimized sister instrument of LRS2-B.