wide field optical spectrograph - wfos architecture

Context:WFOSisafirstlightinstrument.The2016/2017OMDRphaseconcludedthatthepreviousconcepthadinsurmountabletechnicalchallenges.DuringtheOMDRandWFOSConceptualDesign1phases,fiberandreconfigurable(Xchange)spectrographarchitecturesweredeveloped(2017/2018).Top:IllustrationsofthesamplingoftheTMTfocalplanefortheXchange(farleft)andfiberfedformsoftheWFOSinstrumentwhenskynodding.7’diameterfieldisfor4modularspectrographswith22”pitch,100%overlapfiberpositioners.Left:Xchange-WFOSinstrumentdesignconcept(upper)andopticallayout(lower)showingarticulatedcamerapositionsforhighspectralresolutionmodes.Right:ModularFiber-WFOSinstrumentdesignconceptshowingthefullpotential9spectrographsand700fibercollectorsover10’field(baselineis4spectrographs).BackgroundsubtractionwithFibersAnalysisshowsthatforobservationslastingmanyhours,requiringskysubtractionprecisionof0.1%,negligiblefibersystematicsareexpectedwhensky-nodding.

https://www.ucolick.org/home/facilities/instruments/wfos.html

Principalinvestigator:KevinBundy Projectmanager:MaureenSavage(UCObservatories)Projectscientist:ChuckSteidel(Caltech) Crosspartnershipdevelopmentteam

Downselectionprocessandtimeline:-Technicalreview4/5April,2018–Concludedallarchitecturesaretechnicallyfeasible-Re-assessmentoftoplevelWFOSsciencerequirementsbySAC,usingcommunityinput–26July,2018-Downselecttosinglearchitecture–EarlyOctober2018

8.3’

3’

1”

60targets 155sky-targetpairs–4spectrographs

KeyScienceareasdrivingthedesigns:

-  IGM/CGMtomographyandcharacterization-  Stellarpopulationsthroughoutthelocalgroup-  Highredshiftgalaxyevolution-  Transientscience

Xchange-WFOS Fiber-WFOS

Spectralresolution Baseline1500–5000,gratingdependent Fixed3500to5000.Binningforlowerresolution

Limitingmagnitude ~24.1g(AB)in1hrS/N=5 ~24.0g(AB)(Compareto22.1forGMOS)

Wavelengthcoverage

0.31-1.0μmcontinuousatR=1500.40nmintheblue,140nmintheredatR=4500

0.31-1.0μmcontinuousatR=5000

Xchange-WFOS Fiber-WFOS-baseline4spectrographs

Focalplanefor9spectrographs

WideFieldOpticalSpectrograph-WFOSArchitectureDownselect

Slitbasedmonolithic-versus-fiber-fedmodular