MSE Science Requirements Document · REQ-SRD-025 Spatially resolved spectra Requirements relating...

MSEScienceRequirementsDocument

MSE.PO.SCI.DOC-REQ-001Version:C

Status:Released

2017-05-08PreparedBy: Name(s)andSignature(s) Organization DateAlanMcConnachie

MSEProjectScientist

2015Oct21

ApprovedBy: NameandSignature Organization DateRickMurowinski

MSEProjectManager

2015Oct23

MaunakeaSpectroscopicExplorer

Title: Science Requirements Document Doc # : MSE.PO.SCI.DOC-REQ-001

Date: 2017-05-08 Status: Version C Page: 2 of 25

ChangeRecord

Version Date Affected

Section(s)Reason/Initiation/Remarks

A 2015-10-23 All FirstRelease

B 2015-11-04 AllFormatrequirementsforDOORSimport(KeiSzeto/LaurieDale)

C 2017-05-08 All

Updateddocumentnumber;Minortextedits;UpdatedTable1;InsertedTable3;AddedAbbreviationsandAcronymsasSection3Improvedjustificationandnotesformultiplerequirements,includingcross-referencingrequirementstoDSCREQ-SRD-013:changedtoreflectnewhighresolutioncapabilities;REQ-SRD-021:changedtoScienceFieldofViewinsteadofEtendue;REQ-SRD-033:modifiedtoreflectnewhighresolutioncapabilities,includingmovingredcutoffto900nmfrom950nm;REQ-SRD-034/35/36:betterdefinedIQcondition(definedinrbandfor034/35andingbandfor036)REQ-SRD-42:correctedto10km/sprecisionfrom9km/s(previously,atypo);REQ-SRD-046:valueadded(changedfromNN.n)REQ-SRD-051,/052:updated---(AlanMcConnachie)



1 PURPOSE.......................................................................................................................42 RELATEDDOCUMENTSANDDRAWINGS......................................................................52.1 ReferenceDocuments............................................................................................52.2 ApplicableDocuments...........................................................................................5

3 ABBREVIATIONSANDACRONYMS................................................................................54 SCIENCEREQUIREMENTS.............................................................................................64.1 SummaryofMSEScienceCapabilities....................................................................64.2 IndividualRequirements......................................................................................104.2.1 REQ-SRD-011Lowspectralresolution...........................................................104.2.2 REQ-SRD-012Moderatespectralresolution..................................................104.2.3 REQ-SRD-013Highspectralresolution..........................................................114.2.4 REQ-SRD-021Sciencefieldofview................................................................124.2.5 REQ-SRD-022Multiplexingatlowresolution................................................124.2.6 REQ-SRD-023Multiplexingatmoderateresolution......................................134.2.7 REQ-SRD-024Multiplexingathighresolution...............................................144.2.8 REQ-SRD-025Spatiallyresolvedspectra........................................................154.2.9 REQ-SRD-031Spectralcoverageatlowresolution........................................154.2.10 REQ-SRD-032Spectralcoverageatmoderateresolution............................164.2.11 REQ-SRD-033Spectralcoverageathighresolution.....................................164.2.12 REQ-SRD-034Sensitivityatlowresolution..................................................174.2.13 REQ-SRD-035Sensitivityatmoderateresolution........................................184.2.14 REQ-SRD-036Sensitivityathighresolution.................................................194.2.15 REQ-SRD-041Velocitiesatlowresolution...................................................194.2.16 REQ-SRD-042Velocitiesatmoderateresolution.........................................204.2.17 REQ-SRD-043Velocitiesathighresolution..................................................214.2.18 REQ-SRD-044Relativespectrophotometry..................................................214.2.19 REQ-SRD-045Skysubtraction,continuum...................................................224.2.20 REQ-SRD-046Skysubtraction,emissionlines..............................................234.2.21 REQ-SRD-051Accessiblesky........................................................................234.2.22 REQ-SRD-052Scienceobservingefficiency..................................................244.2.23 REQ-SRD-053Observatorylifetime..............................................................244.2.24 REQ-SRD-061++Dataprocessingandmanagement....................................25



1 Purpose

ThisistheMSEScienceRequirementsDocument(SRD).ItrepresentsthehighestlevelofrequirementsthattheMSEfacilitymustmeet,andeveryrequirementdescribedhereinistraceddirectlytoakeysciencedriverforthefacility.ThekeysciencedriversaredescribedintheDetailedScienceCase(DSC)fortheMaunakeaSpectroscopicExplorer:TheCompositionandDynamicsoftheFaintUniverse[RD-01],whichprovidesanarrativedescribingthescientificimportanceofMSEtoaddressfundamentalquestionsregardingthenatureofstars,galaxiesandtheUniverse.ItisfullyexpectedthatthescientificscopeandimpactofMSEthatiscurrentlyenvisionedanddescribedintheDSCisincomplete;thekeysciencequestionsnaturallyandcontinuallyevolveorchangedramaticallyasourunderstandingadvancesandnewdiscoveriesaremade.ToensurethatthedesignofMSEwillbebestoptimizedtoaddressabroadrangeoftransformationalscienceduringitslifetime,theDSCadditionallydescribesasuiteof“ScienceReferenceObservations”(SROs)thattogetherconstitutetheequivalentofa“DesignReferenceMission”forthefacility.TheSROshavebeenidentifiedbytheinternationalscienceteamasspecificsciencegoalsthatarehighimpact,transformational–i.e.,willprovideahighlyimportantandsignificantincreaseinourunderstandingofthefield–andwhichareuniquelypossiblewithMSE.Theyhavebeendevelopedinconsiderabledetail,withparticularfocusonimplementationissuessuchastheoriginofpre-imaging,theluminositydistributionoftargets,theirspacedensityandthesurveyregionrequired,thespecificspectralfeaturesthatmustbeobserved,thequalityofthemeasurementthatisrequired,theobservingcadence,anyspecialcalibrationmeasurements,andrelatedissues.SciencerequirementsarethendefinedasthecapabilitiesthattheMSEsystemmusthaveinordertomakethemeasurementsnecessarytosuccessfullycarryouttheprogramsdescribedbytheSROs.AtsciencecommissioningforMSE,andduringitsfirstdecadeofoperations,manyoftheobservingprogramsthatMSEwillundertakemayaddressdirectlythesciencedescribedbytheSROs.Quitepossibly,amorecontemporarysetofobservationswillbeconducted.Nevertheless,itisexpectedthatthecapabilitiesthatarecapturedbythesciencerequirementswillensurethatMSEbecomesthepremierinternationalfacilityformultiplexedspectroscopy,enablingavastrangeofhigh-impactscienceprograms.MSEisenvisionedasagroundbased,dedicated,widefield,highlymultiplexedspectroscopicfacility.Allsciencecases,SROsandfacilitysynergiesdescribedintheDSCassumethisbasicarchitecture.Withinthiscontext,thesciencerequirementslistedinthispresentdocumentdescribe,wheneverpossible,system-levelperformanceatthe



end-userlevel.Thispointisimportantandworthexpounding.Atthelevelofthesciencerequirements,distinctionsbetweenmajorsub-systemssuchasthetelescope,fiber-system,andspectrographs,aregenerallyunnecessaryandmayimpedethedesignoftheoptimalsystem.Wethereforetrytomakeexplicitthedistinctionbetweenasciencerequirement,andadesignsolutionthatmeetsthesciencerequirement.Agoodexampleis“sensitivity”.Atthelevelofthesciencerequirements,whatisimportantistheobservedsignaltonoiseratioperresolutionelementforagivenspectralresolutionasafunctionofwavelength.Thismightbeachievedwitharelativelysmallapertureandhighthroughputoptics,oritmightbeachievedwithadesignthathasalargeraperturetoallowformoreleewayinotheraspectsoftheopticaldesign.Botharesatisfactorysolutions.Whereverpossible,carehasbeentakentoensurethesciencerequirementsaregenerallydescribedinawaythatdoesnotexplicitlyassumeadesignsolution.

2 RelatedDocumentsandDrawings2.1 ReferenceDocuments

Reference Documenttitle Date DocumentID[RD-01]

[RD-02][RD-03]

TheDetailedScienceCasefortheMaunakeaSpectroscopicExplorer:theCompositionandDynamicsoftheFaintUniverseMSEOperationsConceptDocumentMSEObservatory:TechnicalNote–SkySubtractionAccuracy

2017-02-082016-12-162016-02-11

MSE.PO.SCI.DOC-RPT-001MSE.PO.ENG.DOC-REQ-002MSETN005

2.2 ApplicableDocuments

Reference Documenttitle Date DocumentID

3 AbbreviationsandAcronyms

AGN ActiveGalacticNucleiCFHT Canada-France-HawaiiTelescopeDSC DetailedScienceCaseIFU IntegralFieldUnitIGM Inter-galacticmediumIQ ImageQualityLSST LargeSynopticSurveyTelescope



M31 Messier31(theAndromedaGalaxy)MSE MaunakeaSpectroscopicExplorerNIR Nearinfra-redrms rootmeansquareSKA SquareKilometerArraySNR SignaltoNoiseRatioSRD ScienceRequirementsDocumentSRO ScienceReferenceObservationTBC TobeconfirmedTBD Tobedetermined

4 ScienceRequirements

Thesciencerequirementsaresummarizedatvariouspointsthroughoutthisdocument.Incaseofanyinconsistenciesinthetext,therequirementsanddescriptionsgiveninSection4.2takeprecedence.

4.1 SummaryofMSEScienceCapabilities

Table1isacopyofTable2fromtheDSC,andprovidesasummaryofthemajor,highlevel,science-enablingcharacteristicsforMSEasdefineddirectlybythesciencerequirements.MSEwillconductmulti-objectspectroscopyforastrophysicalobjectslocatedanywhereinatleastthree-quartersoftheentiresky.ItwilloperateatthreedifferentspectralresolutionsspanningfromR ~2500to~40000,andwillobtainspectrastretchingfromblue-opticalwavelengthstothenear-infrared.Witha1.5squaredegreesciencefieldofview,MSEwillobtainatleast3200spectraperexposureatlowandmoderateresolutions,and~1000spectraperexposureathighresolution.Itwillconductsurveysthatincludemillionsoftargetsspreadoverpotentiallyseveraltensofthousandsofsquaredegrees.Duringitslifetimeitwillbeabletosupportamulti-objectIFUcapabilitytoallowforspatiallyresolvedstudiesofextendedsources.ThedatathatMSEwillproduceoverits>20yearlifetimewillbecalibratedtoahighlevelofaccuracyandrepeatability.Overall,thesescience-enablingcapabilitieswillprovidefortransformationalscientificdiscoveriesspanningaverybroadrangeofastronomicaltopics.



Table1:SummaryofthescientificcapabilitiesofMSE(updatedcopyofTable2fromtheDSC)

ThebasicarchitecturethatisassumedforMSEisasadedicated,ground-based,wide-fieldspectroscopicfacility,andwithinthiscontextallsciencerequirementsaretraceabletotheDSC.EachrequirementemergeseitherfromconsiderationofspecificormultipleSROsdescribedinthatdocument.ThesciencerequirementsaresummarizedinTable2,dividedintomajorsub-groupings.TheflowdownfromtheSROstothesciencerequirementsissummarizedbytheScienceTraceabilityMatrix,showninTable3(acopyofTable1fromtheDSC).Table2:SummaryofMSEsciencerequirements

RequirementsrelatingtoSpectralResolution:REQ-SRD-011 LowspectralresolutionREQ-SRD-012 ModeratespectralresolutionREQ-SRD-013 Highspectralresolution

RequirementsrelatingtotheFocalPlaneInput:REQ-SRD-021 SciencefieldofviewREQ-SRD-022 MultiplexingatlowresolutionREQ-SRD-023 MultiplexingatmoderateresolutionREQ-SRD-024 MultiplexingathighresolutionREQ-SRD-025 Spatiallyresolvedspectra

RequirementsrelatingtoSensitivityREQ-SRD-031 SpectralcoverageatlowresolutionREQ-SRD-032 SpectralcoverageatmoderateresolutionREQ-SRD-033 SpectralcoverageathighresolutionREQ-SRD-034 SensitivityatlowresolutionREQ-SRD-035 SensitivityatmoderateresolutionREQ-SRD-036 Sensitivityathighresolution

AccessibleskyAperture(M1inm)Fieldofview(squaredegrees)Etendue=FoVxπ(M1/2)2

Modes Moderate IFU

0.36-0.95μm J,Hbands 0.36-0.45μm 0.45-0.60μm 0.60-0.90μmSpectralresolution,R=λc/dλ 2500(3000) 3000(5000) 6000 40000 40000 20000Multiplexing >3200Spectralwindows ≈Half λc/30 λc/30 λc/15Sensitivity� m=23.5@SNR=2Velocityprecision� 9km/s@SNR=5Spectrophotometicaccuracy <3%relative♯Dichroicpositionsareapproximate

★Signal-to-noiseratiosaremeasuredperresolutionelement

IFUcapable;anticipatedsecond

generationcapability

30000squaredegrees(airmass<1.55)11.25m1.5149

>1000

m=20.0@SNR=10m=24@SNR=220km/s@SNR=5<3%relative

Full>3200

<100m/s@SNR=30N/A

Wavelengthrange 0.36-0.95μm0.36-0.90μm�0.36-1.8μm

Low High



RequirementsrelatingtoCalibrationREQ-SRD-041 VelocitiesatlowresolutionREQ-SRD-042 VelocitiesatmoderateresolutionREQ-SRD-043 VelocitiesathighresolutionREQ-SRD-044 RelativespectrophotometryREQ-SRD-045 Skysubtraction,continuumREQ-SRD-046 Skysubtraction,emissionlines

RequirementsrelatingtoLifetimeOperationsREQ-SRD-051 AccessibleskyREQ-SRD-052 ObservingefficiencyREQ-SRD-053 Observatorylifetime

RequirementsrelatingtoDataManagementandProcessingREQ-SRD-061++



Table3:ScienceReferenceObservationscross-referencedtoScienceRequirements.BoxeswithredbordersindicatethattheSROisusedinthederivationoftherequirement;darkgreenboxesindicatetherequirementishighlyrelevanttotheSRO;lightgreenindicatesthattherequirementhassomerelevancetotheSRO;greyindicatesminimalornoimpactoftheSROontherequirement.UpdatedcopyofTable1fromtheDSC.

DSC-SRO-01

DSC-SRO-02

DSC-SRO-03

DSC-SRO-04

DSC-SRO-05

DSC-SRO-06

DSC-SRO-07

DSC-SRO-08

DSC-SRO-09

DSC-SRO-10

DSC-SRO-11

DSC-SRO-12

Exoplanethosts

Timedom

ainstellarastrophysics

Chemicaltagging

intheouterGalaxy

CDMsubhalosand

stellarstreams

LocalGroup

galaxies

Nearbygalaxies

VirgoandCom

a

Halooccupation

GalaxiesandA

GN

TheInterGalactic

Medium

Reverberation

mapping

Peculiarvelocities

REQ-SRD-011 Lowspectralresolution

R~2000(whitedwarfs)

R~3000 R~3000 R~2000-3000 R~3000 R~3000 R~1000-

2000

REQ-SRD-012

Intermediatespectralresolution

Anyrepeatobservatio-ns

Essential,R~6500

Essential,R~6500

Essential,R~6500

Velocitiesoflowmassgalaxies

Velocitiesoflowmassgalaxies

R~5000

REQ-SRD-013 HighspectralresolutionR>=40000 R>=20000 Essential,

R~20-40K Essential Youngstars

Brightglobularclusters

REQ-SRD-021 Sciencefieldofview~2000sq.deg all-sky 1000ssq.

deg1000ssq.deg

100ssq.deg

3200(100)sq.deg ~100sq.deg ~1000sq.de

g~300sq.deg 40sq.deg 7sq.deg all-sky

REQ-SRD-022

Multiplexingatlowerresolution

~5000galaxies/sq.deg

100stargets(galaxies/GCs)/sq.deg

>5000galaxies/sq.deg

770galaxies/sq.deg

600AGN/deg

1000sgalaxies/sq.deg

REQ-SRD-023

Multiplexingatmoderateresolution

1000sstars/sq.degtog~23


few-thousandsstars/sq.deg

~5000galaxies/sq.deg

500galaxies/sq.deg

REQ-SRD-024

Multiplexingathighresolution

~100stars/sq.deg@g=16

~1000stars/sq.degtog=20.5

~1000stars/sq.degtog=20.5


REQ-SRD-025 SpatiallyresolvedspectraGoal Goal Yes

REQ-SRD-031

Spectralcoverageatlowresolution

0.37-1.5um

0.37-1.5um

0.36-1.8um

0.36-1.8um

0.36-1.8um(0.36-

0.36-1.8um

Opticalemissionlines

REQ-SRD-032

Spectralcoverageatmoderateresolution

Stronglinediagnosticsinoptical

CaTessential

CaTessential

Goal:complete

Goal:complete

Goal:complete

REQ-SRD-033

Spectralcoverageathighresolution

Stronglinesforvelocities;tagging

Stronglinesforvelocities

Chemicaltagging

Stronglinesforvelocities

REQ-SRD-034

Sensitivityatlowresolution

i=24.5 i=24.5 i=25.3 i=25/H=24 i=23.25 i=24.5

REQ-SRD-035

Sensitivityatmoderateresolution

g>20.5 g~23 i=24 i=24.5 i=24.5 r~24

REQ-SRD-036

Sensitivityathighresolution

g=16@highSNR g=20.5 g=20.5 g~22

REQ-SRD-041 Velocitiesatlowresolutionv~20km/s v~20km/s v~100km/s v~20km/s v~20km/s v~20km/s

REQ-SRD-042

Velocitiesatmoderateresolution

v~1km/s v~1km/s v~5km/s v~9km/s v~9km/sv~20km/s(10km/sgoal)

REQ-SRD-043

Velocitiesathighresolution

v<100m/s v~100m/s v~100m/s v<1km/s

REQ-SRD-044

Relativespectrophotometry

~4% Critical:3%

REQ-SRD-045

Skysubtraction,continuum

few% few% few% few% <1% <1% <1% <0.5% <0.5% <1% <1% <1%

REQ-SRD-046

Skysubtraction,emissionlines

important(CaTregion)

important(CaTregion)

critical critical critical critical critical critical

REQ-SRD-051 Accessiblesky

Platofootprint(ecliptic)

Gaiafootprint(allsky)

Gaiafootprint(allsky)

Gaia,PS1,HSCfootprint

Northernhemisphere(M31,M33,dec~+40)

LSSToverlapuseful(10000sq.deg)

NGVSfootprint;dec+12

LSSToverlapuseful(10000sq.deg);Euclid(allsky)



allskytargetdistribution

allskytargetdistribution

REQ-SRD-052 Observingefficiencymaximise maximise maximise maximise maximise maximise maximise maximise maximise maximise maximise maximise

REQ-SRD-053 ObservatorylifetimeMonitoring>=years

Monitoring>=years

Survey>=5years

Survey>=5years

Survey~100snights

Survey~fewyears

Survey~100snights

Survey~7years

Survey~100snights

Survey~100snights

Monitoring~5years

Survey~years

Calibratio

nOpe

ratio

ns

Resolvedstellarsources Extragalacticsources

Spectral

resolutio

nFocalplane

inpu

tSensitivity



4.2 IndividualRequirements

Eachsciencerequirementisdescribedindetailinthissection.Eachrequirementcontainsthefollowinginformation:

• theIDfortherequirementidentificationnumber• thenameoftherequirement• thedetailsfortherequirement• thejustificationoftherequirementwithexplicitdescriptionofitsscientific

origin,includingcross-referencetotherelevantSRO(s)andtheappropriatesectionsoftheDSC

• notesonanyotherrelevantinformationpertainingtotherequirementinordertoprovideacompleteunderstandingofitsintent.

4.2.1 REQ-SRD-011Lowspectralresolution

[REQ-SRD-011]MSEshallprovideamodewithanaveragespectralresolutionof2500≤R≤3000atopticalwavelengths(λ<950nm,TBC),withaminimumresolutionofR>2000atopticalwavelengths,andaminimumspectralresolutionofatleastR=3000(Goal:R=5000)atnearinfraredwavelengths(λ>950nm,TBC).Justification:Spectralresolutionissetbymeasurementofextragalacticredshifts[DSC-SRO-06,DSC-SRO-07,DSC-SRO-08,DSC-SRO-09]andbyAGNreverberationmapping[DSC-SRO-11]requiringnominalvelocityresolutionof100km/s.ResolutionofatleastR=3000neededintheNIRtoobservebetweenthebrightskylines[DSC-SRO-08,DSC-SRO-09;DSC-SRO-11].Notes: (i)Spectralresolutionisdefinedasλ/dλ.dλisthefullwidthathalfmaximumofaGaussianfittedtoanunresolvedspectrallineontheextractedspectrumthathasawavelengthofλ.Forarealinstrument,thedeliveredinstrumentprofilemaydiffersignificantlyfromGaussian,andinteractionswiththescienceteamwillbenecessarytoensurethatthedeliveredresolutionmeetsexpectationsintermsofscienceperformance(ii)Atopticalwavelengths,thisspectralresolutionreferstoanaveragevalue.AtNIRwavelengths(λ ≳ 950nm),thisspectralresolutionreferstoaminimumvalue(R>3000neededtoobservebetweenbrightskylinesintheNIR).(iii)Thismodewillhereafterbereferredtoas"low".Itisakeymodeofoperationthatwillaccountformostofthedarktimescience.(iv)RefertoREQ-SRD-031fortheprecisewavelengthcoverageofMSEinthismode.

4.2.2 REQ-SRD-012Moderatespectralresolution



[REQ-SRD-012]MSEshallprovideamodewithanaveragespectralresolutionof5000≤R≤7000ineachwavelengthwindow,withaminimumspectralresolutionwithineachwindowofR>4500.Justification:SpectralresolutionissetbytheneedtogetvelocitiesofthebrighteststarsintheLocalGroupwithaprecisionof1–2km/sinareasonableintegrationtime(hours)[DSC-SRO-04,DSC-SRO-05],analysisofstrongstellarlinesintheGalaxy[DSC-SRO-03],thestellarpopulationanalysisofnearbygalaxies[DSC-SRO-06,DSC-SRO-07],andbythestudyoftheIGM[DSC-SRO-10].Notes: (i)Spectralresolutionisdefinedasλ/dλ.dλisthefullwidthathalfmaximumofaGaussianfittedtoanunresolvedspectrallineontheextractedspectrumthathasawavelengthofλ.Forarealinstrument,thedeliveredinstrumentprofilemaydiffersignificantlyfromGaussian,andinteractionswiththescienceteamwillbenecessarytoensurethatthedeliveredresolutionmeetsexpectationsintermsofscienceperformance(ii)Itisexpectedthatthismodewillbeusedduringbothbrighttimeanddarktimedependingonthescience.(iii)Thismodewillhereafterbereferredtoas"moderate".(iv)RefertoREQ-SRD-032fortheprecisewavelengthcoverageofMSEinthismode.

4.2.3 REQ-SRD-013Highspectralresolution

[REQ-SRD-013]MSEshallprovideamodewithanaveragespectralresolutionof38000≤R≤42000inwavelengthwindowsatλ ≲500nm,withaminimumspectralresolutionwithinthesewindowsofR>35000(ii)anaveragespectralresolutionof18000≤R≤22000inanywavelengthwindowsatλ ≳500nm,withaminimumspectralresolutionwithinthesewindowsofR>15000(TBC).Justification:Spectralresolutionissetbystellarchemistrysciencecases,inparticulartheabilitytomeasureabundancesfromweaklinesandtoresolvelinesintheblue(whereblendingissignificant)[DSC-SRO-03].Atredderwavelengths,blendingislesssignificantandthusalowerspectralresolutionissufficient.Highvelocityprecisionisalsorequiredbystellarastronomyprograms[DSC-SRO-02,DSC-SRO-03,DSC-SRO-04]andbyexoplanetaryhoststudies[DSC-SRO-01].Notes: (i)Spectralresolutionisdefinedasλ/dλ.dλisthefullwidthathalfmaximumofaGaussianfittedtoanunresolvedspectrallineontheextractedspectrumthathasawavelengthofλ.Forarealinstrument,thedeliveredinstrumentprofilemaydiffersignificantlyfromGaussian,andinteractionswiththescienceteamwillbenecessarytoensurethatthedeliveredresolutionmeetsexpectationsintermsofscienceperformance(ii)Thetransitionbetween“blue”and“red”wavelengthsatλ ~500nmis



gradualandshouldnotbeinterpretedduringtheDesignPhaseasahardnumber.(iii)Thismodewillhereafterbereferredtoas"High".Itisakeymodeofoperationthatwillaccountforalargefractionofthebrighttimescience.(iv)RefertoREQ-SRD-033fortheprecisewavelengthcoverageofMSEinthismode.

4.2.4 REQ-SRD-021Sciencefieldofview

[REQ-SRD-021]MSEshallhaveasciencefieldofviewfromwhichtargetscanbeselectedthathasashapethatcanbetiledinaregularpatternandwhichhasanareanotlessthan1.5squaredegrees.Justification:MSEmustconductsurveysspanningareasofuptomanythousandsofsquaredegrees,thusalargefieldofviewthatcanbetiledisessentialforefficientcompletionofthesesurveys.TheS1-WcomponentofDSC-SRO-06hasdetailedplansforwhatisenvisionedasatypical,extensive,legacysurveyrequiringcovering3200squaredegrees.Weassumethatthistakestheformofasingle-passsurvey,withanexposuretimeof1hourperpointing,sufficienttoobtaingoodSNRonthefainttargets.Anefficientcompletiontimeforthissurveycomponentisestimatedtobe1yearofdarktime.Weassumeanaverageof9.9hourspernight,andahistoricalweatherimpactof2.7hourspernight(thesenumbersarebasedonSection1.2ofhttp://www.cfht.hawaii.edu/Instruments/Imaging/MegaPrime/observingstats.html).Adoptingascienceobservingefficiency(openshuttertimeonsciencetargets)of80%(seeREQ-SRD-052)implies~2100hoursofscienceobservingperyear.CompletionofS1-Win1yearofDarkTimethereforerequiresasciencefieldofviewfromwhichtargetsareselectedof1.5squaredegrees.Notes: (i)Thereismoreflexibilityintheacceptablefieldofviewcomparedtoothersciencerequirements(withanappropriatemodificationinthemultiplexingconsistentwithREQ-SRD-022,REQ-SRD-023andREQ-SRD-024);thefieldmustbesufficientlylargetoallowalargeareatobecoveredefficiently(ii)Aregularshapedfieldofviewisrequiredinordertofacilitatesurveyplanning/tiling.(iii)Thephrase"fromwhichtargetscanbeselected"impliesthatanytargetatanypositioninthesciencefieldofviewispotentiallyaccessibleforobserving(i.e.,ifaregionofthefieldofviewcannotbeaccessedforanyreason,thenthatareadoesnotcounttowardsthesciencefieldofview)(iv)Fieldofviewiscoupledtomultiplexing(REQ-SRD-022,REQ-SRD-023,REQ-SRD-024),sensitivityrequirements(REQ-SRD-034,REQ-SRD-035,REQ-SRD-036),andscienceobservingefficiency(REQ-SRD-052)sincetheproductofallofthesecomponentsdefinesthe“surveyspeed”ofMSE.

4.2.5 REQ-SRD-022Multiplexingatlowresolution



[REQ-SRD-022]Inlowresolutionmode,MSEshallbeabletoobtainthegreaterof(a)3200spectra,or(b)theequivalentofatleast0.593spectra/sq.arcmin,averagedoverthefieldofviewfromwhichtargetscanbeselected,perexposure.Justification:Lowresolutionmodewillbeprimarilyusedindarktimetostudygalaxies.Thesourcedensityofgalaxiesatz<0.2brighterthani=23is2100/sq.degree(withavarianceof~30%),or~3200per1.5squaredegrees[DSC-SRO-06;seealsoREQ-SRD-021].Thissetstheminimumfiberdensityforextragalacticstudies.Thespacedensityoffaintertargetsisevenhigher[DSC-SRO-08]anddrivesustoashighaspacedensityaspossible(ascloseto1persq.arcminaspossible).Notes: (i)0.593spectra/sq.arcmincorrespondsto3200spectraina1.5squaredegreefieldofview(thus,ifthefieldofviewincreasesbeyond1.5squaredegrees,themultiplexingshouldincreaseproportionally).(ii)Inreality,sourcesarenotsmoothlydistributed.Somepotentialtargetswillbeclosetoeachother,andtheabilitytoobservetargetsclosetogetherinthesameexposurewillincreaseefficiency.(iii)Withoutanypre-selection,thegalaxysourcedensityati<23ishigh,andthisdrivesustoashighadegreeofmultiplexingaspossible.Thereforethestatedmultiplexingisaminimumvalueandhighervaluesarepreferable(ascloseto1persq.arcminaspossible;[DSC-SRO-08]).(iv)Skyfibers(andothercalibrationfibers)arenotexplicitlyincludedinthemultiplexingrequirement.Itisenvisioned,however,thatforalmostallviablemultiplexingsolutions,100%offiberswillnotbeabletobeassignedtosciencetargets.Thus,thesefiberswillbeallocatedtoskyandothercalibrationtargets.(v)Multiplexingiscoupledtofieldofview(REQ-SRD-021),sensitivityrequirements(REQ-SRD-034,REQ-SRD-035,REQ-SRD-036),andscienceobservingefficiency(REQ-SRD-052)sincetheproductofallofthesecomponentsdefinesthe“surveyspeed”ofMSE.

4.2.6 REQ-SRD-023Multiplexingatmoderateresolution

[REQ-SRD-023]Atmoderateresolution,MSEshallbeabletoobtainthegreaterof(a)3200spectra,or(b)theequivalentofatleast0.593spectra/sq.arcmin,averagedoverthefieldofviewfromwhichtargetscanbeselected,perexposure.Justification:Thesourcedensityofgalaxiesatz<0.2brighterthani=23is~2100/sq.degree(withavarianceof~30%),or~3200per1.5squaredegrees[DSC-SRO-06;seealsoREQ-SRD-021].Thissetstheminimumfiberdensityforextragalacticstudies.Notes: (i)Moderateresolutionwillbeusedforbothgalaxystellarpopulations[DSC-SRO-06]andresolvedstarsinthenearbyUniverse[DSC-SRO-03,DSC-SRO-04,DSC-SRO-05].Galaxiessetthehighermultiplexingconstraint.(ii)0.593spectra/sq.arcmin



correspondsto3200spectraina1.5squaredegreefieldofview(thus,ifthefieldofviewincreasesbeyond1.5squaredegrees,themultiplexingshouldincreaseproportionally).(iii)Inreality,sourcesarenotsmoothlydistributed.Somepotentialtargetswillbeclosetoeachother,andtheabilitytoobservetargetsclosetogetherinthesameexposurewillincreaseefficiency.(iv)Withoutanypre-selection,thegalaxysourcedensityati<23ishigh,andthisdrivesustoashighadegreeofmultiplexingaspossible.Thereforethestatedmultiplexingisaminimumvalueandhighervaluesarepreferable.Note,however,thatthegainsofhighermultiplexingarelessthanforthelowresolutionmodesincethemoderateresolutionmodewillgenerallynotbeusedonveryfainttargets(iv)Skyfibers(andothercalibrationfibers)arenotexplicitlyincludedinthemultiplexingrequirement.Itisenvisioned,however,thatforalmostallviablemultiplexingsolutions,100%offiberswillnotbeabletobeassignedtosciencetargets.Thus,thesefiberswillbeallocatedtoskyandothercalibrationtargets.(v)Multiplexingiscoupledtofieldofview(REQ-SRD-021),sensitivityrequirements(REQ-SRD-034,REQ-SRD-035,REQ-SRD-036),andscienceobservingefficiency(REQ-SRD-052)sincetheproductofallofthesecomponentsdefinesthe“surveyspeed”ofMSE.

4.2.7 REQ-SRD-024Multiplexingathighresolution

[REQ-SRD-024]Athighresolution,MSEshallbeabletoobtainthegreaterof(a)1000spectra,or(b)theequivalentofatleast0.185spectra/sq.arcmin,averagedoverthefieldofviewfromwhichtargetscanbeselected,perexposure.Justification:HighresolutionmodewillbeusedprimarilyinbrighttimetostudythechemodynamicsofstarsintheGalaxy.ThesourcedensityofthickdiskandhalostarsathighGalacticlatitudeinthecriticalmagnituderange17<g<21is~700persquaredegree,or~1000per1.5squaredegree(Besançonmodel;Robinetal.2003,A&A,409,523);[DSC-SRO-03];seealsoREQ-SRD-021).Notes: (i)Thebrightmagnitudelimitof17usedintheJustificationensuresthatalltargetsforMSEchemicalabundancestudiesaretoofainttobestudiedusing4m-classfacilities.(ii)MSEfocusesonstudiesofthethickdiskandhalosinceexcellentstudiesofthethindiskcanbeaccomplishedusing4m-classfacilities.(iii)Inreality,sourcesarenotsmoothlydistributed.Somepotentialtargetswillbeclosetoeachother,andtheabilitytoobservetargetsclosetogetherinthesameexposurewillincreaseefficiency.(iv)0.185spectra/sq.arcmincorrespondsto1000spectraovera1.5sq.degreefieldofview(thus,ifthefieldofviewincreasesbeyond1.5squaredegrees,themultiplexingshouldincreaseproportionally).(v)Skyfibers(andothercalibrationfibers)arenotexplicitlyincludedinthemultiplexingrequirement.Itisenvisioned,however,thatforalmostallviablemultiplexingsolutions,100%offiberswillnotbeabletobeassignedtosciencetargets.Thus,thesefiberswillbeallocatedtoskyandothercalibrationtargets.(vi)



Multiplexingiscoupledtofieldofview(REQ-SRD-021),sensitivityrequirements(REQ-SRD-034,REQ-SRD-035,REQ-SRD-036),andscienceobservingefficiency(REQ-SRD-052)sincetheproductofallofthesecomponentsdefinesthe“surveyspeed”ofMSE.

4.2.8 REQ-SRD-025Spatiallyresolvedspectra

[REQ-SRD-025]DuringthelifetimeofMSE,MSEshallbeabletoprovideamulti-objectintegralfieldcapability,toobtainspatiallyresolvedspectraldataontargetsthatsubtendmanyarcsecondsonthesky,withparametersTBD.Justification:MSEwillhavethecapabilitytoprovidemulti-objectIntegralFieldUnitstoaddresskeysciencecasesforspatiallyresolvedtargets([DSC-SRO-12],DSC–Sections3.3.3.;4.4.2–4.4.5).Notes: (i)TheIFUmoderequiresdetailedanalysistodecideupontheoptimalarrangement(especially,numberofspectrapertargetversusnumberoftargets).(ii)TheIFUmodeisnotanticipatedasafirstlightcapability.Atfirstlight,allowancemusthavebeenmadefortheabilitytoincludethiscapabilityduringthelifetimeofMSE(attheveryleast).

4.2.9 REQ-SRD-031Spectralcoverageatlowresolution

[REQ-SRD-031]Inthelowresolutionmode,MSEshallprovidethefollowingtwo,critically-sampled,spectralcoverageoptions:(a)continuousspectralcoveragefrom360nmto1300nm,inasingleexposure(the“J-band”mode),and(b)continuouscoveragefrom360nmto950nm(TBC)andfrom1500to1800nminasingleexposure(the“H-band”mode).(Goalandlifetimerequirement:optical+J-band+H-bandsimultaneously)Justification:(i)MSEmusthavegoodsensitivitytoOII3727Å[DSC-SRO-06,DSC-SRO-07,DSC-SRO-10].(ii)Alargenumberofchemicalspecieshavelinesshortwardof400nm,andsensitivitytothesefeaturesisimportantforestimatesofthemetallicity[DSC-SRO-06,DSC-SRO-07].(iii)Inthelowresolutionmode,MSEmustbeabletoderiveredshiftsandidentifythesamefeaturesingalaxiesatarangeofredshifts[DSC-SRO-08].TheNIRcut-offisthereforesetbytheredshiftouttowhichcertainfeaturescanbeidentified.Inpractice,thecut-offissetbytechnicalandfinanciallimitations,notbyclearsciencethresholds.(iv)JandHarerequiredforthehighredshiftobjects[DSC-SRO-08,DSC-SRO-09,DSC-SRO-10,DSC-SRO-11].Ideally,bothbandswillbeobservedsimultaneously,althoughatfirstlightitisacceptableifonlyasinglebandisobservableatonce.



Notes: (i)Duetothedifficultiesofoptimizationofopticsto360nm,andtheinevitablecompromisesthiswillentailforperformanceatotherwavelengths,MSEwillbesensitiveto360nmbutitsperformancewillbeoptimizedforwavelengthslongerthan370nm.MSEwillconductitsprimaryscientificanalysisonwavelengthslongerthan370nm,withsomelimitedscienceanalysisoccurringforwavelengthsbetween360–370nm.(ii)Thewavelengthcut-offsintheNIR(endofJ-band,1300nm;Hband,1500–1800nm)areapproximatevaluesonly,andsomesmallvariationaroundthesenumbersispotentiallyacceptableafterconsultationwiththeScienceTeam,ifsuchachangeleadstoanoptimaltechnicalsolution. [Comments:DuringtheConceptualDesignthefeasibilityofincludingtheH-band(orsomefractionthereof)willbeexamined.Oncethecostandriskofthiscapabilityareknown,changesinthisrequirementmaybesought,ifnecessary]

4.2.10 REQ-SRD-032Spectralcoverageatmoderateresolution

[REQ-SRD-032]Inthemoderateresolutionmode,MSEshallprovidecoverageinoneormorespectralwindowsselectedfromtherange360–950nm(TBC)thattogetherprovideatotalbandwidthofatleast250nmandthatcontainthewavelengthinterval845–885nm.Justification:(i)Moderatespectralresolutionisrequiredforstellarpopulationanalysesofunresolved(brighter)galaxies[DSC-SRO-06]andforchemicalabundance[DSC-SRO-03]andradialvelocitystudies[DSC-SRO-04,DSC-SRO-05]offaintstars,inwhichitmaybeusedinconjunctionwiththehighresolutionmode.(ii)Broadwavelengthcoverageisrequiredinordertoaccessasmanyspectralfeaturesaspossibletosupporttheseanalyses.(ii)Theregionfrom845–885nmisrequiredtoaccesstheCaIITripletregion[8498,8542,8662Å],MgI8806Å(gravity-sensitive),andalargenumberofFelinesandα-elements,necessaryfornearbyresolvedstellarpopulationanalysis[DSC-SRO-05].Notes: (i)Duetothedifficultiesofoptimizationofopticsto360nm,andtheinevitablecompromisesthiswillentailforperformanceatotherwavelengths,MSEwillbesensitiveto360nmbutitsperformancewillbeoptimizedforwavelengthslongerthan370nm.(ii)Thewavelengthcoverageneednotbecontinuous.

4.2.11 REQ-SRD-033Spectralcoverageathighresolution

[REQ-SRD-033]Inthehighresolutionmode,MSEshallprovidecriticallysampledspectralcoverageinatleastthree,non-overlapping,wavelengthwindowsselectedfromtherange360–900nm(TBD)thatcanbeadjustedoverthelifetimeofMSE.Thewavelengthcoverageineachwindowwillbeatleast!!

!"× !""""

!,whereλ! isthecentralwavelength



ofthewindowandRisthespectralresolutionofthewindowatλ! ,andatleasthalfofthesewindowswillbesituatedatλ! ≲500nm.Justification:Inthehighresolutionmode,MSEmustbeabletomeasuretheabundancesofalargenumberofchemicalspeciesthataredistributedacrosstheopticalregionwithaconcentrationtowardsbluerwavelengths[DSC-SRO-03].Multiplewavelengthwindowsarethereforerequiredinordertoaccessarangeofchemicalspecies.Notes: (i)Inthehighresolutionmode,allmajorscientificallyinterestingfeaturesathighresolutionareatwavelengthsshorterthan900nm.(ii)Itisexpectedthatthespectralcoverageofthewindowswillbeaslargeasispossiblegivenlargeformatdetectors.(iii)Duetothedifficultiesofoptimizationofopticsto360nm,andtheinevitablecompromisesthiswillentailforperformanceatotherwavelengths,MSEwillbesensitiveto360nmbutitsperformancewillbeoptimizedforwavelengthslongerthan370nm.(iv)Ongoinginteractionsbetweenthespectrographdesignteamandthescienceteamiscriticaltoensurethatthefinalwavelengthwindowsbestsampletherangeofchemicalspeciesofmostrelevancetothescienceprograms.Thediversityofspeciesaccessible,thediversityofsciencecasesaddressedwithinDSC-SRO-03,andtherateofprogressinthisfield,meansthatamoreexactdefinitionofthepositionandwavelengthcoverageofthehighresolutioncapabilityispremature.[Comments:DuringtheConceptualDesignPhase,thespectralcoverageperarmandthecostperarmwillbeinvestigated.Onceknown,theScienceTeamwilladviseonthenumberofarmsthatarerequiredforthatdesignandtheProjectOfficewilldecideifthisrequirementshouldbemodified.]

4.2.12 REQ-SRD-034Sensitivityatlowresolution

[REQ-SRD-034]Inthelowresolutionmode,anextractedspectrumfromMSEtakenintheobservingconditionsdescribedbelowshallhaveasignaltonoiseratioperresolutionelementatagivenwavelengththatisgreaterthanorequaltotwofora1hourobservationofapointsourcewithafluxdensityof9.1x10-30ergs/sec/cm2/Hzatthatwavelength,forallwavelengthslongerthan400nm.Between370–400nm,theSNRshallnotbelessthanoneatanywavelength.Theobservingconditionsinwhichthisrequirementshallbemetcorrespondtoaskybrightnessof20.7mags/sq.arcsecintheV-bandatanairmassof1.2,andadeliveredimagequalityatthatairmassof0.6arcsecondsfullwidthathalfmaximumintherband.Justification:VariousproposedredshiftsurveysforMSEallrequiresignaltonoiseratiosofafewtoderivesufficientlyaccurateredshiftsforintrinsicallyfainttargets.TheLSSTsinglevisitdepthisi=24,andMSEshouldaimtoefficientlymeasureredshiftsforthese



targets[DSC-SRO-06].ThismagnitudelimitalsocorrespondstothelimitingmagnitudeforavolumeatmoderateredshiftinDSC-SRO-08;closervolumesinDSC-SRO-08canbeprobedmoreefficiently,andmoredistantvolumeswillstillbeabletobeprobedmoderatelyefficientlythroughtheuseoflongerexposures.Notes: (i)ThisrequirementcorrespondstoanobservationofanastrophysicalsourcewithamonochromaticABmagnitudeofm=24intypicalobservingconditions.(ii)A“deliveredimagequalityof0.6arcseconds”correspondstotheIQasseenonthetelescope'sopticalfocalsurface(i.e.,includingatmosphericcomponentsaswellasdomeseeingeffectsandtelescopeoptics).(iii)Relevantdatafilesrelatingtotheemissionandtransmissionoftheatmospherecanbeaccessedathttp://mse.cfht.hawaii.edu/docs/mse-science-docs/SRD/(iv)Sensitivityiscoupledtothefieldofview(REQ-SRD-021),multiplexing(REQ-SRD-022,REQ-SRD-023,REQ-SRD-024)andscienceobservingefficiency(REQ-SRD-052),sincetheproductofallofthesecomponentsdefinesthe“surveyspeed”ofMSE.

4.2.13 REQ-SRD-035Sensitivityatmoderateresolution

[REQ-SRD-035]Inthemoderateresolutionmode,anextractedspectrumfromMSEtakenintheobservingconditionsdescribedbelowshallhaveasignaltonoiseratioperresolutionelementatagivenwavelengththatisgreaterthanorequaltotwofora1hourobservationofapointsourcewithafluxdensityof1.4x10-29ergs/sec/cm2/Hzatthatwavelength,forallwavelengthslongerthan400nm.Between370–400nm,theSNRshallnotbelessthanoneatanywavelengthintherelevantwindow.Theobservingconditionsinwhichthisrequirementshallbemetcorrespondtoaskybrightnessof20.7mags/sq.arcsecintheV-bandatanairmassof1.2,andadeliveredimagequalityatthatairmassof0.6arcsecondsfullwidthathalfmaximumintherband.Justification:VariousproposedgalaxyandstellarsurveysforMSEallrequiresignaltonoiseratiosofafewtoderivesufficientlyaccuratevelocitiesforintrinsicallyfainttargets.Specifically,DSC-SRO-06(S1-Dcomponent)andDSC-SRO-07requiretheefficientobservationofi=23.5targetsforthederivationofvelocitiesaccuratetoafewtensofkm/sforgalaxygroupsandclusters.Further,DSC-SRO-05requiresbeingabletoefficientlymeasurevelocitiesforstarsatleastonemagnitudebelowthetipoftheredgiantbranchattheapproximatedistanceofM31(correspondingtoi~23.5).Notes: (i)ThisrequirementcorrespondstoanobservationofanastrophysicalsourcewithamonochromaticABmagnitudeofm=23.5intypicalobservingconditions.(ii)A“deliveredimagequalityof0.6arcseconds”correspondstotheIQasseenonthetelescope'sopticalfocalsurface(i.e.,includingatmosphericcomponentsaswellasdomeseeingeffectsandtelescopeoptics).(iii)Relevantdatafilesrelatingtothe



emissionandtransmissionoftheatmospherecanbeaccessedathttp://mse.cfht.hawaii.edu/docs/mse-science-docs/SRD/(iv)Sensitivityiscoupledtothefieldofview(REQ-SRD-021),multiplexing(REQ-SRD-022,REQ-SRD-023,REQ-SRD-024)andscienceobservingefficiency(REQ-SRD-052),sincetheproductofallofthesecomponentsdefinesthe“surveyspeed”ofMSE.

4.2.14 REQ-SRD-036Sensitivityathighresolution

[REQ-SRD-014]InthehighresolutionmodeinanywavelengthwindowobservedoverthelifetimeofMSE,anextractedspectrumfromMSEtakenintheobservingconditionsdescribedbelowshallhaveasignaltonoiseratioperresolutionelementatagivenwavelengththatisgreaterthanorequaltotenfora1hourobservationofapointsourcewithafluxdensityof3.6x10-28ergs/sec/cm2/Hzatthatwavelength,forallwavelengthsintherelevantwindowlongerthan400nm.Between370–400nm,theSNRshallnotbelessthanfiveatanywavelengthintherelevantwindow.Theobservingconditionsinwhichthisrequirementshallbemetcorrespondtoaskybrightnessof19.5mags/sq.arcsecintheV-bandatanairmassof1.2,andadeliveredimagequalityatthatairmassof0.6arcsecondsfullwidthathalfmaximuminthegband.Justification:HighSNRobservationsofmoderatelyfainttargetsarerequiredfortheefficientmeasurementofvelocities(especiallyDSC-SRO-04)andchemicalcompositionofstarsintheMilkyWay[DSC-SRO-02,DSC-SRO-03)fainttargetsinordertorobustlyderivechemicalabundanceinformation.G=20isthenominalmagnitudelimitofGaiasources,forwhichMSEmustbeabletoconductefficientobservations.Notes: (i)ThisrequirementcorrespondstoanobservationofanastrophysicalsourcewithamonochromaticABmagnitudeofm=20intypicalobservingconditions.(ii)A“deliveredimagequalityof0.6arcseconds”correspondstotheIQasseenonthetelescope'sopticalfocalsurface(i.e.,includingatmosphericcomponentsaswellasdomeseeingeffectsandtelescopeoptics).TheIQisdefinedinthegband(incontrasttoREQ-SRD-034andREQ-SRD-035)sincethemajorityofthekeysciencemeasurementsinthehighresolutionmodewillbemadeshortwardof500nm(iii)Relevantdatafilesrelatingtotheemissionandtransmissionoftheatmospherecanbeaccessedathttp://mse.cfht.hawaii.edu/docs/mse-science-docs/SRD/(iv)Sensitivityiscoupledtothefieldofview(REQ-SRD-021),multiplexing(REQ-SRD-022,REQ-SRD-023,REQ-SRD-024)andscienceobservingefficiency(REQ-SRD-052),sincetheproductofallofthesecomponentsdefinesthe“surveyspeed”ofMSE.

4.2.15 REQ-SRD-041Velocitiesatlowresolution



[REQ-SRD-041]Foranyobjectwithaknownvelocity,observedatmultipleepochsbyMSEwithuptoa5yearcadencewithasignaltonoiseratioperresolutionelementof5atlowspectralresolution,thecontributionfromMSEtothermsdifferencebetweentheknownvelocityoftheobjectandthemeasuredvelocityoftheobjectshallbelessthanorequalto20km/s,andshallhavenosystematicdependenceonthewavelengthregionofthespectrumthatisusedtothelevelof5km/s(TBC)(providedsuitablefeaturesexist,i.e.,anystrongabsorptionoremissionlines).Justification:MSEmustbeabletomeasureaccurateredshiftsofmoderatelyfaintgalaxies,especially(butnotonly)forclusteringstudies[DSC-SRO-06,DSC-SRO-07,DSC-SRO-09,DSC-SRO-11).Notes:ThisvelocityaccuracyistheintrinsicvelocityofthismodeatthisSNR(𝑑𝑣 =!!

!"#~ (3×10!/3000)/5 = 20km/s)andrequiresthattherearenosystematicerrors

inthewavelengthcalibrationacrossthewavelengthrange.NotealsothatthevelocityprecisionscalesinverselyasSNR,andthechosen[velocity–SNR]combinationusedtodefinetherequirementdoesnotnecessarilyrepresenttheexpectedvaluesforallobservations.

4.2.16 REQ-SRD-042Velocitiesatmoderateresolution

[REQ-SRD-042]Foranyobjectwithaknownvelocity,observedatmultipleepochsbyMSEwithuptoa5yearcadencewithasignaltonoiseratioperresolutionelementof5atmoderatespectralresolution,thecontributionfromMSEtothermsdifferencebetweentheknownvelocityoftheobjectandthemeasuredvelocityoftheobjectshallbelessthanorequalto10km/s,andshallhavenosystematicdependenceonthewavelengthregionofthespectrumthatisusedtoalevelof1km/s(TBC)(providingsuitablefeaturesexist,i.e.,anystrongabsorptionoremissionline).Justification:MSEmustbeabletomeasureaccuratevelocitiesformoderatelyfaintstarsintheLocalGroup,especiallyindwarfgalaxiesandstellarstreams,whichhavetypicalvelocitiydispersionsoforder10km/s[DSC-SRO-04,DSC-SRO-05].Notes:ThisvelocityaccuracyistheintrinsicvelocityofthismodeatthisSNR(𝑑𝑣 =!!

!"#~ (3×10!/6000)/5 = 10km/s)andrequiresthattherearenosystematicerrorsin

thewavelengthcalibrationacrossthewavelengthrange.NotealsothatthevelocityprecisionscalesinverselyasSNR,andthechosen[velocity–SNR]combinationusedtodefinetherequirementdoesnotnecessarilyrepresenttheexpectedvaluesforallobservations.



4.2.17 REQ-SRD-043Velocitiesathighresolution

[REQ-SRD-043]Foraradialvelocitystandardstar,observedatmultipleepochsbyMSEwithuptoa5yearcadencewithasignaltonoiseratioperresolutionelementof30athighspectralresolution,thecontributionfromMSEtothermsdifferencebetweentheknownvelocityoftheobjectandthemeasuredvelocityoftheobjectshallbelessthanorequalto0.1km/s.Justification:MSEmustbeabletomeasureprecisionvelocitiesforstellarmonitoringprogramsincludingplanet-hostingsystems[DSC-SRO-01,DSC-SRO-02,DSC–Section2.2.1].Notes: (i)ThehighresolutionmodeofMSEhasdifferentspectralresolutionlong-ward(R=20K)andshort-ward(R=40K)of500nm.Itisprobable,therefore,thatthisvelocityaccuracywillbeachievedmosteasilyshort-wardof500nm.Itisexpectedthatinmeetingthisrequirement,acomparablevelocityaccuracy(adjustedforspectralresolution)willalsobeachievablelong-wardof500nm.(ii)Thisvelocityaccuracyis

higherthanthe"intrinsic"accuracyofthismode(𝑑𝑣 =!!

!"#~ (3×10!/40000)/30 =

250m/s)andwillrelyontheuseofmultiplelinessimultaneouslytoderivevelocities.

4.2.18 REQ-SRD-044Relativespectrophotometry

[REQ-SRD-044]Foraspectrophotometricstandardstar,observedinthelowresolutionmodeatmultipleepochsbyMSEwithuptoa5yearcadencewithasignaltonoiseratioperresolutionelementof30,thermsvariationintheratiooffluxesmeasuredinanytwowavelengthintervalsshallbelessthan3%ofthemeanmeasuredvalue.Justification:ThisrequirementisspecificallynecessaryforAGNreverberationmappingstudies[DSC-SRO-11];spectrophotometryisalsorequiredforstellarpopulationstudiesofnearbygalaxiesatlowandmoderatespectralresolution[DSC-SRO-06,DSC-SRO-07].ItisanticipatedthatmeetingthisspecificrequirementforDSC-SRO-11willalsoallowMSEtosatisfythespectrophotometricneedsofDSC-SRO-06andDSC-SRO-07.Notes: (i)Relativespectrophotometryisdefinedastheratiobetweentwofluxes.(ii)Weanticipatetestingthisrequirementbyobservingmanyspectrophotometricstandardsinmanyfieldsovermultipleepochs.Afterarelativefluxcorrection,thermsvariationofthedifferencebetweentheactualrelativefluxofthetargetandthemeasuredrelativefluxvaluesshouldbelessthanorequalto3%.(iii)Sincethisrequirementisquitecomplexindefinition,analternativedraftingofREQ-SRD-044,expressedmathematically,isthefollowing:



Forasingleobservation,n,ofaspectrophotometricstar(withR=3000andSNR/resolutionelement>30),wecandefineaquantity𝐹!suchthat

𝐹! = 𝑓 𝜆 𝑑𝜆!!

!!

𝑓 𝜆 𝑑𝜆!!!!

Here,𝑓 𝜆 isthespectrumasafunctionofwavelength 𝜆 ,and(𝜆!, 𝜆!) and(𝜆!, 𝜆!) definetwowavelengthintervals.ForasetofNobservationsofthissamestarandwiththesamewavelengthintervals,wecandefinethemeanquantity𝐹andthestandarddeviation𝜎! suchthat

𝐹 = 𝐹!!

!!!

𝑁

𝜎! = ( 𝐹! − 𝐹 )!!

!!!𝑁 − 1

Ourspectrophotometricrequirementrequiresthat:

𝜎!𝐹

≤ 0.03

4.2.19 REQ-SRD-045Skysubtraction,continuum

[REQ-SRD-045]Inwavelengthintervalsfreefromairglowemission-linecontaminationandstrongtelluricabsorption,MSEshallallowforremovaloftheskyfluxwitharoot-mean-squareerroroflessthan0.5%oftheskyflux,atallwavelengths(TBC).Justification:MSEmustroutinelyobtainspectraofveryfainttargets,especially(butnotonly)inthelowresolutionmode(especially,DSC-SRO-08).Systematicerrrorsintheskysubtractionleadtoaneffective“limitingmagnitude”,belowwhichdatawillbeunreliable.ThisissummarizedinDSC-SRO-08,whichaimstotargetsomeofthefaintestsystems.Inordertomakereliablemeasurementsofsourcesthataretypically25thmagnitudeinanyband(24thmagnitudeinHband)(seeDSC-SRO-08)requires0.5%accuracyinskysubtractiongiventypicaldarktimeskyvaluestoreachanoiseequivalenterrorofatleast1(thatis,themeasuredfluxinapixelwillhaveequalcontributionsfromthesciencesourceasfromthesky).



Notes:(i)Thisispushingthelimitsofthebestskysubtractionusingfibersthatcancurrentlybeachieved.(ii)Requiresadvancedanalysis(e.g.PrincipalComponentAnalysis);SeeSharp&Parkinson2010,MNRAS,408,2495.(iii)SeealsotheMSEOperationalConceptDocument[RD-02]andtheMSEObservatoryTechnicalNoteonSkySubtractionAccuracyTN005[RD-03].(iv)Higherskysubtractionaccuracy(pushingto0.1%)ishighlydesireable.

4.2.20 REQ-SRD-046Skysubtraction,emissionlines

[REQ-SRD-046]MSEshallachieveaskysubtractionaccuracyforatmosphericairglowemission-linessuchthatthemeanresidualerrorforspectralpixels,within1resolutionelementofknownatmosphericemission-lines,is<1.5times(TBC)thePoissonlimitindicatedbythepropagatedvariancespectrumforeachresolutionelement.Justification:ThisfollowsfromthesamejustificationforREQ-SRD-045,butisappropriateforregionswithbrightskylines.Notes:(i)Thisispushingthelimitsofthebestskysubtractionusingfibersthatcancurrentlybeachieved.(ii)Requiresadvancedanalysis(e.g.PrincipalComponentAnalysis);SeeSharp&Parkinson2010,MNRAS,408,2495(iii)thedefinitionofskysubtractioninareasofbrightskylinescanbeasourceofconfusionintheliterature,andwefollowthedefinitionsgivenbySharp&Parkinson2010,MNRAS,408,2495.

4.2.21 REQ-SRD-051Accessiblesky

[REQ-SRD-051]MSEshallconductitsprimaryscienceobjectivesonastrophysicaltargetslocatedatdeclinationsgreaterthan-30degrees,andwillthereforemeettheScienceRequirementsinthisdeclinationrange.Justification:Inadditiontonortherntargets,MSEmustbeabletoaccessalargefractionofthesouthernhemispheretofollowupsurveyfacilitiesbasedinthesouth,especiallyLSSTandSKA(seediscussioninDSC–Section1.6).Adeclinationof-30degreesastheprimarylimitcorrespondstoaccessingfully50%ofthesouthernhemisphere.ThiscorrespondstoaccessinghalfofthemainLSSTfootprintandtwo-thirdsoftheSKAfootprint.AccesstotheLSSTareaisrequiredforsomeSROsduetothequality,extentandhomogeneityofphotometricdataavailable,especiallyforDSC-SRO-06,DSC-SRO-08,DSC-SRO-09andDSC-SRO-11.Notes: (i)Alimitednumberofscienceobservationswilloccurforastrophysicaltargetslocatedatdeclinationsbetween-30and-40degrees,butMSEisnotrequiredtomeetthesciencerequirementsinthisrange(ii)Thisrequirementdoesnotsupersede



requirementsthatexplicitlyspecifyanairmassorzenithdistance(e.g.,thesensitivityrequirements,REQ-SRD-034/035/036,areonlyexpectedtobemetatanairmassof1.2asdescribedinthoserequirements)(iii)Adeclinationof-40degreescorrespondstoanairmassof2,andadeclinationof-30degreescorrespondstoanairmassof~1.55

4.2.22 REQ-SRD-052Scienceobservingefficiency

[REQ-SRD-052]MSEshallhaveanaveragescienceobservingefficiencyofatleast80%.Scienceobservingefficiencyisdefinedastheratiooftimespentduringthenightobservingsciencetargets(openshuttertime),comparedtothetimespendduringthenightconductingallotheractivitiesinwhichthetelescopeisnotcollectingphotonsfromasciencetarget.Allothernight-timeactivitiesincludetimespentconfiguringthetelescopeorinstrument,reading-out,observingcalibrationexposures,otheroverheads,scheduledorunscheduledengineeringtime,etc.Losesduetoweatherareexcludedfromthecalculationofscienceobservingefficiency.Justification:TheaveragelengthofanightatMaunakeais9.9hours,andthehistoricalaverageoftheimpactofadverseweatheris2.7hourspernight(usingthenumbersfromCFHTthatcanbefoundinSection1.2ofhttp://www.cfht.hawaii.edu/Instruments/Imaging/MegaPrime/observingstats.html).Thisimpliesthereare2628hoursofpotentialscienceobservingtimeperyear.InordertocompletethemultipleScienceReferenceObservationsinareasonabletime,ahighscienceobservingefficiencyiscritical.Forexample,thecompletionoftheS1-WcomponentofDSC-SRO-06(whichisenvisionedasatypical,extensive,legacysurveyrequiringcovering3200squaredegrees)within1yearofDarkTimerequiresan80%scienceobservingefficiency(seealsoREQ-SRD-021).Notes: (i)AhighvalueofscienceobservingefficiencyiscriticaltotheoverallsuccessofMSE.AnyincreasesinthevalueofthisquantityoverandabovetherequirementwillproducesignificantfinancialsavingsandincreasedscienceimpactfortheObservatory.(ii)SciencecalibrationexposuresarecriticaltothescientificsuccessofMSE.However,forthepurposeofdefiningthisrequirement,theyareconsideredasoverheads,althoughthisdoesnotreflectontheiroverallimportancetothesuccessoftheObservatory(iii)Scienceobservingefficiencyiscoupledtothefieldofview(REQ-SRD-021),multiplexing(REQ-SRD-022,REQ-SRD-023,REQ-SRD-024)andsensitivityrequirements(REQ-SRD-034,REQ-SRD-035,REQ-SRD-036),sincetheproductofallofthesecomponentsdefinesthe“surveyspeed”ofMSE.ThecurrentjustificationofScienceobservingefficiencyiscoupleddirectlytoREQ-SRD-021.

4.2.23 REQ-SRD-053Observatorylifetime



[REQ-SRD-053]MSEshallbeabletooperateforatleast20years.Justification:Excludingmonitoringsurveys,thelongestdurationSROsthatareabletobeconductedatfirstlight(Brighttime–DSC-SRO-03,DSC-SRO-04;Darktime–DSC-SRO-06,DSC-SRO-08)haveanestimatedtotalcompletiontimeof~10yearsaccountingforthebright/darktimesplits.TheroleoftheSROsistoidentifyhighimpactprogramsthatareexpectedtobetypicalofthescopeofMSEscience,butwhichclearlydonotdescribethetotalityofMSEsciencegiventhediversityandrangeofscienceintheDSC(muchofwhichisnotaddressedbyanyspecificSRO),aswellasthecleardifficultyindesigningprogramscontemporarytothesciencelandscapeof~2025.Therefore,weestimatetheminimumObservatorylifetimetobethetimerequiredtocompleteanoverallscienceprogramthatisatleastdoubleinscopefromwhatiscurrentlydescribedbytheSROs.Notes:–

4.2.24 REQ-SRD-061++Dataprocessingandmanagement

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