MUG HST astrometryHST Absolute Astrometry • HST is capable of extremely good relave astrometry...
Transcript of MUG HST astrometryHST Absolute Astrometry • HST is capable of extremely good relave astrometry...
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December15-16, 2016
ImprovingHSTAstrometrywithPan-STARRSandGaia
StefanoCasertanoWiththeMASTteam,theHSC/HLAteamandtheAstrometryWorkingGroup
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December15-16, 2016
HSTAbsoluteAstrometry• HSTiscapableofextremelygoodrela%veastrometry(~0.4maswith
imaging,0.2maswiththeFSG,0.03maswithspaKalscanning)• However,absoluteastrometryhastradiKonallybeenmuchlessaccurate
– Typicaluncertainty0.2”–1”(4-20KmesworsethanangularresoluKon)– Spitzer,Galex,Chandra,Herschelhaveastrometricaccuracycomparabletoor
beSerthantheirangularresoluKon• TwokindsofAstrometry:
– “Apriori”(blindpoinKng):determinedfromtheFineGuidanceSensorsacquiringthedesiredGuideStars• Availableforallexposures(withcaveatswhentargetacquisiKonmaneuversareused)• Limitedbyseveralfactors
– “Aposteriori”:determinedfrommatchingsourcesfoundineachimagewithexternalcatalogs• Mostlyavailableforcameraswith~1’FOVorlarger(WFPC2,ACS,WFC3,NIC3,STIS)• Cross-matchingmaybedifficultifwavelengthsmismatched(e.g.,UVimages)• Occasionallyfewornosourcesavailable• Accuracylimitedbyexternalcatalog–typically0.1”
• UnKlrecently,onlyaprioriastrometryavailablethroughnormalHSTarchive(STScI,ESAC,CADC)
• WorkingGroupledbyMikeFalltoimprovethissituaKon
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Aprioriastrometry
• AprioriastrometricinformaKondependsonachainofcalculaKons1. AbsoluteposiKonofGuideStars2. GeometricsoluKonforFGS=>
astrometryofFGSreferencepoint3. CalibraKonofFGSposiKoninHST
focalplane=>astrometryofHSTreferencepoint
4. CalibraKonofobservinginstrumentinHSTfocalplane=>astrometryofinstrumentreferencepoint
5. CalibraKonofgeometricdistorKoninsideinstrument=>astrometryofeachpixelindetector
• ThelimiKngqualityisin1.(absoluteGSposiKons)and3.minus4.(onlydifferencebetweenFGSandinstrumentposiKonmaSersforfinalastrometry)
• TransformaKons2.and5.areknownaccurately(tobeSerthanafewmas)
TargetposiKon
GuideStars
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AprioriAstrometry(2)
• UnKl2005,posiKonwerebasedontheoriginalGuideStarCatalog(GSC),obtainedfrom“quickV”plates– Nominalerror1”/coordinate(rms),withfrequentoutliersupto3”– ModesteffortputinfocalplanecalibraKon(GSCerrorsdominant)
• AferconversiontoGSC2coordinates(2005)andimprovedFGScalibraKon(2007),typicalerrors0.15”-0.25”/coordinate– LedtoincreasedefforttomaintainfocalplanecalibraKon
GuidestarseparaKonerrorsbeforeandaferupdates
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FocalplanecalibraConisdifficulttomaintain
• FGSposiKonsevolvewithKme– Changesupto0.2”/year– CalibraKoniscomplex,Kme-consuming– Typicallyexecutedevery2years
• MorefrequentexecuKonshavereducedbenefitsbecauseofGSerrors– Otherinstrumentsalsomovetoasmallerextent
• WithGaiacoordinatesforGS,dominanterrorisfocalplanesoluKon– Focalplaneimprovementshighlydesirable
A,B,C,D,E:FGSAlignmentCalibraKonsMid-2009:ServicingMission(COS,WFC3)
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Determiningaposterioriastrometry
• Matchingconceptuallysimple– IdenKfysourcesinHSTimage– Cross-matchtoreferencecatalog(tradiKonally2MASS,GSC2)– Adjust(3-parameterfit)toimproveHSTastrometry– InternalgeometricdistorKonknowntohighaccuracy(sub-mas)
• TypicalWFC3,ACSimagesincludeseveral(2MASS)totens(GSC2)ofmatchesathighgalacKclaKtude– PotenKalissuesinsomecases
• Complexregionswithdiffuse,parKallyresolvedemission,orclosepairs– “Source”hasdifferentmeaningforHST,ground
• ObservaKonsinUVornarrow-bandfilters– Wavelengthmismatchproducesdifferentsources
– Inprinciple,astrometrylimitedprimarilybyreferencecatalogaccuracy• However,sourcematchingisnotincludedinstandardHSTprocessing
pipeline– HubbleLegacyArchive(HLA)post-processinghasbulkupdatedastrometry(since~2009)– Analysisshowedgoodoverallquality,occasionallarge(~1”)errors
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MatchingsourcesinHLAHLAdisplayscreen(startfromhSp://hla.stsci.edu)OneACSfield(partof4-imageobservaKon)Program10581:Galaxyoverdensityatz>1.5,PIShapley
ZoomintoshowsourcematchesRedcircles:GSC2(~30matches)Greencircles:2MASS(~8matches)Astrometryupdatedfrommatches
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December15-16, 2016
TheHubbleSourceCatalog• Startedin2012toobtainhomogeneoussourceinformaKonacrossmost
HSTdata(Whitmore,Lubow,Budavari,White,etal)• SourcesmatchedacrossHSTimages
– SubstanKalimprovementinrelaKveastrometryacrossmulKpleimages• Backgroundcatalog(PanSTARRSifavailable)tosetabsoluteastrometry• UpdatedastrometrysKllnotavailableinstandardHSTprocessing
– HLAimageswillsoonbeupdatedwithHSCposiKons• Reference:Whitmoreetal,AJ2016,151,134
ImprovementinrelaKveastrometrywiththeBudavari-Lubowsourcematchingalgorithm
ImprovementinabsoluteastrometryaferHSCadjustments(mas)
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Absolute“aposteriori”astrometryinHSCnowlimitedbyreferencecatalog
• PanSTARRSdefaultsoluKonreferencedto2MASS– LargescalepaSernerror(median~56mas)– Small(single-FOV)errors~150mas– BothcanbecorrectedwithglobalsoluKonbasedonGaiaDR1
• TentaKveposiKonupdateannouncedbyPanSTARRSconsorKum;detailsunclear– Moredetailedanalysis(backtoindividualdetecKonsanddetectorgeometricdistorKon)planned
withinnext6monthsbyUSNO– Likelywillresultin<10massystemaKczonaluncertainKesonallscales
(Courtesy:V.Makarov,C.Berghea,USNO)
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ImprovingabsoluteastrometryforHSTusers(1)
StepstoobtainbeSerastrometryforHSTdataandincorporateitintheArchive:1. ImproveguidestarposiKonsandeventually
focalplanesoluKon2. Linkexternalcatalogs(especiallyPanSTARRS)
toGaia3. Matchsourcestoexternalcatalogs4. Preparedatabaseforimprovedastrometry5. TransferastrometryinformaKontoarchived
data
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December15-16, 2016
ImprovingabsoluteastrometryforHSTusers(2)
• Step1:ImproveGuideStarposiKons– Cross-matchguidestarstoGaiacatalog(completed-BrianMcLean)– CurrentlyperformingstaKsKcalanalysis– UpdatedposiKonswillbetransferredtooperaKonalguidestarcatalog
starKngspring2017– Willresultin~100mas“apriori”posiKonsforallnewHSTdata
• Step2:ObtainimprovedPanSTARRSastrometry– RequiresfinalPanSTARRSdatabase(currentlybeingtestedatSTScI)
• PlannedreleasedateisDecember19,2016– CurrentversionincludespreliminaryGaia-basedastrometry– ImprovedsoluKonatthedetectorlevel(incoordinaKonwithUSNO)
willprobablybecarriedoutinearly2017• ReducesystemaKcerrorsbelow10mas• SoluKonmaybeaffectedbyPanSTARRS-GaiaepochdifferenceunKlDR2
• Step3:MatchsourcestoPanSTARRSorotherexternalcatalogs– SameprocessasusedforHubbleSourceCatalog– Expectedtoachieveabsoluteastrometryupto~10masformostHST
imagingdata(dependingonnumberandbrightnessofmatches)
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Improvingabsoluteastrometry–forHSTusers(3)
• Step4:Generatedatabaseofimprovedastrometry– Includeimprovedaprioriandaposterioriastrometry– DatabasepopulatedunderscienKstsupervision– MulKpleastrometricsoluKonpossible;mayulKmatelyincludeexternal
input(e.g.,registraKonbasedonprocesingbyGOteams)– Willalsoallowinclusionofcommunity-providedastrometryforspecial
fields• DetailsofinformaKondefiniKonandpropagaKontobediscussed
• Step5:Modifypipelinetoreadastrometryfromdatabase– MulKplesoluKonsincluded;databasewillidenKfypreferredsoluKon,
butuserscanmodifythatchoice– OriginalsoluKonalsoretainedasalternate– MediaKngthroughdatabaseinsulatespipelinefrompotenKally
complexastrometricmatching,allowsforlaterregistraKon– WillenablepropagaKonofimprovedastrometrytoalldata,including
thosewithoutsourcematching– ExpectedtobecompletedatthesameKmeasStep2
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December15-16, 2016
GAIAAstrometryforMissionOperaConsTaskstatus
• GAIAcatalogavailability– DR1releasedtodatacentersSept16(dayaferpublicrelease)– Downloadedgbinfiles(36hours)
• ReadgbinfilesandloadSQLserver– LoadedSQLserverdatabase(30hours).– CreatedauxiliarytablesneededforMASTservices,createdtableindexesfor‘main’columns(48
hours)[addmorelater].– CreatedseparatecopyforMASTOpsserver
• ProvidewebservicetoreadGAIAcatalog(standardcatalogaccessmethods)– Setupupcatalogwebservices&casJobs(usingOpscopy)
• Cross-MatchGAIAwithGSC2– IniKalmatchingdone(alsomatchtoSDSSdr13,VISTAdr3,WISE)– PerformingstaKsKcalanalysis– Only50%GAIAobjectshaveGSC2match
• primarilyduetodeepermagsingalacKcplane
• Transferavailableastrometry(coordinates,propermoKons,errors)toGSC2– ExtendedGSCcatalogschematoaccommodateGAIAdata(GSC2.4.0)– ExtendedschematoaccommodateSDSSdr13andESOVISTAsurveys(newJWSTrequirementthey
arefunding)• GeneratenewversionofGSC2forOperaKons
– Spring2017
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AstrometryDatabaseforReprocessing–Taskstatus
• CreatedatabasewithallavailableastrometricinformaKonforeveryHST(JWST)observaKon– Guidestars,poinKngcoordinates,astrometricsoluKons,wcskeywords
• RIAassigned– EsKmatedstartJan/Feb2017– 50%effortfor6months
• GetheaderlettoolsandrecipesfromSSB– CreateheaderletsforallexisKngHSTdatasetsfromon-linecache– CreateheaderletsbasedonHLA/HSC– ComputeastrometricupdatestoheaderletsbasedonGAIAastrometry
• DominantGSpoinKngupdate(zeropointshif)• PairGSpoinKngupdate(zeropoint,rotaKon,scale)• HLA/HSCaferPS1/GAIAupdates
• ProvidewebservicetoprovideupdatedwcskeywordsforanyspecifiedobservaKontobringitontoGAIAreferenceframe
• UpdateastrometryforallobservaKonsinHST/JWSTcache• Integrateastrometricupdateintoprocessingpipeline
– Fall2017
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CanwedoevenbePer?
SomeaddiKonalavenuesforfutureimprovementinclude:• LeverageveryaccurateguidestarandsourceposiKonstoimproveHST
focalplanesoluKon– Greatlyenhancehistoricalknowledge– ReplaceexpensiveFGScalibraKonforfuturedata– WouldresultinimprovementofaprioriposiKonsforallHSTdata– Possible,butnotyetevaluatedquanKtaKvely
• UseGaiastarsdirectlywhenpossible– Lowersourcedensity,butwouldavoidlessprecisePanSTARRSmeasurements– PotenKalformas-levelastrometrywhenenoughmatchesareavailable– RequiresGaiaDR2(propermoKons)forapplicaKontopastdata
• LackofpropermoKonsisthelimiKngfactorforuseofPanSTARRSasreference• Improvesingle-sourcemeasurements
– Currentlydonewithsimplecentroiding(upto5-10maspixel-phaseerrors)– Anderson-Bellinimethodcanachieve0.5mas(1.5masinIR)forhighS/N
sources– ProposaltoreprocesssourcesforallWFC3datacurrentlyunderconsideraKon
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AddiConaltoolsforMASTusers:GaiaInterfaces
IncorporateintotheexisKngMASTinterfaces• Casjobs• Portalcross-match,catalogadvanced
searchandexport• CatalogoverlayininteracKvedisplay• Catalogwebservices(conesearchwith
outputformatopKons)
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ExampleofHSCandGaiaoverlaysonanHLAimage
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Insummary…
• AbsoluteastrometryofHSTdatawillimproveenormouslybytheendof2017– Aprioriastrometrywillgofrom300-500masto50-100masthankstoGaiaposiKonsforguidestars
– Aposterioriastrometrywillgofrom60to10masthankstoGaiacalibraKonofPanSTARRSastrometry
– TimelineforfullimplementaKon~1year• FurtherimprovementsmayyieldanaddiKonalorderofmagnitudeinboth– WillrequireGaiaDR2(withpropermoKons,late2017/early2018)forhighestprecision
• GaiadataarebeingintegratedintoMAST