December15-16, 2016

ImprovingHSTAstrometrywithPan-STARRSandGaia

StefanoCasertanoWiththeMASTteam,theHSC/HLAteamandtheAstrometryWorkingGroup

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

December15-16, 2016

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

December15-16, 2016

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

December15-16, 2016

FocalplanecalibraConisdifficulttomaintain

•  FGSposiKonsevolvewithKme–  Changesupto0.2”/year–  CalibraKoniscomplex,Kme-consuming–  Typicallyexecutedevery2years

•  MorefrequentexecuKonshavereducedbenefitsbecauseofGSerrors–  Otherinstrumentsalsomovetoasmallerextent

•  WithGaiacoordinatesforGS,dominanterrorisfocalplanesoluKon–  Focalplaneimprovementshighlydesirable

A,B,C,D,E:FGSAlignmentCalibraKonsMid-2009:ServicingMission(COS,WFC3)

December15-16, 2016

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

December15-16, 2016

MatchingsourcesinHLAHLAdisplayscreen(startfromhSp://hla.stsci.edu)OneACSfield(partof4-imageobservaKon)Program10581:Galaxyoverdensityatz>1.5,PIShapley

ZoomintoshowsourcematchesRedcircles:GSC2(~30matches)Greencircles:2MASS(~8matches)Astrometryupdatedfrommatches

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)

December15-16, 2016

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)

December15-16, 2016

ImprovingabsoluteastrometryforHSTusers(1)

StepstoobtainbeSerastrometryforHSTdataandincorporateitintheArchive:1.  ImproveguidestarposiKonsandeventually

focalplanesoluKon2.  Linkexternalcatalogs(especiallyPanSTARRS)

toGaia3.  Matchsourcestoexternalcatalogs4.  Preparedatabaseforimprovedastrometry5.  TransferastrometryinformaKontoarchived

data

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)

December15-16, 2016

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

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

December15-16, 2016

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

14

December15-16, 2016

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

December15-16, 2016

AddiConaltoolsforMASTusers:GaiaInterfaces

IncorporateintotheexisKngMASTinterfaces•  Casjobs•  Portalcross-match,catalogadvanced

searchandexport•  CatalogoverlayininteracKvedisplay•  Catalogwebservices(conesearchwith

outputformatopKons)

December15-16, 2016

ExampleofHSCandGaiaoverlaysonanHLAimage

December15-16, 2016

Insummary…

•  AbsoluteastrometryofHSTdatawillimproveenormouslybytheendof2017– Aprioriastrometrywillgofrom300-500masto50-100masthankstoGaiaposiKonsforguidestars

– Aposterioriastrometrywillgofrom60to10masthankstoGaiacalibraKonofPanSTARRSastrometry

–  TimelineforfullimplementaKon~1year•  FurtherimprovementsmayyieldanaddiKonalorderofmagnitudeinboth– WillrequireGaiaDR2(withpropermoKons,late2017/early2018)forhighestprecision

•  GaiadataarebeingintegratedintoMAST