Op#calDesignandImagePost-ProcessingfortheDirectImagingofExoplanets

TylerJ.McCabe1,Dr.BrianA.Hicks2,3,andDr.NeilT.Zimmerman31FloridaInsAtuteofTechnology:DepartmentofPhysicsandSpaceSciences

2UniversityofMarylandCollegePark:DepartmentofAstronomy3GoddardSpaceFlightCenter:Code667

ArchivalLegacyInvesAgaAonsofCircumstellarEnvironmentsFrom1997through2008,theHubbleSpaceTelescopecarriedandoperatedaNearInfraredCameraandMulAObjectSpectrometer(NICMOS)whichtookimagesofstarsbeingacAvelyformedaswellastheirproto-planetarydisks.A[er2010,advancedpost-processingtechniqueswerecreatedthatmadeuseofpreviouslyknowninstrumentPSFs.Ontopofthat,newalgorithmssuchasKarhunen-LoèveImageProjecAon(KLIP)allowedabe_erPSFsubtracAonandfainterobjectstobedetectedfromthepreviouslyreduceddata[1][2].ThisprocessledtonewlyreducedNICMOSimagesshowninFigure1.TheALICEteamcameupwithalistof29starsthathadnewobjectsthatwererevealed.TheSpectro-PolarimetricHigh-ContrastExoplanetREsearch(SPHERE)instrumentontheVeryLargeTelescope(VLT)wasthesourceofthefollowupdataforthesestars.RawSPHEREdatawasobtainedfromtheEuropeanSouthernObservatory’s(ESO)websiteandthentheinstrumentspecificdatareducAonrouAneswereruntosubtractthePSF’susingangulardifferenAalimaging(ADI).TheprocessedSPHEREdatawouldshowthateachcandidateshouldfallintooneoftwocategories:abackgroundstaroragravitaAonallyboundobject.A[erthestarhasexperiencedpropermoAonforroughly10years,backgroundstarsshouldappearfixedintheimageandgravitaAonallyboundobjectsshouldbeinthesamerelaAveposiAontothehoststar.Figure2showsacompanioncandidatethatappearstobeabackgroundobjectasitfallsalmostperfectlywithinthepredictedlocaAon.Ontheotherhand,SPHEREimagesofHD169142showedthattwoofthethreecandidateobjectsappearedtolandclosetotheirpredictedlocaAonsforabackgroundstar.However,thethirdobjectlocatedintheregionbetweenthetwopredicAons(Figure3).

Single-ModeFiberArrayToimageEarth-likeexoplanets,reducingsca_eredstarlightwithinthefieldofviewisneededtoreachadequatelevelsofcontrast.Thesecontrastsneedtobeontheorderof10-10inordertobeabletoseethelightfromtheexoplanetsthemselvesandnothaveitobscuredbythelightofthestar.ASingle-modeFiberArray(SFA)helpsreachthislevelofoff-axiscontrast,whichintheoryoutperformswhatisachievablewithapinholearrayusedinacomparablemanner[3].Figure4showstheZemaxlayoutoftheSFAandcomplexamplitudecontrolofthesingle-modefiberarray.Thesingle-modefiberarrayaddsamplitudecontroltothewavefrontcontrolsystemwhenpairedwithapiston/Ap/Alt(PTT)segmenteddeformablemirror(DM).TheLyotstopintheSFAsetupblocksthegapsbetweenthehexagonalsegmentsoftheDM,whichhelpstoeliminatetheintrinsicerrorsfromasegmentedmirror.InpracAce,thissetupwillhelptoremovetheresidualspeckles,whichmaybefurtherremovedbypost-processingincludingPSFsubtracAon.

RadialShearNullingCoronagraphTheRadialShearNullingCoronagraph(RSNC)isbeingexploredasacomplementaryalternaAvetotheexisAngVisibleNullingCoronagraph(VNC)asameansofimprovingthroughputanddiscoveryspacewithopAmalapplicaAontowardfuture10morlargeraperturespacetelescopes.SimilartotheVNC,theRSNCusesdestrucAveinterferenceintherecombinaAonofthebeamsinordertonulloutthelightofthecentralstartoallowfainterexoplanetstobeimaged[4].Thedesignshowninfigure5,mayalsouseaPTTDM.Apairofhybridbeamspli_er-polarizersbiasestheamplitudebetweenthetwoarmsoftheinterferometer.ThetwoopAcalpathshavea10%magnificaAondifferencebetweenthemcausingadifferenceinelectricfieldstrength.Inordertobalancetheamplitude,rotaAngthesecondbeamspli_erallowslessofthelightfromtheDMarmisallowedtopassthrough.ArotaAonaboutthez-axisof19.6°withanerrorof0.042°(0.05%)wasfoundtobalanceouttheamplitudesbetweenthetwoarms.

FutureWorkALICE:•  FurtherresearchintoHD169142toseeifcompanioncandidatesaregravitaAonallybound•  Determinewhaterrorscausedthecompanioncandidatestonotappearinthemiddleofthepredicted0.5arcsec

circles•  Parallax,minorADIreducAonerrors,andorbitalmoAon

•  AdaptreducAonpipelinespecificallyforHD169142SFAandRSNC:•  LabtesAngwithrecentlyconstructedSFAinterferometer.•  ConAnueacquiringRSNCcomponents•  Demonstrate10-8–10-9contrastinlaboratorytesAngwhileillustraAngtheeffectsofoff-axistransmissiononthe

PSFsimilartowhatisshowninFigure6.•  FurtherexplorethecapabiliAesoftheRSNCandSFAinmodelingandexperimenttomoAvateincorporaAonwith

futurespacetelescopesthatwillincludedirectimagingofEarth-likeexoplanetsintheirlistofscienceobjecAves.•  TheRSNCtakesanincrementalsteptowardreachingthetheoreAcalperformancethatwasassumedin

generaAngthesimulatedimageshowninFigure7.

AcknowledgementsIwouldliketothanktheNASAGoddardSpaceFlightCenterandtheUniversiAesSpaceResearchAssociaAonforprovidingmewiththeopportunitytohavethisinternship.ThisresearchwasmadepossiblebysupportfromaSAT/TDEM-13award(PI:B.Hicks).ThisresearchhasmadeuseofdatareprocessedaspartoftheALICEprogram,whichwassupportedbyNASAthroughgrantsHST-AR-12652(PI:R.Soummer),HST-GO-11136(PI:D.Golimowski),HST-GO-13855(PI:E.Choquet),HST-GO-13331(PI:L.Pueyo),andSTScIDirector’sDiscreAonaryResearchfunds,andwasconductedatSTScIwhichisoperatedbyAURAunderNASAcontrastNAS5-26555.

References[1]SoummerR.,PueyoL.,&LarkinJ.2012.TheAstrophysicalJournalLe_ers,755,L28[2]Choquetetal.2014,Proc.SPIE,9143,57[3]HicksB.A.etal.2015.JournalofAstronomicalTelescopes,Instruments,andSystems1(1),019001[4]Lyon,R.G.,Hicks,B.A.,Clampin,M.,&Petrone,P.,III2015,arXiv:1504.05747

IntroducAonDirectlyimagingexoplanetsrequiresacombinaAonofadvancedpost-processingtechniquesaswellascuqngedgeopAcalsystemdesignstolimitnoise,reachasmallerinnerworkingangle,andovercomethecontrastbetweenthestarandtheexoplanet.Currently,theonlyexoplanetsthatcanbedirectlyimagedarebiasedtowardnearbyyoungsystemswithplanetsinlongperiod,largesemi-majoraxisorbits.TheArchivalLegacyInvesAgaAonsofCircumstellarEnvironments(ALICE)programwasstartedtolookatdatafromtheNICMOScoronagraphalongwithnewpost-processingtechniquestouseknowninstrumentpointspreadfuncAons(PSFs)tosubtractthestarlight.Inthefuture,newtechnologiesmustbedevelopedifEarth-likeexoplanetsaretobedirectlyimaged.Contrastorderscloseto10-10canbereachedthroughnewpassivewavefrontcontrolcomponentssuchasaSingle-modeFiberArray(SFA)andopAcalstarlightsuppressionsystemssuchastheRadialShearNullingCoronagraph(RSNC).

Figure3:TwoimagesofHD169142withpredictedlocaAonsforthecandidatesbeingbackgroundobjects(white)orgravitaAonallybound(green).Le[:Imagetakenon06-08-2015Right:Imagetakenon07-04-2015

Figure2:ReducedSPHEREimageshowingcandidatesinpredictedbackgroundlocaAons(white)comparedtothegravitaAonallyboundlocaAons(green)

Figure4:CurrentSFAlayout Figure5:CurrentRSNCopAcaldesign

Figure7:SimulatedviewoftheSolarSystemasobservedfrom10pcwitha10mspacetelescopeusingRSNCtechnology

Figurefrom[4]

Figure6:AslicethroughthesimulatedPSFsofastarandplanetwithmodeledoff-axistransmissionoftheRSNCassuminga4-ringhexagonalapertureand10%imbalanceinmagnificaAon(Figurecredit:BrianHicks)

Figure1:ReducedNICMOSimagesshowingthenewlydiscoveredcompanioncandidatesofHD106797(le[)andHD169142(right)alongwiththegraphsshowingthedetecAonlimitsasafuncAonofdistancefromthestar

Credit:ALICETeamCredit:ALICETeam