TransitSpectroscopy

JacobBean

UniversityofChicago

Somerecentreviews:

•  “ExoplanetaryAtmospheres—Chemistry,Forma6onCondi6ons,andHabitability”Madhusudhan+2016

•  “Observa6onsofExoplanetAtmospheres”Crossfield2015

SpectralRetrievals

Keyreferences:•  Madhusudhan&Seager2009

•  Benneke&Seager2012,2013ßforsuper-Earths

•  Benneke2015,arXiv:1504.07655•  Lineetal.2013ac,2014a,2016•  Lineetal.2014b,2015ßforbrowndwarfs

•  Leeetal.2013;Todorvetal.2016ßfordirectlyimagedplanets

•  Barstowetal.2013ab

WhyHighPrecisionSpectroscopy?

Effectofthepriors

Line+2013a

“ToofewdatapointsinpursuitoftoomanyquanVVes”

Burrows2014b

WhyHighPrecisionSpectroscopy?

Theunknownunknowns

Saturnobservedasatransi6ngexoplanetwithCassini

Dalba+2015

?

WhyHighPrecisionSpectroscopy?

Imean,trulyhighprecisiondata

Grillmair+2008

10eclipses2eclipses

Grillmair+2007

FundamentalThemesforExoplanet

AtmosphereCharacterizaKon

Determiningthermalstructures,energybudgets,anddynamicstounderstand

planetaryphysics.

MeasuringcomposiVonstotraceplanetformaVonand

evoluVon.

ConnectedquesVonsmoVvatesholisVcstudies.

ComparaKveplanetologyinthe

SolarSystem

Jupiter Saturn

Uranus Neptune

Terrestrialplanets

ComparaKveplanetology:JupiterandSaturn

Bandedappearancesduetodynamicsofatmosphere:internalheat+fastrotaVon.SourceofcolorsislikelycomplexmoleculesformedoncloudparVclesduetophotochemistry,butexactnatureisuncertain.

ThinnercloudsonJupiterexplainswhyithasstrongercontrastbetweenzonesandbelts.

ComparaKveplanetology:JupiterandSaturn

Uranus Neptune

Nearlyfeatureless,colorduetoreflectanceofmethane.

Faintbandedstructure(slightlyfasterrotaVonandinternalheat),wispyclouds,andGreatDarkSpot.

ComparaKveplanetology:UranusandNeptune

SlightdifferencesbetweenUranusandNeptuneduetointernalheat,distancefromtheSun,andsurfacegravity.

ComparaKveplanetology:UranusandNeptune

AtmosphericComposiKon

•  Giantplanetatmospheresare“primaryatmospheres”.•  JupiterandSaturnhaveatmosphericelementalabundancesverysimilar

totheSun(dominatedbyH/He,withtraceheavierelements).

•  TheatmospheresofUranusandNeptunearealsosimilarincomposiVonastheSun,butwithaslightlygreaterenhancementofmetals(dominatedbyH/He,withsignificantCH4andtraceheavierelements).

•  Theabundancesinallfourplanets’atmospheresarestronglyaffectedby

condensaVon:§  Waterinalltheplanetsisnotobservablebecauseithassehledout

oftheupperatmosphere.§  Cloudsdominatetheappearancesoftheplanets.§  HeliumisdeficientinJupiter’sandSaturn’supperatmospheres,

likelybecauseitisrainingout.

•  Non-equilibriumeffects(photochemistry,verVcalmixing)aresignificant.

Atreya+,arXiv:1606.04510

TerrestrialPlanetAtmospheres

“Secondaryatmospheres”stronglyinfluencedbymassloss,geophysicalandbiologicalprocesses,etc.

HowToObserveExoplanetAtmospheres

•  Transits/OccultaVons•  DirectImaging

TransitsandOccultaKons

Transits:EmissionSpectroscopy

Ifreflectedlightdominates:Fp/Fs=AG(Rp/a)2(phasefuncVon=1atsecondaryeclipse)Ifthermalemissiondominates:Fp/Fs=(Rp/RS)2[Bλ(TP)/Bλ(Ts)]

Whatismeasuredistheplanet-to-starfluxraVo:

ThethermalemissionsignalintheinfraredforahotJupiteraroundaSun-likestar(Teq=1600K)isonorderof10-3.

Transits:EmissionSpectroscopy

TheoreVcalpredicVonsforhighly-irradiatedplanets

Fortneyetal.2008,ApJ,678,1419

Transits:EmissionSpectroscopy

Ground-based,short-wavelength,faintstarWASP-19b

Beanetal.2013,ApJ,771,108

Transits:EmissionSpectroscopy

Space-based,longer-wavelength(3.6and4.5μm),brightstar

SpitzerSpaceTelescope

HD189733b

Knutsonetal.2012,ApJ,754,22PrevioussensiVvitytolongerwavelengths,butnolonger.

Transits:EmissionSpectroscopy

Beanetal.2013,ApJ,771,108

TransitsandOccultaKons

Transits:TransmissionSpectroscopy

Thekeypointisthattheedgeoftheplanetis‘fuzzy’ratherthansharpduetotheatmosphere.Therefore,thetransitdepth(apparentsizeoftheplanet)dependsonthewavelengthoflight.

Transits:TransmissionSpectroscopy

TheoreVcalpredicVons

Fortneyetal.2010,ApJ,709,1396

T=2500K2000K1500K1000K500K

Transits:TransmissionSpectroscopy

Ground-baseddata

GJ1214b

Bean+2010c

Transits:TransmissionSpectroscopy

Scaleheight:

Strengthoffeaturesinatransmissionspectrumdependonthescaleheightoftheatmosphereandthestrengthoftheabsorber.

Strengthoffeatures:

WheretheproporVonalityfactordependsonthestrengthofabsorpVon(e.g.,afactorofafew)andtheresoluVon

Transits:TransmissionSpectroscopy

Moreprecisely:

Huitsonetal.2012,MNRAS,422,2477BasedonLecavelierdesEtangsetal.2008,A&AL,481,83

abundanceoftheabsorbingchemicalspecies

Transits:TransmissionSpectroscopy

Realdata TheoreVcalmodels

HD209458b

Charbonneauetal.2002,ApJ,568,377

Transits:TransmissionSpectroscopy

CondensaVon

Fortneyetal.2008,ApJ,683,1104Fortney2005,MNRAS,364,649

TransitsandOccultaKons

Transits:Phase-ResolvedEmission

Spectroscopy

Realdata

HD189733b

Knutsonetal.2007,Nature,447,183

Transits:Phase-ResolvedEmission

Spectroscopy

Transits:Phase-ResolvedEmission

Spectroscopy

Showmanetal.2009,ApJ,699,564

TheoreVcalpredicVonsusingaGCM

Challenges

•  CollecVngenoughphotons•  Aperture(slit)losses•  PoinVngvariaVons+inter-andintra-pixelsensiVvityvariaVons

•  Detectorpersistence•  TellurictransparencyvariaVonsandcontaminaVon

•  Limbdarkening

•  StellaracVvity•  Mysteryeffects

AstronautAndrewFeustelinstallstheWideField

Camera3(May14,2009)

Usinganinstrumentdesignedforfaintgalaxiestolookatbright,nearbystars

spectraldirecVon

spaV

aldire

cVon

HST+WFC3spaValscan

Kreidberg+2014a

Berta+2012

HST+WFC3:staringmode

Challenges

•  CollecVngenoughphotons•  Aperture(slit)losses•  PoinVngvariaVons+inter-andintra-pixelsensiVvityvariaVons

•  Detectorpersistence•  TellurictransparencyvariaVonsandcontaminaVon

•  Limbdarkening

•  StellaracVvity•  Mysteryeffects

WhiteLightCaseStudy#1:HAT-P-1b

howwidedotheslitshavetobe?

HAT-P-1

IdenVcalcompanion11�

6�slit

WhiteLightCaseStudy#1:HAT-P-1b

howwidedotheslitshavetobe?

CalarAlto3.5m+TWIN

badguiding differenValslitlosses

WhiteLightCaseStudy#1:HAT-P-1b

howwidedotheslitshavetobe?

CalarAlto3.5m+MOSCA

12�slit rms=330ppm!

(includesspaValposiVonde-correlaVon)

WhiteLightCaseStudy#2:GJ1214b

mul6-objectspectrograph–VLT+FORS

5.5� 12�slitlets

spectrum

WhiteLightCaseStudy#2:GJ1214b

mul6-objectspectrograph–VLT+FORS

Bean+2010

Challenges

•  CollecVngenoughphotons•  Aperture(slit)losses•  PoinVngvariaVons+inter-andintra-pixelsensiVvityvariaVons

•  Detectorpersistence•  TellurictransparencyvariaVonsandcontaminaVon

•  Limbdarkening

•  StellaracVvity•  Mysteryeffects

Stevenson+2012

Spitzer+IRAC

Challenges

•  CollecVngenoughphotons•  Aperture(slit)losses•  PoinVngvariaVons+inter-andintra-pixelsensiVvityvariaVons

•  Detectorpersistence•  TellurictransparencyvariaVonsandcontaminaVon

•  Limbdarkening

•  StellaracVvity•  Mysteryeffects

HST+WFC3

Kreidberg+2014a

Challenges

•  CollecVngenoughphotons•  Aperture(slit)losses•  PoinVngvariaVons+inter-andintra-pixelsensiVvityvariaVons

•  Detectorpersistence•  TellurictransparencyvariaVonsandcontaminaVon

•  Limbdarkening

•  StellaracVvity•  Mysteryeffects

VLT+CRIRES

Brogi+2012

Challenges

•  CollecVngenoughphotons•  Aperture(slit)losses•  PoinVngvariaVons+inter-andintra-pixelsensiVvityvariaVons

•  Detectorpersistence•  TellurictransparencyvariaVonsandcontaminaVon

•  Limbdarkening

•  StellaracVvity•  Mysteryeffects

GJ1214bwithHST+WFC3

Kreidberg+2014a

Challenges

•  CollecVngenoughphotons•  Aperture(slit)losses•  PoinVngvariaVons+inter-andintra-pixelsensiVvityvariaVons

•  Detectorpersistence•  TellurictransparencyvariaVonsandcontaminaVon

•  Limbdarkening

•  StellaracVvity•  Mysteryeffects

StellaracVvityforHD189733b?

McCullough+2014

Challenges

•  CollecVngenoughphotons•  Aperture(slit)losses•  PoinVngvariaVons+inter-andintra-pixelsensiVvityvariaVons

•  Detectorpersistence•  TellurictransparencyvariaVonsandcontaminaVon

•  Limbdarkening

•  StellaracVvity•  Mysteryeffects

Gemini+GMOSStevenson+2014a

HST+WFC3

Stevenson+2014b

MIRI

5μm

ThepotenValofJWSTfortransitspectroscopy

MIRI

5μm

MIRI

5μm

Transmissionspectroscopy

MIRI

5μm

TransmissionspectroscopyFullorbitphasecurve(withtwosecondaryeclipses)

MIRI

5μm

TransmissionspectroscopyFullorbitphasecurve(withtwosecondaryeclipses)Secondaryeclipseofabrightstar

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