the role of precision spectroscopy in the search for earth 2sampa/ps2017/talks/bean1.pdf · the...

TheRoleofPrecisionSpectroscopyintheSearchforEarth2.0

JacobBeanUniversityofChicago

radialvelocity

transit

directimaging

microlensing

N≈5000

Knownexoplanets

Theroleofprecisionspectroscopy…


Radialvelocityplanet

detec?on



detec?on

Exoplanetatmospheric

characteriza?on



detec?on

Exoplanetatmosphere

studies

Hoststar

characteriza?on



detec?on

RadialVelocityTechnique

Whatcanyoudetermine?

Asmallplanetinthehabitable

zonearoundournearest

neighbor,ProximaCentauri

“Cross-DispersedEchelle”Spectrogrpah

LimitaGonstoinstrumentstability

•  Changesinthespectrographresponse.(e.g.,mechanicalmoGonofthespectrographordetector,changesintherefracGveindexofairinsidethespectrograph)

•  ChangesinthelightinjecGon.

Strategiesforinstrumentstability

•  Stabilizetheinstrumentwithextensiveengineering.•  Calibratefor(smallorlarge)changes.

Verystabilizedinstruments:[email protected]/Chile

Spectrographonarigid

bench,whichishousedina

vacuumtank.




vacuumtank.

Thetankitselfishousedin

aclimatecontrolledroom

thatisneveropened.

•  Pressurecontrolledto10-3mbar

•  Op?calbenchcontrolledto1mK




vacuumtank.



thatisneveropened.

Lightiscoupledfromthe

telescopewithfiberop?cs

that“scramble”thelight.




vacuumtank.



thatisneveropened.

Lightiscoupledfromthe

telescopewithfiberop?cs

that“scramble”thelight.

Asecondfiberfeeda

simultaneouscalibra?on

source.


Cross-Correla?onTechnique

observedspectrum

templatespectrum

CCF

radialvelocity

Originalreference:

Tonry&Davis1979,AJ,84,10

Strategiesforinstrumentstability

•  Stabilizetheinstrumentwithextensiveengineering.•  Calibratefor(smallorlarge)changes.

Gascelltechnique

RadialVelocityTechnique

RadialVelocityTechniqueiodinelines

Gascelltechnique:Itisali\lemorecomplicated

instrumentalprofile

Butleretal.1996,PASP,108,500

Calibratedinstruments:HIRES@10mKecktelescopeinHawaii

Spectrographnot

par?cularlystabilized.

KnownplanetsfromRV

StellarLimita?onstoMeasuringRVs(Jiber)

Jiberiscausedbynon

uniformityofthestellar

diskasafunc?onof?me.

Examples:

•  Acous?cpressuremodes(P-modes)

•  Granula?on

•  Spots,plage,faculae

RVplanetsasafuncGonofdate

alphaCenBb

(notreal)

51Pegb

HD114762b

ProximaCentaurib

(probablyreal!)

TheAlphaandProximaCentauriSystem

•  AlphaandProximaCentaurisystemisatriplestar

systemwithtwoSun-likestars(AandB)andalow-mass

star(Proxima,M=0.1Msun).

•  AandBorbiteachotherin80years.Periastrondistance

is11AU.

•  Proximaismuchfurtherawayandhasaverylongperiod

(P>100,000years).

•  Thisisthecloseststarsystemtous(d=4.4ly).

AsmallplanetaroundalphaCentauriB


alphaCentauridoesn’tevenhaveplanets.WEAK!Ofcoursewehave

thebestplanetsinthesolarsystem–THEBEST!


Dumusqueetal.2012,Nature,491,207

AsmallplanetaroundalphaCentauriB– Probablynot!

Rajpaul+(2016)

Realdata Simulateddatawithnoplanet

AsmallplanetaroundProximaCentauri


FINALLYanothersolarsystemdelivers.JustlikeObamacare,adaylate

andadollarshortthough.Besttacobowls?llatTrumpTower

Sevenplanetsaroundasinglestar?

Lovisetal.2011,A&A,528,112

HD10180

Sevenplanetsaroundasinglestar?

Lovisetal.2011,A&A,528,112

Newradialvelocityspectrographs

Seereviews: Plavchan+(2015,arXiv:1503.01770)

Fischer+(2016,arXiv:1602.07939)

Wright(2017,arXiv:1707.07983)



detec?on


Exoplanetatmospheric

characteriza?on

Textbookchapter:Winn(arXiv:1001:2010)

Thethingsthatyoucandirectlymeasure:

•  Transitdura?on

•  Ingress/egress?me

•  Transitdepth

•  Mid-transit?me

•  Timebetweensuccessivetransits

Thingsthatyoucanderivefromtheseobservables:

•  Orbitalperiod

•  Orbitalephemerides

•  Ra?oofthesizeoftheplanettothesizeofthehoststar(Rp/Rs)

•  Impactparameter,b=acosi/Rsfore=0

ThingsthatyoucanusethesevaluestodeterminewithKandefromRV,and

es?mateofMs:

•  Ra?oofthesizeofthesemi-majoraxistothesizeofthehoststar(a/Rs)

•  Orbitalinclina?on

•  Planetmass•  afortheorbitusingNewton’sversionofKepler’sthirdlaw

•  Radiusofthestar

•  Radiusoftheplanet•  Densityofthestar

•  Surfacegravityoftheplanet

Twoways:

•  Lookforthetransitswithnopriorknowledge

•  Lookfortransitsofplanetsfoundwiththeradialvelocitymethod

FindingtransiGngplanets

Recallthetransitprobability:

ForaHotJupiter,p≈10%

Buttheseplanetshaveafrequency,η≈1%

Thereforeonorderofathousandstarshavetobesearchedfor

findjustasingleplanetthisway.

TransitSearches:thebadnews

Recallthetransitdura?on:

ForaHotJupiteraroundaSun-likestar,Ttot≈3hours

Whichis≈5%oftheorbitalperiod(e.g.,3days).

So,onehastosearchmanythousandsofstarscon?nuouslyfor

daysata?me.

TransitSearches:thebadnews

Recallthetransitdepth:δ=(Rp/Rs)2(neglec?nglimbdarkening)

ForaHotJupiteraroundaSun-likestar,δ≈1%

Sayyouwanttodetectthissignalat10σconfidence…

S/N=sqrt(Nphotons)

HowmanyphotonsdoyouneedtocollecttogetS/N=10?

Ameasly1x106photons!

Thiscanbedonewithamateurequipment!

TransitSearches:somegoodnews

Rememberthetransitdepth:(Rp/Rs)2!!!

Jupiter:1.5%transitdepth

HD209458b–fromtheground

Neptune:0.5%transitdepth

GJ436b–fromtheground,butan

Mdwarfhost

Super-Earth:0.05%transitdepth

55Cnce–fromspace

TransitSearches:Gmeline

HD209458b

TransitSearches:whythedrought?

1.MorenoisethanexpectedfromtheEarth’satmosphere

Scin?lla?on:

Thevaria?onsinintensitycomponentof

atmospheric‘seeing’.


2.Ahighrateofastrophysicsfalseposi?ves


3.HotJupitersarenotverycommon

Frequencyisaliblelessthan1%

TheKeplerMission

Acustom-built,0.95mdiameterspace

telescopededicatedtofindingtransi?ng

planets

Cost:$600M

Launchedin2009

Observingstrategyistostareatthesame

fieldfor3+years

1000softransi?ngplanetsfound

Recentlypassedthe2000papermark

SpacecrayfailureinMay2013

Kepler-62:afiveplanetsystemwithtwosuper-Earthsinthehabitablezone

AnnouncedApril19,2013

KepleràK2

SevenEarth-sizeplanetsaround

thebrowndwarfTRAPPIST-1

Gillon+2016,2017

TESS:TransiGngExoplanetSurveySatellite

Anewspacetelescopeto

findsmalltransi?ngplanets

aroundbrightstars–these

aretheplanetsthatwe

couldstudyinmoredetail.

NASAmission

$200Mcost

4x10cmlenses

Scheduledforlaunchin2018

Mostlyplanetsinshort-

periodorbits,butmayfind

habitable-zoneplanets

aroundsmallstars

TheJamesWebbSpaceTelescope

TheJWSTistheintellectual

successortoHubble.

Itwillhavea6.5mmirrorthatis

op?mizedforinfrared

observa?ons.

Itisscheduledforlaunchin

2018.

Thees?matedcostofthe

projectis$8B.



detec?on

Exoplanetatmosphere

studies


Hoststar

characteriza?on

Howard2013,Science,340,572

Bothradialveloci?es

andtransitsdependon

stellarcharacteriza?on

toderivetheabsolute

planetproper?es

Fulton+2017

Theimportanceofprecisestellar

characteriza?on

Valen?&Fischer2005

Hoststarsareafossilrecordofplanetforma?on

Melendez+(2009)

Bedell+2017

InterpretTTVmasseswithcau?on:

Re-evalua?ngtheKepler-11system

High-precisionspectroscopy(S/N=250)

withdifferen?alequivalentwidthtechnique

Low-precisionspectroscopy(S/N=30)with

spectralfi|ng

[M/H]=+0.06isochrones

Sun


Re-evalua?ngtheKepler-11system

Bedell+2017Planetdensi?eschangeby20–95%!


CanwetrusttheTRAPPIST-1masses?

Wang+2016

Challengeslookingforward•  RadialvelocityplanetdetecGon:

•  Howdowedisentanglestellarjiberandinstrumentalnoisefromthe

signalsofEarthtwins?

•  Howdowebestusethenextgenera?onoflargetelescopes?•  HowdowemeasurethemassesofalargesampleofTESSplanets?

•  HoststarcharacterizaGon:•  Canweconnectstellarabundancestoplanetforma?onbeyondthe

giantplanet–metallicitycorrela?on?

•  Howdoweaccuratelycharacterizelargenumbersofexoplanethost

starsintheTESSera?

•  Transitspectroscopy:•  HowmuchofJWST’spoten?alpowerwillwebeabletousefortransit

spectroscopy?

•  Howdowemovebeyondone-offstudiestothesta?s?cal

inves?ga?onofexoplanetatmospheres?

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