the role of precision spectroscopy in the search for earth 2sampa/ps2017/talks/bean1.pdf · the...
TRANSCRIPT
Theroleofprecisionspectroscopy…
Radialvelocityplanet
detec?on
Exoplanetatmosphere
studies
Hoststar
characteriza?on
LimitaGonstoinstrumentstability
• Changesinthespectrographresponse.(e.g.,mechanicalmoGonofthespectrographordetector,changesintherefracGveindexofairinsidethespectrograph)
• ChangesinthelightinjecGon.
Strategiesforinstrumentstability
• Stabilizetheinstrumentwithextensiveengineering.• Calibratefor(smallorlarge)changes.
Verystabilizedinstruments:[email protected]/Chile
Spectrographonarigid
bench,whichishousedina
vacuumtank.
Verystabilizedinstruments:[email protected]/Chile
Spectrographonarigid
bench,whichishousedina
vacuumtank.
Thetankitselfishousedin
aclimatecontrolledroom
thatisneveropened.
• Pressurecontrolledto10-3mbar
• Op?calbenchcontrolledto1mK
Verystabilizedinstruments:[email protected]/Chile
Spectrographonarigid
bench,whichishousedina
vacuumtank.
Thetankitselfishousedin
aclimatecontrolledroom
thatisneveropened.
Lightiscoupledfromthe
telescopewithfiberop?cs
that“scramble”thelight.
Verystabilizedinstruments:[email protected]/Chile
Spectrographonarigid
bench,whichishousedina
vacuumtank.
Thetankitselfishousedin
aclimatecontrolledroom
thatisneveropened.
Lightiscoupledfromthe
telescopewithfiberop?cs
that“scramble”thelight.
Asecondfiberfeeda
simultaneouscalibra?on
source.
Verystabilizedinstruments:[email protected]/Chile
Cross-Correla?onTechnique
observedspectrum
templatespectrum
CCF
radialvelocity
Originalreference:
Tonry&Davis1979,AJ,84,10
Strategiesforinstrumentstability
• Stabilizetheinstrumentwithextensiveengineering.• Calibratefor(smallorlarge)changes.
StellarLimita?onstoMeasuringRVs(Jiber)
Jiberiscausedbynon
uniformityofthestellar
diskasafunc?onof?me.
Examples:
• Acous?cpressuremodes(P-modes)
• Granula?on
• Spots,plage,faculae
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!
AsmallplanetaroundProximaCentauri
FINALLYanothersolarsystemdelivers.JustlikeObamacare,adaylate
andadollarshortthough.Besttacobowls?llatTrumpTower
Newradialvelocityspectrographs
Seereviews: Plavchan+(2015,arXiv:1503.01770)
Fischer+(2016,arXiv:1602.07939)
Wright(2017,arXiv:1707.07983)
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:whythedrought?
1.MorenoisethanexpectedfromtheEarth’satmosphere
Scin?lla?on:
Thevaria?onsinintensitycomponentof
atmospheric‘seeing’.
TheKeplerMission
Acustom-built,0.95mdiameterspace
telescopededicatedtofindingtransi?ng
planets
Cost:$600M
Launchedin2009
Observingstrategyistostareatthesame
fieldfor3+years
1000softransi?ngplanetsfound
Recentlypassedthe2000papermark
SpacecrayfailureinMay2013
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.
Howard2013,Science,340,572
Bothradialveloci?es
andtransitsdependon
stellarcharacteriza?on
toderivetheabsolute
planetproper?es
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
InterpretTTVmasseswithcau?on:
Re-evalua?ngtheKepler-11system
Bedell+2017Planetdensi?eschangeby20–95%!
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?