Exoplanet Search Techniques:Overview

PHY 688, Lecture 26Mar 27, 2009

Mar 27, 2009 PHY 688, Lecture 26 2

Outline• Course administration

– midterm exam: next Wednesday, April 1– review lecture: Monday, March 30

• come with questions

– final presentations• example topics on course website• select topic during class time on Monday

• Review of previous lecture:– hot Jupiter radii– Rossiter-McLaughlin effect

• Exoplanet search techniques

Mar 27, 2009 PHY 688, Lecture 26 3

Example Presentation Topics• Nearby young brown dwarfs (Josh Schlieder)• Y dwarfs: empirical and theoretical expectations• The 2MASS J0535–0546 brown dwarf eclipsing binary: why is the less massive

component hotter?• The substellar initial mass function: comparison among star forming regions and

implications for the formation of brown dwarfs• Non-equilibrium chemistry in substellar atmospheres• Magnetic activity and rotation in low-mass stars and brown dwarfs• Nemesis: Sun's hypothetical binary companion• The origin of hot Jupiters• The Kozai mechanism and the eccentricities of exoplanet orbits• Searching for exo-earths through gravitational microlensing• Planet formation through core accretion• Planet formation through gravitational disk instability• Planet migration and the architecture of planetary systems• Extremely high contrast imaging of exoplanets: present and future• Dynamical signatures of unseen planets in optically thin circumstellar debris disks

Mar 27, 2009 PHY 688, Lecture 26 4

Outline• Course administration

– midterm exam: next Wednesday, April 1– review lecture: Monday, March 30

• come with questions

– final presentations• example topics on course website• select topic during class time on Monday

• Review of previous lecture– hot Jupiter radii– Rossiter-McLaughlin effect

• Exoplanet search techniques

Mar 27, 2009 PHY 688, Lecture 26 5

Previously in PHY 688…

Mar 27, 2009 PHY 688, Lecture 26 6

Sizes and Structure of Giant Planets:Very Hot Jupiters Are Larger

(Charbonneau et al. 2007)

pM planet

pL planet

Mar 27, 2009 PHY 688, Lecture 26 7

Radii of VeryHot Jupiters

• some large radii cannot beexplained by coreless planetmodels with high-altitudestratospheres:– extra internal power source?

• stratospheric heat trap• tidal heating• damping or orbital eccentricity

and apparent resetting ofplanet age?

– host stars are giga-years old

– preferential evaporation ofneutral helium?

(Fortney et al. 2007)

Mar 27, 2009 PHY 688, Lecture 26 8

Are Some Very Hot Jupiters Younger?

(Fortney et al. 2007)

Mar 27, 2009 PHY 688, Lecture 26 9

Larger Radii through Evaporation ofNeutral Helium

• material evaporated form planetcarries both H and He

• H is ionized, He is not– this depends strongly in strength of

EUV emission from host star– 10,000K temperature is in between

ionization points• strong planetary magnetic field

could limit loss of charged H ionswithout affecting neutral He loss

• decrease of mean molecular weightat constant entropy: larger radius

(Hansen & Barman 2007)

Mar 27, 2009 PHY 688, Lecture 26 10

Rossiter-McLaughlin Effect• first detected in

eclipsing binary stars– as in bottom panel

• effective Doppler shiftof (absorption) linechanges depending onthe part of the host starthat is occulted– stellar line profile may

often be barely resolvedspectroscopically

(Gaudi & Winn 2007)

Mar 27, 2009 PHY 688, Lecture 26 11

RM Effect Geometry:Spin-Orbit Coupling

• seek to measure angle λ between projected stellarrotation axis and planetary orbital axis

(Ohta et al. 2005)

• note: ΩS sin IS here is the same as Vs sin Isand V sin Is in the following slides, andindicates the projected stellar spin rate

Mar 27, 2009 PHY 688, Lecture 26 12

RM Effect Geometry

• shape of deviation from normal radial velocity signaturedepends on λ

(Gaudi & Winn 2007)

Mar 27, 2009 PHY 688, Lecture 26 13

RM Effect Magnitude

• depends on stellar rotation rate and planet-starradius ratio γ = Rp/Rs– photometric measurements of transit give precise and

independent measure of γ

(for γ << 1)

(Gaudi & Winn 2007)

Mar 27, 2009 PHY 688, Lecture 26 14

Observations of RM Effect Due toPlanet Transits

• first observed in HD209458b in 2000

• shown here forTrES-1– only third such

observation– independent Vssin Is

constrain from shapeof stellar spectrallines

(Narita et al. 2007)

Mar 27, 2009 PHY 688, Lecture 26 15

RM Effect in TrES-1: Measuring theProjected Spin-Orbit Angle

(Narita et al. 2007)

Vs sin Is constrained from Dopplerwidth of stellar line profiles Vs sin Is not constrained

Mar 27, 2009 PHY 688, Lecture 26 16

Summary of RM Effect Observationsfor Transiting Planets

• measure projectedspin-orbit angle λ

• infer constraints onactual spin-orbitangle ψ

• ψpeak < 22º at 95%confidence

• broadly consistentwith planetformation in a disk,no major orbitaldisturbance

(Fabrycky & Winn 2009)

Mar 27, 2009 PHY 688, Lecture 26 17

• very sensitive to– V sin Is (projected stellar

rotation velocity)– Rp, Rs– a (orbital semi-major axis)– i (orbital inclination)

• shown is plot of change instellar radial velocity due toRM effect

for various parameters p

• useful for– studying planet atmospheres– detecting/confirming wide

planets

The RM Effect: Other Applications

(Ohta et al. 2005)

Mar 27, 2009 PHY 688, Lecture 26 18

Using the RM Effect to ProbeAtmospheric Composition

• employ the strong Rp/Rs dependence

(Dreizler et al. 2009)

Mar 27, 2009 PHY 688, Lecture 26 19

Detecting Exo-Earth’s through theRM Effect

(Gaudi & Winn 2007)

Earth’s r.v. andRM signature

• note: i and I are the same variablein the top equation above

(latter equality true for m << M, e = 0)

Mar 27, 2009 PHY 688, Lecture 26 20

Outline• Course administration

– midterm exam: next Wednesday, April 1– review lecture: Monday, March 30

• come with questions

– final presentations• example topics on course website• select topic during class time on Monday

• Review of previous lecture:– hot Jupiter radii– Rossiter-McLaughlin effect

• Exoplanet search techniques

Mar 27, 2009 PHY 688, Lecture 26 21

From Lecture 2: DetectionTechniques for Substellar Objects

• precision radial velocity monitoring– periodic Doppler shift of host star

spectrum due to planet’sgravitational pull

• resolved imaging of binary systems– seeing-limited, speckle

interferometry, adaptive optics• unresolved photometry of hot stars

– e.g., cool infrared excess in anotherwise much hotter white dwarf

• large-area sky surveys– extremely red objects

• precision radial velocity monitoring• pulsar timing

– apparent periodicity in pulsarrotation period due to planet’sgravitational pull

• transit photometry– ~1% dimming of star due to planet

passing in front• microlensing

– gravitational lensing of light frombackground stars

• resolved imaging!– extremely high-contrast adaptive

optics

brown dwarfs exoplanets

Mar 27, 2009 PHY 688, Lecture 26 22

Planet Detection Methods(statistics as of Oct 2007)

(Perryman 2000)

Mar 27, 2009 PHY 688, Lecture 26 23

Planet Detection History

318 radial velocity58 transits8 microlensing7 pulsar timing4 (11) imaging

Mar 27, 2009 PHY 688, Lecture 26 24

Planet Detection:Direct Imaging

• 2MASS 1207–3932 B~ 5 MJup

• primary is a young(~10 Myr) browndwarf

• discovered withadaptive optics (AO)on the 8 m Very LargeTelescope (VLT)

(Chauvin et al. 2004)

Mar 27, 2009 PHY 688, Lecture 26 25

Planet Detection: Direct Imaging

• Fomalhaut b~1–3 MJup

• discoveredwith theHubble SpaceTelescope(HST)

(Kalas et al. 2005)

Mar 27, 2009 PHY 688, Lecture 26 26

Planet Detection: Direct Imaging• HR 8799 bcd: ~10–15 MJup

• discovered with adaptive optics on the 10 m Keck telescope

b c

d

(Marois et al. 2008)

Mar 27, 2009 PHY 688, Lecture 26 27

Challenge of Direct Imaging:Star-Planet Contrast

• In the visible–near-IR– FSun / FEarth ~ 109

– FSun / FJup ~ 108

– challenging wavefrontcontrol

– small PSF– can observe from the

ground• In mid-IR

– FSun / FEarth ~ 106

– FSun / FJup ~ 104

– easier wavefront control– >10 × larger PSF– need to observe from

space

Mar 27, 2009 PHY 688, Lecture 26 28

Challenge of Direct Imaging:Star-Planet Contrast

r = 1″

Keck AO speckles at 2.2 µmKeck AO speckles at 2.2 µm

exoplanetsexoplanets

(Kalas 2005)

• high angular resolution,high-contrast imagingsuffers from wavefrontaberrations or order ~ λ

• aberrations manifested as“speckles” of size ~ λ/D

• speckles pose as“fake”planets

2M 1207 B (~5 MJup)

HR 8799 b,c,d (~10–15 MJup)

bcd

Mar 27, 2009 PHY 688, Lecture 26 29

Planet Detection: Imaging• state of the art: contrast of 9 mag at 0.5", 11 mag at 1" in the near-IR• benefits: can perform atmospheric spectroscopy• limitations:

– hot (young), well-separated (>0.5") planets– no mass, radius information

• false positives: telescope speckles, distant background stars