1 2 9–3 9–4 ) city measurements separate images of gravitational lensing motion of : Direct Imaging Detection Methods of ” of telescope (angular distance between star and planet) search for evidence for... with telescope imaging ” (relative intensity of star and planet) ways to detect extrasolar ...direct ...gravitational interaction with star in ...influence of planet on light from behind planet ( ALEX ...gravitational interaction with star in ALEX O AN O AN C D C D I R I R R R Requires two ingredients:

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D D A A C C A A 1. “ 2. “ = Direct Method: In order to make an image of an extrasolar planet, need to Possible For time reasons: will look atonly... direct imaging and radial velo Detection Methods star and planet Detection Methods Indirect Methods: 1 9–1 9–2 . extrasolar planets Introduction Extrasolar Planets Is our normal?

ALEX ALEX O AN O AN C D C D I R I R R R Are there planets around other ?

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D D A A C C A A can then compare solar system with other systems. To answer these questions, we need to detect So far: have looked at planets around our Physics question: = Extrasolar Planets 7 8 9–6 9–7 . ⊙ L ′′ 10 03 . − 0 r , 10 = m me , × Star ”) 11 m 6 a deg 17 10 2 ∼ 6 − − 10 × W 5 10 × . r d 17 1 5 × . ∼ 10 9 = 9 W. 51Wm we need to be able to detect θ × . = 17 = ∼ 5 . 10 1 AU 2 P rad ⇒ × small angle approximation 7 = d ∼ = ⇒ − ; “ 2 100 Ly r . = X 8 θ . . . 10 ∼ r d L + = km d × 3 1 billion times weaker than that of the Sun. = θ 8 ) ∼ X 3 θ , 57 / 10 . 1 1 total × tan +( P = 8 θ 2 . r d Direct Imaging: Contrast, V 7 m ∼ θ 16 = = θ tan 10 Direct Imaging: Angular Separation, I × 2 AU Earth . 3600 deg). 6 5 / . 1 1 ⇒ = = = = r : Taylor series: 2 X θ

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intensity contrasts of better than 1:1billion For typical planets around solar type stars, Not doable now, but not unrealistic to achieve in your lifeti

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D D A A C C A A Of this, about 30% is reflected, i.e., Typical distances to nearby stars: Plugging in typical numbers: Jupiter: distance: Total power received by Jupiter: projectedA solar facing are = = Detection Methods How close on sky are images of Sun and planet? (for small typical distances in planetary system: (1 Detection Methods = 5 6 9–5 9–6 . (area ⊙ t of the r L 2 ”): 10 L πr as well! − 4 flux L (“ 10 = ⊙ r 1 L − ∼ F s 2 − =: W 16 ) equals W 2 W. 10 26 πr 17 or ergcm × at distance 4 10 2 − 2 2 10 . = × 5 × A Energy falling per second on area1 m of Energy received per second on whole area of sphere of radius ll rather weak. . . 90 = . 74 ”). 3 ⇒ ⇒ .  1 = This power is emitted isotropically intodirections. all = units: Wm L = = L km  6 , 10 total P 2 × of Sun m solar constant Direct Imaging: Contrast, III Direct Imaging: Contrast, IV (“ 14 150 2 r 10 − = × Luminosity 26 1 AU . 1 Star = = r 1380Wm 2  ∼

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D D A A C C A A Of this, about 30% is reflected, i.e., = Plugging in typical numbers: Estimate intensity contrast between star and planet: Solar system: Total power received by Earth: projectedA solar facing area Detection Methods Earth: distance: in infrared, luminosity contrast is only 10 million, but sti Detection Methods = × 2 ∼ enough. h imaging nciple doable with 7pc. ± Using adaptive optics, it is possible to obtain diffraction limited resolution in the near infrared. Contrast is still a problem, however, for one very dim star (a “brown dwarfs”) a planetary companion was detected in early 2005 with the VLT and confirmed in 2006 with HST. Distance between star and planet: Neptune distance, distance to system 59 ...while planets around normalmethods, stars direct have imaging yet of to the be regionHubble found close Space wit to Telescope, but a angular star resolution is not in yet pri good 12 9–8 (8.8) : 2 missions in escopes (TPF-I, ible from olar-type stars is : ”) D seeing (“ One possible configuration of ESA’s Darwin mission: several free-flying mirror spacecraft plus one spacecraft serving as communications hub. ′′ ′′ 1 cm Terrestrial Planet Finder 5 12 . 0 D/ and ∼ , so doable = BUT α 4 m = D of telescope with diameter , need ′′ 3m telescopes, launch planned for 2015 Direct Imaging: Angular Separation, V 03 . & : 3 resolving power Space Interferometry Mission Darwin ALEX O AN C D I R R to resolve 0 E I

Currently, direct detection of extrasolar planetsnot around doable s from ground, although it is technologically feas space. D A N I

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D A C A Optics: = NASA: Detection Methods Earth atmosphere limits resolution to the next decade(?): 4–6m telescopew/ESA) (TPF-C); multiple 3–4m tel ESA: 19 9–15 , which is 8 − 10 Lines emitted × : 4 = line from in α λ/λ H ∆ Fraunhofer Lines c v ⇒ = Doppler-effect = : Light, such as all waves, suffers 1 − from moving star are Doppler shifted: Using modern spectrographs, position of absorption lines can be measured with very high precision. Example: solar spectrum. but from emitted λ − 657.0 13ms emitted λ = v observed λ Radial Velocity Measurements N.A. Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF Wavelength (nm)   Absorption line spectrum of the Sun: Solar Atlas (after Delbouille et al.,1972, 1981)

ALEX O AN C D I R R Can use line shifts to detect extrasolar planets!

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D 10000 A C A only doable by using many tricks. = ...but need good spectrograph: Detection Methods , : 16 17 s 8 P 9–12 9–13 10 × 2 r 76 · . planet 3 2 1 = 2 m m r and · with 2 center of 9 yr π . m P 2 11 Star = = = 1 . 1 J r 1 P P πr . m 2 m, 11 = 10 1 1 v − × 8 . 7 . 8kmh = 1 . indirect methods 0 Two-body problem: move around common velocity of star due to action of planet is For circular orbits and − ∼ 2 AU . 1 use 5 − = ⇒ 2 = r 2 spectroscopic methods m 10cms kg, = 1 27 1 − v 10 × Radial Velocity Measurements Radial Velocity Measurements 2 50kmh = ∼ 2 1 m − CM kg, 1 2 30 1ms r r . 10 Sun vs. Jupiter: Sun vs. Earth gives 13 × = ALEX ALEX O AN 2 O AN C D C D I 1 I R R R R I I

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D D A A C C A A Example: Example: Detection Methods Measure motion of stars using Detection Methods m If we cannot see planet directly = 3 4 9–18 9–19 X M>M Andromedae.  M υ 318 = X Many (most!) Planets found have M 20 not mean that they do not exist, just that we around Gliese 876 400  M 5 . ] 300 Earth 15 Results, III 200 ] Results: Mass, I Mass [M larger velocity amplitude 100 Jupiter ⇒ = 10 0

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D D A A C C A A cannot detect them yet. Smallest mass found so far: 7 So, the fact that we have not seen any Earth-like planets does = G. Marcy/UC Lick Results Selection effect: Results 1 2 9–16 9–17 : rcling of telescope Changing radial . lots very good 1 − velocity of HD 130322 results in discovery of Jupiter-mass planet (Udry et al., 2000). Here: velocity amplitude: 115ms Example: Radial velocity = velocity along ourof line sight. Doppler Detection Method spectrograph changes in velocity of stars due to motion of star around CM time 1. get access to 3. measure for , to determine 2. get access to How to hunt extrasolar planets using the Results, I Results, II unseen planet

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As of 2006 November 28, 195172 extrasolar stars. planets were known, ci

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D D A A C C A A G. Marcy Results Results 8 9 9–23 9–24 short no life! ... ⇒ = bserving runs the previous slide: Most planets found in short orbits! Many planets are in eccentric orbits! 1000 100 1.0 disturbances of Earth’s orbit 80 800 always seem to hold! 60 not strong 0.8 40 Results: Period ⇒ = 600 Results: Eccentricity 20 Orbital period [days] 0.6 0

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D D A A C C A A Statistics is direct consequence of the selection effect of Results different from solar system! Might be selection effect due toJupiter our in existence: eccentric orbit in our solar system So, in some sense Copernican principle does Results period planets are detectable during typical durations of o 6 9–21 )! planet is 1 − kgs 7 (HST spectroscopy: Most planets found are close to companion star! 6 mass loss is 10 ESA Jupiter-scale planets close to stars: “hot Jupiters” e.g., HD 209458b, only 7 Million km from star: evaporating 2.0 1.5 1.0 4 short period 0.5 Semimajor Axis [AU] ⇒ Results: Semimajor Axis, I = 0.0

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D A C A Selection effect: Results = ESA D.M.Hardy / PPARC But not all is bleak – HD 70642 (d = 90 ly): discovered by Hugh Jones (Liverpool John Moores University): Jupiter mass planet at 3AU from solar-like star in circular orbit =⇒ stable Earths are possible.