Properties, Pitfalls, Payoffs, and Promises

B. Scott Gaudi Harvard-Smithsonian Center for Astrophysics Outline:

„ Star and Planet Formation „ Migrating Planets „ Basic Properties of Planet Transits „ Challenges in Transit Surveys „ The Menagerie of Transit Surveys „ Field Searches – Properties and Implications „ Cluster Searches – Properties and Future Prospects „ Extrasolar Earths Collaborators

„ Chris Burke (OSU) „ Darren DePoy (OSU) „ Susan Dorsher (OSU) „ Andrew Gould (OSU) „ Joel Hartman (CfA) „ Matt Holman (CfA) „ Gabriela Mallen-Ornelas (CfA) „ Joshua Pepper (OSU) „ Sara Seager (DTM) „ Kris Stanek (CfA) Jargon

„ AU – Astronomical Unit. AU =1.50×1013cm ‹ Mean Earth-Sun Distance pc = 3.09×1018 cm „ pc – “Parallax Second”

‹ Distance at which an object’s parallax would subtend one second of arc

„ Metallicity

‹ Mass fraction of elements above He

„ Main Sequence/Giant Star Constants

33 10 M Sun =1.99×10 g RSun = 6.96×10 cm 30 −3 9 M J =1.90×10 g ≈10 M Sun RJ = 7.15×10 cm ≈ 0.1RSun 27 −6 8 M ⊕ = 5.97×10 g ≈ 3×10 M Sun R⊕ = 6.38×10 cm ≈ 0.01RSun Star Formation 101

„ Molecular Cloud

„ Cores

„ Collapse

„ Ignition/Outflow

„ Protoplanetary Disk

„ Planetary System

Hogerheijde 1998 Planet Formation 101

„ Core-accretion Model

„ Dust Æ Planetesimals (non G)

„ Planetesimals Æ Protoplanets

„ Protoplanets Æ Gas Giants (Outer Solar System)

„ Protoplanets Æ Terrestrial Planets (Inner Solar System) Predictions

„ Three types of Planets ‹ Terrestrial Planets ‹ Gas Giants ‹ Ice Giants „ Segregation in Mass/Separation

(Ida & Lin 2004) Predictions

„ Three types of Planets ‹ Terrestrial Planets ‹ Gas Giants ‹ Ice Giants „ Segregation in Mass/Separation Reality

„ Close-In Planets Æ ‘Hot Jupiters’ „ Cannot have formed in situ „ How did they acquire their strange real estate? Migration

„ Four Classes of Migration:

‹ Type 0 –  Grains • Gas Drag • PR Drag • Yarkovsky Drag

‹ Type I –  Protoplanets • Disk-Planet Torque

‹ Type II –  Planets – Gap • Accretion

‹ Type III – Frederic Masset  Planets – Partial Gap Open Questions

„ What halts planetary migration?

„ Which types of migration are most important?

„ Migration ÅÆ Formation

„ Migration ÅÆ Physical Properties Close-In Planets

„ Pile-Up at P ~ 3 days

„ Dearth of Planets with P < 3 days

„ Lack of High-Mass, Close-In Planets

„ ‘Hot Neptunes’ with P < 3 days

„ Massive, very close-in ‘Very Hot Neptunes’ Transits - Observables

Given a small transit signature, what can we learn? „ Can we tell that it’s a planet? „ Can we measure its radius, separation (semi- major axis)? Transits - Observables

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r F Time Transits - Observables

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r F Time Transits – Parameters

•Depth Measure 2 Infer ⎛ Rp ⎞ δ = ⎜ ⎟ ⎝ R* ⎠ δ ,tT , P •Duration RP ,a

θ* 2 tT ≅ 2 1− b µ*

R* P 2 = 1− b µ* a π bθ* •Period

2π 3/ 2 P = a θ* GM * Stars 101

„ Main Sequence ‹ H Burning 7 / 2 R* ∝ M , L* ∝ M

„ Giants ‹ Exhausted H ‹ Burning He or H in shell „ L,T Æ M,R,density „ Flux, Color Æ L,T ‹ Need d, extinction. „ Spectrum Æ (T,g) „ Cluster Æ d,extinction Transits – Parameters 2 ⎛ R p ⎞ δ = ⎜ ⎟ ⎝ R* ⎠ Measure Infer R P t = * 1− b T a π

2π 3/ 2 δ ,tT , P 0 P = a GM *

δ ,tT , P,b ρ*;(M*, R*);Rp ,a (Accurate LC, M-R Relation)

δ ,tT , P;(T, g) (M*, R*);Rp ,a (Spectroscopic Data) Transits – RV Follow-Up

Low Mass Æ High Mass Æ Degeneracy Ideal Gas + Ion Pressure Pressure H-burning Limit R ∝ M −1/3 R ∝ M Pont et al. 2005 Need to measure mass of the planet – Radial Velocity

−1/3 −2/3 28.4m/s ⎛ M sin i ⎞⎛ P ⎞ ⎛ M ⎞ K = ⎜ p ⎟⎜ ⎟ ⎜ * ⎟ 2 1/ 2 ⎜ ⎟⎜ ⎟ ⎜ ⎟ (1− e ) ⎝ M J ⎠⎝1yr ⎠ ⎝ M sun ⎠ Transits – Detection

„ What is required to detect a planet orbiting a star via transits?

„ What is the probability of detecting a planet around a star?

„ How precise to my measurements need to be?

„ How many stars to I need to look at?

„ How long do I have to look at these stars? Transits – Detection

P = PT PQ PW Gaudi (2000)

Probability that Planet Transits PT PQ Probability of Exceeding S/N Requirement

Probability of Transit(s) Occurring in Window PW Transits – Detection

P = PT PQ PW

a i

cos imin d (cos i) ∫ R + R R P = 0 = * p ≈ * T 1 a a ∫ d (cos i) 0 Transits – Detection

P = PT PQ PW

S/N = Signal to Noise Ratio Must exceed some threshold

σ S δ = N 1/ 2 δ N t σ Transits – Detection

P = PT PQ PW

2 ⎛ Rp ⎞ δ = ⎜ ⎟ ≤1% ⎝ R* ⎠

S −1/2 2 −3/2 1/2 −1 R* Nt = Ntot ∝ a R R L d πa N p * *

σ ∝ F −1/ 2 ∝ L−1/ 2d Transits – Detection

P = PT PQ PW

“Window” Probability- probability that 2 transits occur during the observation windows.

< P > 19 nights 10× W 3−11 10 nights N < PW >3−11 R Duty Cycle= * ≤ 5% πa Transits – Detection

P = PT PQ PW

PT ≈ 8% (3d

PW ≈ 20% (3d

⎛ P ⎞⎛ N* ⎞⎛ fa<0.1AU ⎞ Ndet = fN*P ≈1⎜ ⎟⎜ ⎟⎜ ⎟ ⎝1.6% ⎠⎝104 ⎠⎝ 0.5% ⎠ Transits – Requirements

„ Confirmation and Parameter Estimation ‹ Accurate Light Curves ‹ Follow-up  Spectroscopic  Radial Velocity „ Detection ‹ Many Stars ‹ Accurate Photometry ‹ Lots of Observing Time „ Why Bother? ‹ Possible Using Small Telescopes ‹ Distant Targets ‹ Large Fields of View + Dense Stellar Fields ‹ Rare Objects, Distinct Populations Transits – Flavors Bright Targets • RV Follow-up • All-Sky Amenable to Follow-up Intermediate Targets RV, Oblateness, Atmospheres, •Large FOV Rings, Moons, etc. STARE, Vulcan, WASP Faint Targets • Field Stars (Galactic Disk) Not Amenable to Follow-up EXPLORE, OGLE Primaries too faint for detailed follow-up •Clusters Masses and Radii only. PISCES, EXPORT, STEPSS Why? Statistics! Radial Velocity Surveys

−1/3 −2/3 ~3000 FGKM Stars 28.4m/s ⎛ M sin i ⎞⎛ P ⎞ ⎛ M ⎞ K = ⎜ p ⎟⎜ ⎟ ⎜ * ⎟ 2 1/ 2 ⎜ ⎟⎜ ⎟ ⎜ ⎟ 123 Planets Found (1− e ) ⎝ M J ⎠⎝1yr ⎠ ⎝ M sun ⎠ One Planet with P<3: P = 2.55d Single Measurement Precision K =1m/s − 3m/s

Complete to K ≈ 20m/s M p sin i ≥ 0.2M J for P < 9d Field Surveys - OGLE

5 4 Planets Found by OGLE

Discovered Very Hot Jupiters P ≈1d Radial Velocity vs. Transits

Very Hot Jupiters: Round 1 Very Hot Jupiters: 1 3 Hot Jupiters: Hot Jupiters: 15 1 r =1/15 ≈ 0.07 r = 3/1 = 3 Inconsistency? Very Hot Jupiters not real? Transit Surveys Bogus? Different Populations? Sensitivity of a S/N-Limited Survey

3 Ωdmax N = Pt fnVmax = Pt fn 3 dmax Transit Probability R P = * ∝ P−2/3 t a Signal-to-Noise

S −1/ 2 −1 −1/3 −1 n ∝ a d ∝ P d N At Limiting Signal-to-Noise:

−1/3 −2/3 dmax ∝ P and Pt ∝ P Sensitivity of a S/N-Limited Survey

d ∝ P−1/3 P ∝ P−2/3 max and t dmax (P1)

3 N ∝ Pt fdmax

dmax (P2 )

3 −5/3 N ∝ f (P)Pt dmax ∝ f (P)P Transit surveys are ~6 times more sensitive to 1 day period planets than 3 day period planets! Radial Velocity vs. Transits

Very Hot Jupiters: Round 2 Very Hot Jupiters: 1 3 Hot Jupiters: Hot Jupiters: 15 1 r =1/15 ≈ 0.07 r = 3/(1×6) = 0.5

Still Inconsistent? Radial Velocity vs. Transits

Round 3 Poisson Distribution e−M M N P(N | M ) = N!

+0.10 +1.5 r = 0.07−0.05 r = 0.5−0.3 Radial Velocity vs. Transits 005 2 Gaudi, Seager, & Mallen-Ornelas Relative Frequency of VHJ to HJ is ~ 10-20% Radial Velocity vs. Transits Additional Biases Implications

• VHJ ~ transiting HJ

• One in ~500-1000 FGK Stars has a VHJ

• VHJs more massive? 2 x R • RV VHJ? (HD 73256b) oc he L • Different (mass-dependent) imit parking mechanisms?

• Neptune-mass planets? (influenced by companions?) Searches toward Stellar Systems

Advantages: Disadvantages: •Primaries have common properties •Relatively Faint Stars Explore the effects of: Follow-up difficult Stellar Density •Small Number of Stars Age Difficult to probe f<5% Metallicity [Fe/H]>0 •Primaries have known properties Requirements: Statistics easy. •Many (20) Consecutive Nights Avoid many false positives. •Relatively Large FOV •Compact systems •Modest Aperture Point-and-shoot Survey for Transiting Extrasolar Planets in Stellar Systems (STEPSS) (Open Clusters)

Setup •MDM 1.3m & 2.4m •8192x8192 4x2 Mosaic CCD •25x25 arcmin^2 •0.18”/pixel

NGC1245 •19 nights •1 Gyr •[Fe/H]~0.0

Members: Chris Burke, S.G., Darren DePoy, Rick Pogge Searches toward Stellar Systems

•4-5 minute sampling

•15 nights with data

•9 full nights

•0 photometric nights

Burke et al., in prep Searches toward Stellar Systems

•Sensitive to Jupiters for G0 K0 K5 M0 G0-M0 primaries

~1000 cluster members S ∝ a −1/ 2 R 2 R −3/ 2 L1/ 2d −1 N p * * Main-Sequence Stars

7 / 2 R* ∝ M , L* ∝ M

At Fixed a, R p , d S ∝ R −3/ 2 L1/ 2 ∝ M 1/ 4 N * * * Searches toward Stellar Systems Searches toward Stellar Systems

Period = 2.77 days, Depth ~ 4% Grazing Binary Searches toward Stellar Systems

„ NGC 1245 ‹ Efficiency Calculation Underway ‹ <5% VHJ, <30% HJ. „ NGC 2099 ‹ 37 nights ‹ ~3000 Stars ‹ Improved Statistics „ NGC 2682 (M67) ‹ 20 nights ‹ ~2000 Stars „ Future ‹ 1-2 More Clusters Future Prospects – Hot Neptunes? Future Prospects – Hot Neptunes?

„ Hot Neptunes R ≈ 0.04R N Sun 1.2m δ ≈ 2×10−3 ‹ <0.1% Photometry

„ Large Telescopes ‹ MMT 6.5m r te 6.5m pi ‹ NGC 6791 Ju ‹ Better than 0.1% ne tu ep N

Joel Hartman, Kris Stanek, Matt Holman, S.G Future Prospects – Hot Neptunes?

er pit Ju

ne ptu Ne

Joel Hartman, Kris Stanek, Matt Holman, S.G Future Prospects – Hot Neptunes?

„ Very Hot Neptune Search

‹ Cluster Selection

‹ ~20 Nights on MMT (or 6m Telescope)

‹ Rising Mass Function? Conclusions:

„ Transiting planets can tell us about migration Æ planet formation. „ Consideration of transit basics reveals: ‹ Require accurate photometry ‹ Follow-up for characterization & confirmation ‹ Require ~10,000 stars ‹ Long observational campaigns „ Understanding Field Surveys ‹ RV and TR Surveys Consistent ‹ VHJ are uncommon „ Hot Neptunes within reach. Future Prospects – Extrasolar Earths?

(Ida & Lin 2004) Future Prospects – Extrasolar Earths? Radial Velocity: Next Generation Survey? • 1 m/s limit? -hard + ground based, flexible,cheap, unlimited observing time, nearby stars (TPF) Astrometry: SIM • 1 µas limit - space-based, very expensive, hard to confirm + flexible, nearby stars (TPF) Transits: Kepler - spaced-based, expensive, distant stars, very difficult to confirm +habitable, simple Microlensing: MPF, Ground Based? -expensive, distant stars, impossible(?) to confirm +very low mass planets, robust statistics, many detections Direct: TPF, Darwin Future Prospects – Extrasolar Earths? Comparison with other EarthEarth--massmass planetplanet sensitivitiessensitivities Comparison to other methods. •methodsSIM: 2000 hrs over 5 years, •P=3yr,SIM: 1P=3yr,µas systematic 2000 hours limit. over 5 •years,Kepler: σ=1 µPlanetas. in habitable zone, •KeplerKepler:parameters.Habitable zone, Kepler optimized parameters •RV: Four dedicated 2m telescopes •RV: P=0.5yr, four dedicated 2m over Epsilon5 years, (60,000 Eridani: hrs), S/N P=0.5yr ~13 telescopes, 60,000 hrs, σ=1m/s •Microlensing: a=2.5AU. •Microlensing: a=2.5AU “realistic” optimized “conventional” What S/N threshold? Conventionally: S/N ~ 8

Realistic: S/N ~25

(Gould, Gaudi, & Han 2004) Optimization Future Prospects – Extrasolar Earths? Comparison with other EarthEarth--massmass planetplanet sensitivitiessensitivities methods, cont.

•Every star has a Earth-mass planet with period P •Each technique is confronted with the same ensemble of planetary systems.

Even under optimistic assumptions, only ~5 Earth-mass planets with P=1 year detected with S/N > 25!

Efforts can and should be made to ensure and improve these statistics.

(Gould, Gaudi, & Han 2004) Conclusions:

„ Earths are Hard