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 - Fractional Photometric Deviation O bservables Duration Time = t T Depth = δ Transits - Fractional Photometric Deviation O bservables Period Time = P 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<P<11d, logarithmic) P =1.6% PQ ≈1 PW ≈ 20% (3d<P<11d, logarithmic) ⎛ 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 Relative Frequency of VHJ to HJ is ~ 10-20% Gaudi, Seager, & Mallen-Ornelas 2005 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? Jupiter Neptune 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.