II. Results from Transiting Planets 1. Global Properties 2. The Rossiter-McClaughlin Effect
Planet Radius Most transiting planets tend to be inflated. Approximately 68% of all transiting planets have radii larger than 1.1 R Jup.
Possible Explanations for the Large Radii 1. Irradiation from the star heats the planet and slows its contraction it thus will appear younger than it is and have a larger radius
Possible Explanations for the Large Radii 2. Slight orbital eccentricity (difficult to measure) causes tidal heating of core larger radius Slight Problem: HD 17156b: e=0.68 HD 80606b: e=0.93 CoRoT 10b: e=0.53 R = 1.02 R Jup R = 0.92 R Jup R = 0.97R Jup Caveat: These planets all have masses 3-4 M Jup, so it may not be the smaller radius is just due to the larger mass. 3. We do not know what is going on.
Density Distribution S J/U N Number Density (cgs)
Comparison of Mean Densities Giant Planets with M < 2 M Jup : 0.78 cgs HD 17156, P = 21 d, e= 0.68 M = 3.2 M Jup, density = 3.8 HD 80606, P = 111 d, e=0.93, M = 3.9 M Jup, density = 6.4 CoRoT 10b, P=13.2, e= 0.53, M = 2.7 M Jup, density = 3.7 CoRoT 9b, P = 95 d, e=0.12, M = 1 M Jup, density = 0.93 The three eccentric transiting planets have high mass and high densities. Formed by mergers?
According to formation models of Guenther Wuchterl CoRoT-10 cannot be a planet. It is 2x the highest mass objects that can form in the proto-nebula M Nep M Jup One interpretation: it is the merger of two 1.3 M Jup planets. This may also explain the high eccentricity
Period Distribution for short period Exoplanets p = 13% p = 7% Number Period (Days)
The 3 day period may mark the inner edge of the proto-planetary disk
Mass-Radius Relationship Radius is roughly independent of mass, until you get to small planets (rocks)
Planet Mass Distribution RV Planets Close in planets tend to have lower mass, as we have seen before. Transiting Planets
Number [Fe/H] Metallicity Distribution [Fe/H]
Host Star Mass Distribution Transiting Planets Nmber RV Planets Stellar Mass (solar units)
Magnitude distribution of Exoplanet Discoveries Percent V- magnitude
8.3 days of Hubble Space Telescope Time Expected 17 transits None found This is a statistically significant result. [Fe/H] = 0.7
[Fe/H] = +0.4 Expected number of transiting planets = 1.5 Number found = 0 This is not a statistically significant result.
Summary of Global Properties of Transiting Planets 1. Transiting giant planets (close-in) tend to have inflated radii (much larger than Jupiter) 2. A significant fraction of transiting giant planets are found around early-type stars with masses 1.3 M sun. 3. There appears to be no metallicity-planet connection among transiting planets 4. The period distribution of close-in planets peaks around P 3 days. 5. Most transiting giant planets have densities near that of Saturn. It is not known if this is due to their close proximity to the star (i.e. inflated radius) 6. Transiting planets have been discovered around stars fainter than those from radial velocity surveys
Early indications are that the host stars of transiting planets have different properties than non-transiting planets. Most likely explanation: Transit searches are not as biased as radial velocity searches. One looks for transits around all stars in a field, these are not preselected. The only bias comes with which ones are followed up with Doppler measurements Caveat: Transit searches are biased against smaller stars. i.e. the larger the star the higher probability that it transits
Spectroscopic Transits: The Rossiter-McClaughlin Effect
The Rossiter-McClaughlin Effect 1 2 3 4 +v 1 4 0 2 v 3 The R-M effect occurs in eclipsing systems when the companion crosses in front of the star. This creates a distortion in the normal radial velocity of the star. This occurs at point 2 in the orbit.
The Rossiter-McLaughlin Effect in an Eclipsing Binary From Holger Lehmann
The effect was discovered in 1924 independently by Rossiter and McClaughlin Curves show Radial Velocity after removing the binary orbital motion
The Rossiter-McLaughlin Effect or Rotation Effect For rapidly rotating stars you can see the planet in the spectral line
For stars whose spectral line profiles are dominated by rotational broadening there is a one to one mapping between location on the star and location in the line profile: V = V rot V = +V rot V = 0
Formation of the Pseudo-emission bumps
A Doppler Image of a Planet For slowly rotationg stars you do not see the distortion, but you measure a radial velocity displacement due to the distortion.
The Rossiter-McClaughlin Effect v +v v +v 0 When the companion covers the receeding portion of the star, you see more negatve velocities of the star rotating towards you. You thus see a displacement to negative RV. As the companion crosses the star the observed radial velocity goes from + to (as the planet moves towards you the star is moving away). The companion covers part of the star that is rotating towards you. You see more possitive velocities from the receeding portion of the star) you thus see a displacement to + RV.
The Rossiter-McClaughlin Effect What can the RM effect tell you? 1. The inclination or impact parameter v +v v +v Shorter duration and smaller amplitude
The Rossiter-McClaughlin Effect What can the RM effect tell you? 2. Is the companion orbit in the same direction as the rotation of the star? v +v v +v
λ Orbital plane What can the RM effect tell you? 3. Are the spin axes aligned?
Amplitude of the R-M effect: A RV = 52.8 m s 1 Note: V ( s ) 5 km s 1 A RV is amplitude after removal of orbital mostion V s is rotational velocity of star in km s 1 r is radius of planet in Jupiter radii R is stellar radius in solar radii r R Jup ( ) 2 ( R ) 2 1. The Magnitude of the R-M effect depends on the radius of the planet and not its mass. 2. The R-M effect is proportional to the rotational velocity of the star. If the star has little rotation, it will not show a R-M effect. R סּ
HD 209458 λ = 0.1 ± 2.4 deg
HD 189733 λ = 1.4 ± 1.1 deg
CoRoT-2b λ = 7.2 ± 4.5 deg
HD 147506 Best candidate for misalignment is HD 147506 because of the high eccentricity
On the Origin of the High Eccentricities Two possible explanations for the high eccentricities seen in exoplanet orbits: Scattering by multiple giant planets Kozai mechanism
Planet-Planet Interactions Initially you have two giant planets in circular orbits These interact gravitationally. One is ejected and the remaining planet is in an eccentric orbit
Kozai Mechanism Two stars are in long period orbits around each other. A planet is in a shorter period orbit around one star. If the orbit of the planet is inclined, the outer planet can pump up the eccentricity of the planet. Planets can go from circular to eccentric orbits.
If either mechanism is at work, then we should expect that planets in eccentric orbits not have the spin axis aligned with the stellar rotation. This can be checked with transiting planets in eccentric orbits Winn et al. 2007: HD 147506b (alias HAT-P-2b) Spin axes are aligned within 14 degrees (error of measurement). No support for Kozai mechanism or scattering
What about HD 17156? Narita et al. (2007) reported a large (62 ± 25 degree) misalignment between planet orbit and star spin axes!
Cochran et al. 2008: λ = 9.3 ± 9.3 degrees No misalignment!
TrES-1 λ = 30 ± 21 deg
XO-3-b
Hebrard et al. 2008 λ = 70 degrees
Winn et al. (2009) recent R-M measurements for X0-3 λ = 37 degrees
From PUBL ASTRON SOC PAC 121(884):1104-1111. 2009. The Astronomical Society of the Pacific. All rights reserved. Printed in U.S.A. For permission to reuse, contact journalpermissions@press.uchicago.edu. Fig. 3. Relative radial velocity measurements made during transits of WASP-14. The symbols are as follows: Subaru (circles), Keck (squares), Joshi et al. 2009 (triangles). Top panel: The Keplerian radial velocity has been subtracted, to isolate the Rossiter-McLaughlin effect. The predicted times of ingress, midtransit, and egress are indicated by vertical dotted lines. Middle panel: The residuals after subtracting the best-fitting model including both the Keplerian radial velocity and the RM effect. Bottom panel: Subaru/HDS measurements of the standard star HD 127334 made on the same night as the WASP-14 transit.
From PUBL ASTRON SOC PAC 121(884):1104-1111. 2009. The Astronomical Society of the Pacific. All rights reserved. Printed in U.S.A. For permission to reuse, contact journalpermissions@press.uchicago.edu. Fig. 4. Spin-orbit configuration of the WASP-14 planetary system. The star has a unit radius and the relative size of the planet and impact parameter are taken from the best-fitting transit model. The sky-projected angle between the stellar spin axis (diagonal dashed line) and the planet s orbit normal (vertical dashed line) is denoted by λ, which in this diagram is measured counterclockwise from the orbit normal. Our best-fitting λ is negative. The 68.3% confidence interval for λ is traced on either side of the stellar spin axis and denoted by σλσλ.
Fabricky & Winn, 2009, ApJ, 696, 1230
HAT-P7 λ = 182 deg!
HAT-P7 Evidence for an additional companion
HD 80606
λ = 32-87 deg
HD 15082 = WASP-33 No RV variations are seen, but we can apply the Sherlock Holmes Proof. A companion of radius 1.5 R Jup is either a planet, brown dwarf, or low mass star. The RV variations exclude BD and stellar companion.
The Line Profile Variations of HD 15082 = WASP-33 Pulsations Concern: The planet is not seen in the wings of the line!
RM anomaly HARPS data : F. Bouchy Model fit: F. Pont
HARPS data : F. Bouchy Model fit: F. Pont Lambda ~ 80 deg!
Distribution of spin-orbit axes Red: retrograde orbits
λ (deg) 40% of Short Period Exoplanets show significant misalignments 20% of Short Period Exoplanets are in retrograde orbits What are the implications?
The Hill Criteria is a simple way to assess the stability of planetary systems.
Suppose that Nature fills the parameter space with ultra-compact planets: if it can form a planet it can. If many Giant planets are formed, these will interact and scatter some towards the inner regions. The close-in planets may not be formed by migration at all, but by scattering of planets from the outer to the inner regions of the star. Ultracompact systems can also explain the eccentric close in planets as mergers.