Spin-Orbit Alignment Angles and Planetary Migration of Jovian Exoplanets Norio Narita National Astronomical Observatory of Japan

Outline Brief review of orbits of Solar System bodies Introduction of exoplanets and migration models How to measure spin-orbit alignment angles of exoplanets Previous observations and results Summary and conclusions

Orbits of the Solar System Planets  All planets orbit in the same direction  small orbital eccentricities At a maximum (Mercury) e = 0.2  small orbital inclinations The spin axis of the Sun and the orbital axes of planets are aligned within 7 degrees In almost the same orbital plane (ecliptic plane)  The configuration is explained by core-accretion models in proto-planetary disks

Orbits of Solar System Asteroids and Satellites  Asteroids most of asteroids orbits in the ecliptic plane significant portion of asteroids have tilted orbits 24 retrograde asteroids have been discovered so far  Satellites orbital axes of satellites are mostly aligned with the spin axis of host planets dozens of satellites have tilted orbits or even retrograde orbits (e.g., Triton around Neptune)  These highly tilted or retrograde orbits are explained by gravitational interaction with planets or Kozai mechanism

Motivation Orbits of the Solar System bodies reflect the formation history of the Solar System How about extrasolar planets? Planetary orbits would provide us information about formation histories of exoplanetary systems!

First discovered in 1995, by Swiss astronomers (below) So far, over 400 candidates of exoplanets have been found at 10 th anniversary conference Left: Didier Queloz Right: Michel Mayor Introduction of Exoplanets

Semi-Major Axis Distribution of Exoplanets Need planetary migration mechanisms! Snow line Jupiter

Standard Migration Models  consider gravitational interaction between proto-planetary disk and planets Type I: less than 10 Earth mass proto-planets Type II: more massive case (Jovian planets)  well explain the semi-major axis distribution e.g., a series of Ida & Lin papers  predict small eccentricities and small inclination for migrated planets Type I and II migration mechanisms

Eccentricity Distribution Cannot be explained by Type I & II migration model Jupiter Eccentric Planets

Migration Models for Eccentric Planets  consider gravitational interaction between planet-planet (planet-planet scattering models) planet-binary companion (Kozai migration)  may be able to explain eccentricity distribution e.g., Nagasawa+ 2008, Chatterjee  predict a variety of eccentricities and also misalignments between stellar-spin and planetary-orbital axes ejected planet

Example of Misalignment Prediction deg Nagasawa, Ida, & Bessho (2008) Misaligned and even retrograde planets are predicted. How can we test these models by observations?

Planetary transits 2006/11/9 transit of Mercury observed with Hinode transit in the Solar System If a planetary orbit passes in front of its host star by chance, we can observe exoplanetary transits as periodical dimming. transit in exoplanetary systems (we cannot spatially resolve) slightly dimming

The first exoplanetary transits Charbonneau+ (2000) for HD209458b

Transiting planets are increasing So far 62 transiting planets have been discovered.

The Rossiter-McLaughlin effect the planet hides the approaching side → the star appears to be receding the planet hides the receding side → the star appears to be approaching planet star When a transiting planet hides stellar rotation, radial velocity of the host star would have an apparent anomaly during transits.

What can we learn from RM effect? Gaudi & Winn (2007) The shape of RM effect depends on the trajectory of the transiting planet. well aligned misaligned Radial velocity during transits = the Keplerian motion and the RM effect

Observable parameter λ ： sky-projected angle between the stellar spin axis and the planetary orbital axis (e.g., Ohta+ 2005, Gimentz 2006, Gaudi & Winn 2007)

Note: orbital inclination Sun’s equatorial plane planetary orbital plane Sun’s spin axis Earth planetary orbital plane line of sight from the Earth normal vector of line of sight orbital inclination in the Solar System orbital inclination in exoplanetary science spin-orbit alignment angle in exoplanetary science

 HD Queloz+ 2000, Winn  HD Winn  TrES-1 Narita  HAT-P-2 Winn+ 2007, Loeillet  HD Wolf  HD17156 Narita+ 2008,2009, Cochran+ 2008, Barbieri  TrES-2 Winn  CoRoT-2 Bouchy  XO-3 Hebrard+ 2008, Winn  HAT-P-1 Johnson  HD80606 Moutou+ 2009, Pont+ 2009, Winn  WASP-14 Joshi+ 2008, Johnson  HAT-P-7 Narita+ 2009, Winn  WASP-17 Anderson  CoRoT-1 Pont  TrES-4 Narita+ to be submitted Previous studies Red: Eccentric Blue: Binary Green: Both

Subaru Radial Velocity Observations Iodine cell HDS Subaru

Prograde Planet: TrES-1b Our first observation with Subaru/HDS Thanks to Subaru, clear detection of the Rossiter effect. We confirmed a prograde orbit and the spin-orbit alignment of the planet. NN et al. (2007)

Aligned Ecctentric Planet: HD17156b Well aligned in spite of its eccentricity. Eccentric planet with the orbital period of 21.2 days. NN et al. (2009a) λ = 10.0 ± 5.1 deg

Aligned Binary Planet: TrES-4b NN et al. in prep. Well aligned in spite of its binarity. NN et al. in prep. λ = 5.3 ± 4.7 deg

Misaligned Eccentric Planet: XO-3b Winn et al. (2009a) λ = 37.3 ± 3.7 deg Hebrard et al. (2008) λ = 70 ± 15 deg

Misaligned Eccentric Planet: WASP-14b Johnson et al. (2009) λ = ± 7.4 deg

Misaligned Binary Planet: HD80606b Winn et al. (2009b) λ = 53 (+34, -21) deg Pont et al. (2009) λ = 50 (+61, -36) deg

Retrograde Exoplanet: HAT-P-7b NN et al. (2009b) Winn et al. (2009c)

Note: Implication of the results Planetary system seen from the Earth We have not yet learned the inclination of the stellar spin axis Earth The planet is in a retrograde orbit when seen from the Earth The true spin-orbit alignment angle will be determined when the Kepler photometric data are available (by asteroseismology)

Another Retrograde Exoplanet: WASP-17b Anderson et al. (2009)

Summary of RM Studies  Exoplanets have a diversity in orbital distributions  We can measure spin-orbit alignment angles of exoplanets by spectroscopic transit observations 4 out of 6 eccentric planets have highly tilted orbits  spin-orbit misalignments may be common for eccentric planets 2 out of 10 non-eccentric planets also show misaligned orbits  spin-orbit misalignements are rare for non-eccentric planets  we can add samples to learn a statistical population of alinged/misaligned/retrograde planets (future task)

Conclusions and Future Prospects  Recent observations support planetary migration models considering not only disk-planet interactions, but also planet- planet scattering and the Kozai migration  The diversity of orbital distributions would be brought by the various planetary migration mechanisms  We will be able to conduct similar studies for extrasolar terrestrial planets in the future