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Spin-Orbit Alignment Angles and Planetary Migration of Jovian Exoplanets

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

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Spin-Orbit Alignment Angles and Planetary Migration of Jovian Exoplanets

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  1. Spin-Orbit Alignment Angles andPlanetary Migration of Jovian Exoplanets Norio Narita National Astronomical Observatory of Japan

  2. 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 • Summaryand conclusions

  3. 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

  4. 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

  5. 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!

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

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

  8. Standard Migration Models Type I and II migration mechanisms • 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

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

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

  11. 0 30 60 90 120 150 180 deg Example of Misalignment Prediction Misaligned and even retrograde planets are predicted. Nagasawa, Ida, & Bessho (2008) How can we testthese models by observations?

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

  13. The first exoplanetary transits Charbonneau+ (2000) for HD209458b

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

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

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

  17. 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)

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

  19. Previous studies • HD209458 Queloz+ 2000, Winn+ 2005 • HD189733Winn+ 2006 • TrES-1 Narita+ 2007 • HAT-P-2 Winn+ 2007, Loeillet+ 2008 • HD149026 Wolf+ 2007 • HD17156 Narita+ 2008,2009, Cochran+ 2008, Barbieri+ 2009 • TrES-2 Winn+ 2008 • CoRoT-2 Bouchy+ 2008 • XO-3 Hebrard+ 2008, Winn+ 2009 • HAT-P-1Johnson+ 2008 • HD80606Moutou+ 2009, Pont+ 2009, Winn+ 2009 • WASP-14Joshi+ 2008, Johnson+ 2009 • HAT-P-7 Narita+ 2009, Winn+ 2009 • WASP-17 Anderson+ 2009 • CoRoT-1 Pont+ 2009 • TrES-4 Narita+ to be submitted Red: Eccentric Blue: Binary Green: Both

  20. Subaru Radial Velocity Observations HDS Subaru Iodine cell

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

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

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

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

  25. Misaligned Eccentric Planet: WASP-14b Johnson et al. (2009) λ = -33.1 ± 7.4 deg

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

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

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

  29. Another Retrograde Exoplanet: WASP-17b Andersonet al. (2009)

  30. 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)

  31. 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

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