Aligned, Tilted , Retrograde E xoplanets and their Migration Mechanisms

1. Aligned, Tilted, Retrograde Exoplanetsand their Migration Mechanisms Norio Narita (JSPS Fellow) National Astronomical Observatory of Japan

2. I am a transit observer. I am a transit observer “A transit of the Moon” observed on July 22, 2009 at Hangzhou, China Photo by Norio Narita / Canon EOS Kiss X-2

3. I am working on • Measurements of the Rossiter-McLaughlin effect for transiting planetary systems • High-contrast direct imaging for tilted or eccentric (transiting) planetary systems • Transmission spectroscopy for transiting planets to detect exoplanetary atmospheres • Measurements of transit timing variations of HAT-P-13b Today’s talk

4. Outline • Brief overviewof orbits of Solar System bodies • Orbits ofexoplanets and their migration models • The Rossiter-McLaughlin effect and observations • High-contrast direct imaging for tilted or eccentric planetary systems • Summary

5. Orbits of the Solar System Planets

6. Orbits of the Solar System Planets • All Solar System 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 a proto-planetary disk

7. Orbits of Jovian Satellites

8. Orbits of Solar System Asteroids and Satellites • Asteroids • most of asteroids orbits in the ecliptic plane • significant portion of asteroids have tilted orbits • dozens ofretrograde asteroids have been discovered • 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) • Tilted or retrograde orbits are common for those bodies and are explained by scattering with other bodies etc

9. Motivation to study exoplanetary orbits 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!

10. Outline • Brief overviewof orbits of Solar System bodies • Orbits ofexoplanets and their migration models • The Rossiter-McLaughlin effect and observations • High-contrast direct imaging for tilted or eccentric planetary systems • Summary

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

12. Standard Migration Models Type I and II migration mechanisms • consider gravitational interaction between • proto-planets and proto-planetary disk • 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

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

14. Migration Models for Eccentric Planets • consider gravitational interaction between • planet-planet (planet-planet scattering models) • planet-binary companion (Kozaimigration) captured planets ejected planet

15. Kozai mechanism caused by perturbation from a distant companion and angular momentum conservation orbit 1: low eccentricity and high inclination orbit 2: high eccentricity and low inclination star binary orbital plane companion originally for planet-satellite system (Kozai 1962)

16. Migration Models for Eccentric Planets • consider gravitational interaction between • planet-planet (planet-planet scattering models) • planet-binary companion (Kozaimigration) • may be able to explain the whole orbital distribution • e.g., Nagasawa+ 2008, Fabrycky & Tremaine 2007 • predict a variety of eccentricities • and also predict misalignments between stellar-spin and planetary-orbital axes

17. Examples of Obliquity Prediction Tiltedand even retrograde planets are predicted. Morton & Johnson (2010) How can we testthese models by observations?

18. Outline • Brief overviewof orbits of Solar System bodies • Orbits ofexoplanets and their migration models • The Rossiter-McLaughlin effect and observations • High-contrast direct imaging for tilted or eccentric planetary systems • Summary

19. 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.

20. 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.

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

22. Observable parameter λ： sky-projected angle between the stellar spin axis and the planetary orbital axis (e.g., Ohta+ 2005, Gaudi & Winn 2007, Hirano et al. 2010)

23. Subaru HDS Observations since 2006 HDS Subaru Iodine cell

24. What we got retrograde aligned aligned TrES-1b: Narita et al. (2007) HD17156b: Narita et al. (2009a) HAT-P-7b: Narita et al. (2009b) aligned tilted tilted XO-4b: Narita et al. (2010c) TrES-4b: Narita et al. (2010a) HAT-P-11b: Hirano et al. (2010b)

25. Discovery of Retrograde Orbit: HAT-P-7b NN et al. (2009b) Subaru observation through UH time Winn et al. (2009c)

26. First RM Measurement forSuper-Neptune Planet：HAT-P-11b Hirano et al. (2010b)

27. Results of Previous Observations • Our group: Subaru telescope • 13 targets observed • 7 papers published and 3 papers are in prep. • 5 out of 13 planets have tilted or retrograde orbit! • US: Keck telescope, UK, France: HARPS at 3.6m telescope • over 30 targets observed • similar percentage planets have tilted or retrograde orbit • now statistically assured

28. What we learned from RM measurements Stellar Spin PlanetaryOrbit • Tilted or retrograde planets are not rare • p-p scattering or Kozai mechanism occur in exoplanetary systems

29. Remaining Problems Which model is a dominant migration mechanism? Morton & Johnson (2010) The number of samples is still insufficient to answer statistically.

30. Remaining Problems • One cannot distinguish between p-p scattering and Kozaimigration for each planetary system • To specify a planetary migration mechanism for each system, we need to search for counterparts of migration processes • long term radial velocity measurements (< 10AU) • direct imaging (> 10-100 AU)

31. Outline • Brief overviewof orbits of Solar System bodies • Orbits ofexoplanets and their migration models • The Rossiter-McLaughlin effect and observations • High-contrast direct imaging for tilted or eccentric planetary systems • Summary

32. Motivation for high-contrast direct imaging • The results of the RM effect encourage direct imaging because • a significant part of planetary systems may have wide separation massive bodies (e.g., scattered massive planets or brown dwarfs, or binary companions) • direct imaging for tilted or eccentric planetary systems may allow us to specify a migration mechanism for each planetary system

33. An example of this study: Target HAT-P-7 • not eccentric, but retrograde (NN+ 2009b, Winn et al. 2009c) NN et al. (2009b) Winn et al. (2009c) very interesting target to search for outer massive bodies

34. Subaru’s new instrument: HiCIAO • HiCIAO: High Contrast Instrument for next generation Adaptive Optics • PI: Motohide Tamura (NAOJ) • Co-PI: Klaus Hodapp (UH), Ryuji Suzuki (TMT) • 188 elements curvature-sensing AO and will be upgraded to SCExAO (1024 elements) • Commissioned in 2009 • Specifications and Performance • 2048x2048 HgCdTe and ASIC readout • Observing modes: DI, PDI (polarimetric mode), SDI (spectral differential mode), & ADI; w/wo occulting masks (>0.1") • Field of View: 20"x20" (DI), 20"x10" (PDI), 5"x5" (SDI) • Contrast: 10^-5.5 at 1", 10^-4 at 0.15" (DI) • Filters: Y, J, H, K, CH4, [FeII], H2, ND • Lyot stop: continuous rotation for spider block

35. Observations • Subaru/HiCIAO Observation: 2009 August 6 • Setup: H band, DI mode (FoV: 20’’ x 20’’) • Total exposure time: 9.75 min • Angular Differential Imaging (ADI: Marois+ 06) technique with Locally Optimized Combination of Images (LOCI: Lafreniere+ 07) • Calar Alto / AstraLux Norte Observation: 2009 October 30 • Setup: I’ and z’ bands, FoV: 12’’ x 12’’ • Total exposure time: 30 sec • Lucky Imaging technique (Daemgen+ 09)

36. Result Images N NN et al. (2010b) E Left: Subaru HiCIAO image, 12’’ x 12’’, Upper Right: HiCIAO LOCI image, 6’’ x 6’’ Lower Right: AstraLux image, 12’’ x 12’’

37. Characterization of binary candidates projected separation: ~1000 AU Based on stellar SED (Table 3) in Kraus and Hillenbrand (2007). Assuming that the candidates are main sequence stars at the same distance as HAT-P-7.

38. Can these candidates cause Kozai migration? • The perturbation of a binary must be the strongest in the system to cause the Kozai migration (Innanen et al. 1997) • If perturbation of another body is stronger • Kozaimigraionrefuted • If such an additional body does not exist • both Kozai and p-p scattering still survive

39. An additional body ‘HAT-P-7c’ Winn et al. (2009c) 2008 and 2010 Subaru data (unpublished) 2007 and 2009 Keck data HJD - 2454000 Long-term RV trend ~20 m/s/yr is ongoing from 2007 to 2010 constraint on the mass and semi-major axis of ‘c’ (Winn et al. 2009c)

40. Result for the HAT-P-7 case • We detected two binary candidates, but the Kozaimigration was excluded because perturbation by the additional body is stronger than that by companion candidates • As a result, we conclude that p-p scattering is the most likely migration mechanism for this system

41. Ongoing and Future Subaru Observations • There are numbers of tilted and/or eccentric transiting planets • These planetary systemsare interesting targets that we may be able to discriminate planetary migration mechanisms • No detection is still interesting to refute Kozai migration • Detections of outer massive bodies are very interesting • but It would take some time to confirm such bodies

42. Waiting 2nd Epoch and more… speckle?

43. Summary • RM measurements have discovered numbers of tilted and retrograde planets • Tilted or eccentric planets are explained by p-p scattering or Kozai migration --> those mechanisms are not rare • One problem is that we cannot distinguish between p-p scattering and Kozai migration from orbital tilt or eccentricity • High-contrast direct imaging can resolve the problem and may allow us to specify migration mechanism for each system • Further results will be reported in the near future!

46. Howto constrain migration mechanism • Step 1: Is there a binary candidate? • No • Kozai migration by a binary companion is excluded • If a candidate exist → step 2 • both p-p scattering and Kozai migration survive • need a confirmation of true binary nature • common proper motion • common peculiar radial velocity • common distance (by spectral type)

47. How to constrain migration mechanism • Step 2: calculate restricted region for Kozai migration • The Kozai migration cannot occur if the timescale of orbital precession due to an additional body PG,c is shorter than that caused by a binary through Kozai mechanism PK,B (Innanen et al. 1997) • If any additional body exists in the restricted region • Kozaimigraion excluded • search for long-term RV trend is very important • If no additional body is found in the region • both Kozai and p-p scattering still survive

48. SEEDS Project • SEEDS: Strategic Exploration of Exoplanets and Disks with Subaru • First “Subaru Strategic Observations” PI: Motohide Tamura • Using Subaru’s new instruments: HiCIAO & AO188 • total 120 nights over 5 years (10 semesters) with Subaru • Direct imaging and census of giant planets and brown dwarfs around solar-type stars in the outer regions (a few - 40 AU) • Exploring proto-planetary disks and debris disks for origin of their diversity and evolution at the same radial regions • I am working in a sub-category of known planetary systems, especially targeting for tilted or eccentric planetary systems

49. Future AO upgrade: SCExAO from 2011Subaru Coronagraphic Extreme-AO System AO188 limit SCExAO limit

50. Remaining Problems • Correlation with properties of planet and host star • Need to observe more targets for statistics. • One cannot distinguish between p-p scattering and Kozaimigration for each system • Need to search for counterparts of migration processes • long term radial velocity measurements (< 10AU) • direct imaging (> 10-100 AU)