Observational Studies for Understanding Planetary Migration

1. Observational Studies forUnderstanding Planetary Migration Norio Narita National Astronomical Observatory of Japan

2. Relation to Prof. Miyama • Based on “Astronomer’s family tree in Japan” • Prof. Miyama was “brother” of Prof. Katsuhiko Sato • My lab at Univ. of Tokyo: UTAP • Prof. Yasushi Suto was my supervisor at School of Science • Prof. Katsuhiko Sato was my supervisor at School of Education • So Prof. Miyama is my “uncle” researcher

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

4. Orbits of the Solar System Planets

5. 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

6. Orbits of Jovian Satellites

7. Orbits of Solar System Asteroids and Satellites • Asteroids • most of asteroids orbits in the ecliptic plane • significant portion of asteroids have tilted orbits • dozens of retrograde 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

8. 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!

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

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

11. 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

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

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

14. 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)

15. 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

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

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

18. 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.

19. 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.

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

21. 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)

22. Subaru HDS Observations since 2006 HDS Subaru Iodine cell

23. 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)

24. Papers from the Subaru Telescope • S06A-029: Narita+ (2007) • S07A-007: Narita+ (2010a) • S07B-091: Johnson+. (2008), Albrecht+ (2011), Narita+ in prep. • S08A-021: Narita+ (2009b), Narita+ (2011) • S08B-086: Bad weather • S08B-087: Narita+ (2009a) • S09B-089: Narita+ (2010c) • S10A-139: Hirano+ (2011) • S10A-143: Hirano+ (2010b) • S11A-131: Hirano+ in prep. 10 paper published more to come

25. Discovery of Retrograde Orbit: HAT-P-7b NN et al. (2009b) observed on May 30, 2008 Subaru observation through UH time Winn et al. (2009c) observed on July 1, 2009

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

27. What we learned from RM measurements Stellar Spin PlanetaryOrbit • Tilted planets are not rare (1/3 hot Jupiters are tilted) • p-p scattering or Kozai mechanism occur in exoplanetary systems

28. 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 Kozai migration for each system • Need to search for counterparts of migration processes

29. Correlation between λ and Stellar Temperature 8.1 days 111 days Winn et al. (2010) Stellar Convective Layer

30. Scattering or Kozai Which model is a dominant migration mechanism? Morton & Johnson (2010) The number of samples is still insufficient to answer statistically.

31. A Solution for the Problem • One cannot distinguish between p-p scattering and Kozai migration 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)

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

33. 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

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. 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

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 • Kozaimigraion refuted • 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 Kozai migration 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. SEEDS-RV Sub-category • Members: N. Narita, Y. Takahashi, B. Sato, R. Suzuki • Targets: Known planetary systems such as, • Very famous systems • long-term RV trend systems • Giant systems • Eccentric planetary systems • Transiting planetary systems (including eccentric/tilted systems) • 25+ systems observed • including 10+ transiting planetary systems (1st epoch) • some follow-up targets were observed (2nd epoch)

42. 9 Results at a Glance

43. First/Second Year Results • 9 out of 10 systems have companion candidates • high frequency of detecting candidate companions • Caution: this is only 1 epoch -> follow-up needed • Message to transit/secondary eclipse observers • Be careful about contamination of candidate companions, even they are not real binary companions • sometimes they may affect your results • 2nd epoch observations are ongoing

44. Ongoing and Future Subaru Observations • There are numbers of tilted and/or eccentric transiting planets • These planetary systems are 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 • Stay tuned for new results • How about Earth-like planets?

45. Detectability of the Rossiter effect ○：mostly possible, △：partially possible, ×：very difficult

46. Summary • We can study planetary migration by (Subaru) observations • We hope to study planetary migration of all types of planets (Earth-like to Jovian planets) in the future • We need Subaru/IRD and TMT!