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Observational Studies for Understanding Planetary Migration Norio Narita National Astronomical Observatory of Japan 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 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 Orbits of the Solar System Planets 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 Orbits of Jovian Satellites 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 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! 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 Semi-Major Axis Distribution of Exoplanets Snow line Jupiter Need planetary migration mechanisms! 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 Eccentricity Distribution Eccentric Planets Jupiter Cannot be explained by Type I & II migration model Migration Models for Eccentric Planets consider gravitational interaction between planet-planet (planet-planet scattering models) planet-binary companion (Kozai migration) captured planets ejected planet 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) 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 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 Examples of Obliquity Prediction Tilted and even retrograde planets are predicted. Morton & Johnson (2010) How can we test these models by observations? 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 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. The Rossiter-McLaughlin effect When a transiting planet hides stellar rotation, star planet planet the planet hides the approaching side the planet hides the receding side → the star appears to be receding → the star appears to be approaching radial velocity of the host star would have an apparent anomaly during transits. What can we learn from RM effect? The shape of RM effect depends on the trajectory of a transiting planet. well aligned misaligned Radial velocity during transits = the Keplerian motion and the RM effect Gaudi & Winn (2007) 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) Subaru HDS Observations since 2006 HDS Subaru Iodine cell What we got aligned TrES-1b: Narita et al. (2007) aligned retrograde aligned HD17156b: Narita et al. (2009a) HAT-P-7b: Narita et al. (2009b) tilted tilted XO-4b: Narita et al. (2010c) TrES-4b: Narita et al. (2010a) HAT-P-11b: Hirano et al. (2010b) 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 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 First RM Measurement for Super-Neptune Planet：HAT-P-11b Hirano et al. (2010b) What we learned from RM measurements Stellar Spin Planetary Orbit Tilted planets are not rare (1/3 hot Jupiters are tilted) p-p scattering or Kozai mechanism occur in exoplanetary systems 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 Correlation between λ and Stellar Temperature 8.1 days 111 days Winn et al. (2010) Stellar Convective Layer Scattering or Kozai Which model is a dominant migration mechanism? Morton & Johnson (2010) The number of samples is still insufficient to answer statistically. 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) 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 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 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 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 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’’ 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. 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 Kozai migraion refuted If such an additional body does not exist both Kozai and p-p scattering still survive An additional body ‘HAT-P-7c’ Winn et al. (2009c) 2007 and 2009 Keck data 2008 and 2010 Subaru data (unpublished) 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) 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 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) 9 Results at a Glance 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 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? Detectability of the Rossiter effect Current Opt. RV Subaru IRD TMT IR (1m/s) TMT opt. (0.1m/s) F, G, K Jupiter ○ ○ ○ ○ F, G, K Neptune △ △ ○ ○ F, G, K Earth × × × ○ M Jupiter △ ○ ○ ○ M Neptune △ ○ ○ ○ M Earth × △ ○ △ ○：mostly possible, △：partially possible, ×：very difficult 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!