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

 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 Need planetary migration mechanisms! Snow line Jupiter

Standard Migration Models  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 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) ejected planet captured planets

Kozai mechanism companion star orbit 1: low eccentricity and high inclination orbit 2: high eccentricity and low inclination binary orbital plane caused by perturbation from a distant companion and angular momentum conservation 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. How can we test these models by observations? Morton & Johnson (2010)

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 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 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 a 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, Gaudi & Winn 2007, Hirano et al. 2010)

Subaru HDS Observations since 2006 Iodine cell HDS Subaru

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

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 Winn et al. (2009c) observed on July 1, 2009 Subaru observation through UH time

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

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

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

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

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

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 (> 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) very interesting target to search for outer massive bodies NN et al. (2009b) Winn et al. (2009c)

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

Characterization of binary candidates 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. projected separation: ~1000 AU

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’ HJD Winn et al. (2009c) 2008 and 2010 Subaru data (unpublished) 2007 and 2009 Keck data 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!