Aligned, Tilted, Retrograde Exoplanets and their Migration Mechanisms Norio Narita (JSPS Fellow) National Astronomical Observatory of Japan

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

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

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

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

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

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

What we learned from RM measurements  Tilted or retrograde planets are not rare  p-p scattering or Kozai mechanism occur in exoplanetary systems Stellar Spin Planetary Orbit

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

Remaining Problems  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

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)

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

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)

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

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 but It would take some time to confirm such bodies

Waiting 2nd Epoch and more… speckle?

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!

How to 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)

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 P G,c is shorter than that caused by a binary through Kozai mechanism P K,B (Innanen et al. 1997)  If any additional body exists in the restricted region Kozai migraion 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

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

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

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

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

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 long term radial velocity measurements (< 10AU) direct imaging (> AU)