Discriminating Migration Mechanisms of Tilted or Eccentric Planetary Systems Norio Narita (NAOJ/University of Hawaii)

Special thanks to my collaborators Measurements of the Rossiter-McLaughlin effect – Teruyuki Hirano, Bun’ei Sato, Josh Winn, Wako Aoki, Motohide Tamura SEEDS NS category/RV sub-category (Today’s talk) – Tomoyuki Kudo, Ryo Kandori, Bun’ei Sato, Ryuji Suzuki, Masayuki Kuzuhara, Yasuhiro Takahashi, Motohide Tamura, and all SEEDS/HiCIAO/AO188 members Photometric transit observations (incl. TTV) – Akihiko Fukui, Takuya Suenaga, Masayuki Kuzuhara, Hiroshi Ohnuki, Bun’ei Sato, Osamu Ohshima, Motohide Tamura, and Japanese Transit Observation Network members

Motivation to study exoplanetary orbits How do planetary systems form? Planetary orbits would provide us information about formation histories of exoplanetary systems!

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

Eccentricity Distribution Need planet-planet scattering and/or Kozai mechanism. Jupiter Eccentric Planets

What we learned from RM measurements  Tilted or retrograde planets are not rare (1/3 planets are tilted)  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 RM 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)

Motivation for high-contrast direct imaging  The results of RM measurements suggest that 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

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

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)

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 conditional equation: (smaller bodies are allowed)  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  We can constrain planetary migration mechanisms by this methodology.

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…

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

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)