Discriminating Planetary Migration Mechanisms by Direct Imaging

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Discriminating Planetary Migration Mechanisms by Direct Imaging. Norio Narita National Astronomical Observatory of Japan. on behalf of SEEDS/ HiCIAO /AO188 teams. Clues to discriminate migration models. small eccentricity and obliquity disk-planet interaction. orbital eccentricity
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Discriminating Planetary Migration Mechanismsby Direct ImagingNorio NaritaNational Astronomical Observatory of Japanon behalf of SEEDS/HiCIAO/AO188 teamsCluesto discriminate migration modelssmall eccentricity and obliquitydisk-planet interactionorbital eccentricityby radial velocityspin-orbit alignment angleby the RM effect
  • large eccentricity or obliquity
  • planet-planet scattering
  • Kozai migration
  • Can we discriminate two models?
  • Planet-Planet scattering
  • Additional information from direct imaging!
  • Kozai migration
  • We introduce a procedure to discriminatetwo planetary migration models by direct imaging.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
  • Procedure 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)
  • Procedure 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 PG,c is shorter than that caused by a binary through Kozai mechanism PK,B (Innanen et al. 1997)
  • If any additional body exists in the restricted region
  • Kozaimigraion excluded
  • search for long-term RV trend is very important
  • If no additional body is found in the region → step 3
  • both Kozai and p-p scattering still survive
  • Procedure to constrain migration mechanism
  • Step 3: calculate initial condition for Kozai migration
  • Based on angular momentum conservation during Kozai migration, we can constrain the initial condition of the system
  • : initial mutual inclination between the planetary orbit and the binary orbit can be constrained
  • binaryhost starplanetFirst Application: HAT-P-7
  • not eccentric, but misaligned (NN+ 2009, Winn et al. 2009)
  • NN et al. (2009)Winn et al. (2009)very interesting target for direct imaging observation!Step 1: Direct Imaging 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 ImagesNNN et al. (2010)ELeft: Subaru HiCIAO image, 12’’ x 12’’, Upper Right: HiCIAO LOCI image, 6’’ x 6’’Lower Right: AstraLux image, 12’’ x 12’’Constraints on other outer bodiesH band contrast ratio5σ detectable mass
  • Contrast: 7x10-4@0.3’’(100AU), 2x10-4@0.5’’(160AU), 6x10-5@1.0’’(320AU)
  • Corresponding 5σ detectable mass: 110 MJ, 80 MJ, 70 MJ
  • No further binary candidate was detected outer than 0.5’’
  • massive planets and brown dwarfs were not excluded at this point
  • Characterization of binary candidatesprojected separation: ~1000 AUBased on stellar SED (Table 3) in Kraus and Hillenbrand (2007).Assuming that the candidates are main sequence starsat the same distance as HAT-P-7.Step 2: Restricted region for Kozai migration
  • The timescale of Kozai migration in this system
  • PK,B ~ ~ 300 Myr
  • If a massive additional body with a shorter perturbation timescale exists, Kozai migration due to the binary cannot occur (Innanen et al. 1997, Wu and Murray 2003)
  • conditional equation:
  • (smaller bodies are allowed)
  • Allowed region for additional bodiesThe Kozai migration cannot occur if the timescale of orbital precession due to an additional body PG,c is shorter than that caused by Kozai mechanism PK,B (Innanen et al. 1997)Kozai migration forbiddenboundaryKozai migration allowedPossible additional planet ‘HAT-P-7c’Winn et al. (2009c)2008 and 2010 Subaru data2007 and 2009 Keck dataHJD - 2454000Long-term RV trend ~20 m/s/yr is ongoing from 2007 to 2010constraint on the mass and semi-major axis of ‘c’(Winn et al. 2009)Initial position of ‘c’In the presence of ‘c’the Kozai migration due to a binary star could not occur in this system!Step 3: Initial configuration for Kozai migration
  • If either of the candidates is a real binary, and no ‘c’ planet
  • By the angular momentum conservation (Kozai mechanism)
  • , : : semi-major axis and eccentricity of planet
  • : mutual inclination between orbital planes of planet and binary
  • 0: initial condition, n: now
  • necessary condition to initiate tidal evolution:
  • within 82.5 – 97.5 deg (even for the most optimistic case)
  • Summary for the HAT-P-7 case
  • We detected two binary candidates, and calculated restricted region for a possible additional body
  • Kozai migration was excluded in the presence of the additional body
  • We can constrain migration mechanisms for other systems by this procedure
  • Summary
  • RM measurements have discovered numbers of ‘tilted’ planets
  • tilted and/or eccentric planets are only explained by p-p scattering or Kozai migration
  • RM measurements cannot distinguish between p-p scattering and Kozai migration from spin-orbit alignment angles
  • Combination of direct imaging can resolve the problem
  • there are numbers of interesting targets to pinpoint a planetary migration mechanism
  • SEEDS can provide useful information for planetary migration
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