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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
by radial velocity
spin-orbit alignment angle
by 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 discriminate
two 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
 Kozai migraion 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
binary
host star
planet
First 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 Images
N
NN et al. (2010)
E
Left: 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 bodies
H band contrast ratio
5σ detectable mass
 Contrast: [email protected]’’(100AU), [email protected]’’(160AU), [email protected]’’(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 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.
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 bodies
Kozai migration
forbidden
boundary
Kozai migration
allowed
The 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)
Possible additional planet ‘HAT-P-7c’
Winn et al. (2009c)
2007 and 2009 Keck data
2008 and 2010 Subaru data
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. 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