Post on 04-Jan-2016
Discriminating Planetary Migration Mechanisms
by Direct Imaging
Norio NaritaNational Astronomical Observatory of Japan
on behalf of SEEDS/HiCIAO/AO188 teams
Clues to discriminate migration models
small eccentricity and obliquitydisk-planet interaction
large eccentricity or obliquityplanet-planet scattering
Kozai migration
orbital eccentricityby radial velocity
spin-orbit alignment angleby the RM effect
Can we discriminate two models?
• Planet-Planet scattering
• Kozai migration
Additional information from direct imaging!
We introduce a procedure to discriminatetwo planetary migration models by direct imaging.
SEEDS ProjectSEEDS: 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
planet
binary
host star
First Application: HAT-P-7
not eccentric, but misaligned (NN+ 2009, Winn et al. 2009)
very interesting target for direct imaging observation!
NN et al. (2009) Winn et al. (2009)
Step 1: Direct Imaging ObservationsSubaru/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
ENN et al. (2010)
Constraints on other outer bodies
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
H band contrast ratio 5σ detectable mass
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
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
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)Kozai migration
allowed
boundary
Kozai migration forbidden
Possible additional planet ‘HAT-P-7c’
HJD - 2454000
Winn et al. (2009c) 2008 and 2010 Subaru data2007 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. 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