Discriminating Planetary Migration Mechanismsby 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