Discriminating Migration Mechanisms ofTilted 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 ProblemsWhich 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 (> 10-100 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 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

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)

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. (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 - 2454000

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 mechanismStep 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 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

both Kozai and p-p scattering still survive

Future AO upgrade: SCExAO from 2011Subaru Coronagraphic Extreme-AO System

AO188 limit

SCExAO limit