Aligned, Tilted, Retrograde Exoplanets and their Migration Mechanisms Norio Narita (JSPS Fellow) National Astronomical Observatory of Japan

Aligned, Tilted, Retrograde Exoplanetsand their Migration Mechanisms

Norio Narita (JSPS Fellow)National Astronomical Observatory of Japan

I am a transit observer

“A transit of the Moon” observed

on July 22, 2009 at Hangzhou, China

I am a transit observer.

Photo by Norio Narita / Canon EOS Kiss X-2

I am working on

• Measurements of the Rossiter-McLaughlin effect for

transiting planetary systems

• High-contrast direct imaging for tilted or eccentric

(transiting) planetary systems

• Transmission spectroscopy for transiting planets to

detect exoplanetary atmospheres

• Measurements of transit timing variations of HAT-P-13b

Today’s talk

Outline

• Brief overview of orbits of Solar System bodies

• Orbits of exoplanets and their migration models

• The Rossiter-McLaughlin effect and observations


planetary systems

• Summary

Orbits of the Solar System Planets

Orbits of the Solar System Planets

All Solar System planets orbit in the same direction

small orbital eccentricities

At a maximum (Mercury) e = 0.2

small orbital inclinations

The spin axis of the Sun and the orbital axes of

planets are aligned within 7 degrees

In almost the same orbital plane (ecliptic plane)

The configuration is explained by core-accretion models

in a proto-planetary disk

Orbits of Jovian Satellites

Orbits of Solar System Asteroids and SatellitesAsteroids

most of asteroids orbits in the ecliptic plane significant portion of asteroids have tilted orbits dozens of retrograde asteroids have been discovered

Satellites orbital axes of satellites are mostly aligned with the

spin axis of host planets dozens of satellites have tilted orbits or even

retrograde orbits (e.g., Triton around Neptune)Tilted or retrograde orbits are common for those bodies

and are explained by scattering with other bodies etc

Motivation to study exoplanetary orbits

Orbits of the Solar System bodies reflect

the formation history of the Solar System

How about extrasolar planets?

Planetary orbits would provide us information

about formation histories of exoplanetary systems!

Outline





planetary systems

• Summary

Semi-Major Axis Distribution of Exoplanets

Need planetary migration mechanisms!

Snow line

Jupiter

Standard Migration Models

consider gravitational interaction between

proto-planets and proto-planetary disk

• Type I: less than 10 Earth mass proto-planets

• Type II: more massive case (Jovian planets)

well explain the semi-major axis distribution

e.g., a series of Ida & Lin papers

predict small eccentricities and small inclination for

migrated planets

Type I and II migration mechanisms

Eccentricity Distribution

Cannot be explained by Type I & II migration model

Jupiter

Eccentric Planets

Migration Models for Eccentric Planets


planet-planet (planet-planet scattering models)

planet-binary companion (Kozai migration)

ejected planet

captured planets

Kozai mechanism

companion

star

orbit 1: low eccentricity and high inclination

orbit 2: high eccentricity and low inclination

binary orbital plane

caused by perturbation from a distant companionand angular momentum conservation

originally for planet-satellite system (Kozai 1962)

Migration Models for Eccentric Planets


planet-planet (planet-planet scattering models)

planet-binary companion (Kozai migration)

may be able to explain the whole orbital distribution

e.g., Nagasawa+ 2008, Fabrycky & Tremaine 2007

predict a variety of eccentricities

and also predict misalignments between stellar-spin and

planetary-orbital axes

Examples of Obliquity PredictionTilted and even retrograde planets are predicted.

How can we test these models by observations?Morton & Johnson (2010)

Outline





planetary systems

• Summary

Planetary transits

2006/11/9

transit of Mercury

observed with Hinode

transit in the Solar System

If a planetary orbit passes in front of its host star by chance,

we can observe exoplanetary transits as periodical dimming.

transit in exoplanetary systems(we cannot spatially resolve)

slightly dimming

The Rossiter-McLaughlin effect

the planet hides the approaching side→ the star appears to be receding

the planet hides the receding side→ the star appears to be approaching

planet planetstar

When a transiting planet hides stellar rotation,

radial velocity of the host star would havean apparent anomaly during transits.

What can we learn from RM effect?

Gaudi & Winn (2007)

The shape of RM effectdepends on the trajectory of a transiting planet.

well aligned misaligned

Radial velocity during transits = the Keplerian motion and the RM effect

Observable parameter

λ ： sky-projected angle betweenthe stellar spin axis and the planetary orbital axis(e.g., Ohta+ 2005, Gaudi & Winn 2007, Hirano et al. 2010)

Subaru HDS Observations since 2006

Iodine cell

HDS

Subaru

HD17156b: Narita et al. (2009a) HAT-P-7b: Narita et al. (2009b)TrES-1b: Narita et al. (2007)

TrES-4b: Narita et al. (2010a)XO-4b: Narita et al. (2010c)

HAT-P-11b: Hirano et al. (2010b)

aligned alignedretrograde

aligned tilted

tilted

What we got

Discovery of Retrograde Orbit: HAT-P-7b

NN et al. (2009b)

Winn et al. (2009c)

Subaru observationthrough UH time

First RM Measurement forSuper-Neptune Planet ： HAT-P-11b

Hirano et al. (2010b)

Results of Previous Observations

Our group: Subaru telescope

13 targets observed

7 papers published and 3 papers are in prep.

5 out of 13 planets have tilted or retrograde orbit!

US: Keck telescope, UK, France: HARPS at 3.6m telescope

over 30 targets observed

similar percentage planets have tilted or retrograde orbit

now statistically assured

What we learned from RM measurements

Tilted or retrograde planets are not rare

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 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)

Outline





planetary systems

• Summary

Motivation for high-contrast direct imaging

The results of the RM effect encourage direct imaging because

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

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)

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

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

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

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…

speckle?

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 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)

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

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 I am working in a sub-category of known planetary systems, especially

targeting for tilted or eccentric planetary systems

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

AO188 limit

SCExAO limit

Remaining Problems

Correlation with properties of planet and host star

Need to observe more targets for statistics.

One cannot distinguish between p-p scattering and Kozai

migration for each system

Need to search for counterparts of migration processes

long term radial velocity measurements (< 10AU)

direct imaging (> 10-100 AU)

Documents

Aligned, Tilted, Retrograde Exoplanets and their Migration Mechanisms Norio Narita (JSPS Fellow) National Astronomical Observatory of Japan