Spin-Orbit Alignment Angles and

Planetary Migration of Jovian Exoplanets

Norio NaritaNational Astronomical Observatory of Japan

Outline

• Brief review of orbits of Solar System bodies

• Introduction of exoplanets and migration models

• How to measure spin-orbit alignment angles of

exoplanets

• Previous observations and results

• Summary and conclusions

Orbits of the Solar System Planets

All 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 proto-planetary disks

Orbits of Solar System Asteroids and SatellitesAsteroids

most of asteroids orbits in the ecliptic plane significant portion of asteroids have tilted orbits 24 retrograde asteroids have been discovered so far

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)These highly tilted or retrograde orbits are explained by

gravitational interaction with planets or Kozai mechanism

Motivation

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!

• First discovered in 1995, by Swiss astronomers (below)

• So far, over 400 candidates of exoplanets have been found

at 10th anniversary conferenceLeft: Didier Queloz Right: Michel Mayor

Introduction of Exoplanets

Semi-Major Axis Distribution of Exoplanets

Need planetary migration mechanisms!

Snow line

Jupiter

Standard Migration Models

consider gravitational interaction between

proto-planetary disk and planets

• 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

consider gravitational interaction between

planet-planet (planet-planet scattering models)

planet-binary companion (Kozai migration)

may be able to explain eccentricity distribution

e.g., Nagasawa+ 2008, Chatterjee+ 2008

predict a variety of eccentricities and also misalignments

between stellar-spin and planetary-orbital axes

ejected planet

Example of Misalignment Prediction

0 30 60 90 120 150 180 deg

Nagasawa, Ida, & Bessho (2008)

Misaligned and even retrograde planets are predicted.

How can we test these models by observations?

Planetary transits

2006/11/9transit 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 first exoplanetary transits

Charbonneau+ (2000)for HD209458b

Transiting planets are increasing

So far 62 transiting planets have been discovered.

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 the 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, Gimentz 2006, Gaudi & Winn 2007)

Note: orbital inclination

Sun’s equatorial plane

planetary orbital planeSun’s spin axis

Earth

planetary orbital plane

line of sight from the Earth

normal vector of line of sight

orbital inclinationin the Solar System

orbital inclinationin exoplanetary science

spin-orbit alignment anglein exoplanetary science

HD209458 Queloz+ 2000, Winn+ 2005 HD189733 Winn+ 2006 TrES-1 Narita+ 2007 HAT-P-2 Winn+ 2007, Loeillet+ 2008 HD149026 Wolf+ 2007 HD17156 Narita+ 2008,2009, Cochran+ 2008, Barbieri+

2009 TrES-2 Winn+ 2008 CoRoT-2 Bouchy+ 2008 XO-3 Hebrard+ 2008, Winn+ 2009 HAT-P-1 Johnson+ 2008 HD80606 Moutou+ 2009, Pont+ 2009, Winn+ 2009 WASP-14 Joshi+ 2008, Johnson+ 2009 HAT-P-7 Narita+ 2009, Winn+ 2009 WASP-17 Anderson+ 2009 CoRoT-1 Pont+ 2009 TrES-4 Narita+ to be submitted

Previous studiesRed: EccentricBlue: BinaryGreen: Both

Subaru Radial Velocity Observations

Iodine cell

HDS

Subaru

Prograde Planet: TrES-1bOur first observation with Subaru/HDS

Thanks to Subaru, clear detection of the Rossiter effect.

We confirmed a prograde orbit and

the spin-orbit alignment of the planet.

NN et al. (2007)

Aligned Ecctentric Planet: HD17156b

Well aligned in spite of its eccentricity.

Eccentric planet with the orbital period of 21.2 days.

NN et al. (2009a)λ = 10.0 ± 5.1 deg

Aligned Binary Planet: TrES-4b

NN et al. in prep.

Well aligned in spite of its binarity.

NN et al. in prep. λ = 5.3 ± 4.7 deg

Misaligned Eccentric Planet: XO-3b

Winn et al. (2009a)λ = 37.3 ± 3.7 deg

Hebrard et al. (2008)λ = 70 ± 15 deg

Misaligned Eccentric Planet: WASP-14b

Johnson et al. (2009)λ = -33.1 ± 7.4 deg

Misaligned Binary Planet: HD80606b

Winn et al. (2009b)λ = 53 (+34, -21)

deg

Pont et al. (2009)λ = 50 (+61, -36)

deg

Retrograde Exoplanet: HAT-P-7b

NN et al. (2009b)

Winn et al. (2009c)

Note: Implication of the results

Planetary systemseen from the Earth

We have not yet learnedthe inclination of the stellar spin axis

Earth

The planet is in a retrograde orbitwhen seen from the Earth

The true spin-orbit alignment angle will be determinedwhen the Kepler photometric data are available

(by asteroseismology)

Another Retrograde Exoplanet: WASP-17b

Anderson et al. (2009)

Summary of RM Studies

Exoplanets have a diversity in orbital distributions

We can measure spin-orbit alignment angles of exoplanets by

spectroscopic transit observations

4 out of 6 eccentric planets have highly tilted orbits

spin-orbit misalignments may be common for eccentric planets

2 out of 10 non-eccentric planets also show misaligned orbits

spin-orbit misalignements are rare for non-eccentric planets

we can add samples to learn a statistical population of

alinged/misaligned/retrograde planets (future task)

Conclusions and Future Prospects

Recent observations support planetary migration models

considering not only disk-planet interactions, but also planet-

planet scattering and the Kozai migration

The diversity of orbital distributions would be brought by the

various planetary migration mechanisms

We will be able to conduct similar studies for extrasolar

terrestrial planets in the future