Download Jupiter Eccentric Planets

Spin-Orbit Alignment Angles and
Planetary Migration of Jovian Exoplanets
Norio Narita
National 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 Satellites
 Asteroids
 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!
Introduction of Exoplanets
• First discovered in 1995, by Swiss astronomers (below)
• So far, over 400 candidates of exoplanets have been found
at 10th anniversary conference
Left: Didier Queloz Right: Michel Mayor
Semi-Major Axis Distribution of Exoplanets
Snow line
Jupiter
Need planetary migration mechanisms!
Standard Migration Models
Type I and II migration mechanisms
 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
Eccentricity Distribution
Eccentric
Planets
Jupiter
Cannot be explained by Type I & II migration model
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
Misaligned and even retrograde planets are predicted.
0
30
60
90
120
150
180 deg
Nagasawa, Ida, & Bessho (2008)
How can we test these models by observations?
Planetary transits
transit in the Solar System
transit in exoplanetary systems
(we cannot spatially resolve)
2006/11/9
transit of Mercury
observed with Hinode
slightly dimming
If a planetary orbit passes in front of its host star by chance,
we can observe exoplanetary transits as periodical 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
When a transiting planet hides stellar rotation,
star
planet
planet
the planet hides the approaching side
the planet hides the receding side
→ the star appears to be receding
→ the star appears to be approaching
radial velocity of the host star would have
an apparent anomaly during transits.
What can we learn from RM effect?
The shape of RM effect
depends on the trajectory of the transiting planet.
well aligned
misaligned
Radial velocity during transits = the Keplerian motion and the RM effect
Gaudi & Winn (2007)
Observable parameter
λ： sky-projected angle between
the stellar spin axis and the planetary orbital axis
(e.g., Ohta+ 2005, Gimentz 2006, Gaudi & Winn 2007)
Note: orbital inclination
Sun’s spin axis
planetary orbital plane
Sun’s equatorial plane
orbital inclination
in the Solar System
spin-orbit alignment angle
in exoplanetary science
normal vector of line of sight
planetary orbital plane
line of sight from the Earth
orbital inclination
Earth in exoplanetary science
Previous studies
Red: Eccentric
 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
Blue: Binary
Green: Both
Subaru Radial Velocity Observations
HDS
Subaru
Iodine cell
Prograde Planet: TrES-1b
Our first observation with Subaru/HDS
NN et al. (2007)
Thanks to Subaru, clear detection of the Rossiter effect.
We confirmed a prograde orbit and
the spin-orbit alignment of the planet.
Aligned Ecctentric Planet: HD17156b
Eccentric planet with the
orbital period of 21.2 days.
NN et al. (2009a)
λ = 10.0 ± 5.1 deg
Well aligned in spite of its eccentricity.
Aligned Binary Planet: TrES-4b
NN et al. in prep. λ = 5.3 ± 4.7 deg
NN et al. in prep.
Well aligned in spite of its binarity.
Misaligned Eccentric Planet: XO-3b
Hebrard et al. (2008)
λ = 70 ± 15 deg
Winn et al. (2009a)
λ = 37.3 ± 3.7 deg
Misaligned Eccentric Planet: WASP-14b
Johnson et al. (2009)
λ = -33.1 ± 7.4 deg
Misaligned Binary Planet: HD80606b
Pont et al. (2009)
λ = 50 (+61, -36) deg
Winn et al. (2009b)
λ = 53 (+34, -21) deg
Retrograde Exoplanet: HAT-P-7b
NN et al. (2009b)
Winn et al. (2009c)
Note: Implication of the results
The planet is in a retrograde orbit
when seen from the Earth
Earth
Planetary system
seen from the Earth
We have not yet learned
the inclination of the stellar spin axis
The true spin-orbit alignment angle will be determined
when 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 planetplanet 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