spin-orbit alignment angles and planetary migration of jovian exoplanets norio narita national...
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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 conference
Left: 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
2006/11/9
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 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: Eccentric
Blue: Binary
Green: 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