Transcript Document

Recent Developments of
Studies for Transiting Exoplanets
Norio Narita
National Astronomical Observatory of Japan
Outline
• Introduction of Science of Transiting Exoplanets
• What’s New and What’s Going on Now?
• Near Future Prospects
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
The first exoplanetary transits
Charbonneau+ (2000)
for HD209458b
Transiting planets are increasing
So far 69 transiting planets have been discovered.
Why are transits interesting?
We can characterize
origin, structure, and environment
of respective planets!
Scientific Subjects of Transits
Ongoing
• Mass-Size relation (structure)
• The Rossiter-McLaughlin effect (origin)
• Transmission Spectroscopy (environment)
• Secondary Eclipses (environment)
Near Future
• Transit Timing Variations
• Exo-Rings and Exo-Moons
Mass-Size Relation
(too inflated)
HAT-P-3 b
(heavy core)
TrES-4 b, etc
Charbonneau et al. (2006)
The Rossiter-McLaughlin effect
When a transiting planet hides stellar rotation,
star
planet
the planet hides
the approaching side
→ the star appears to
be receding
planet
the planet hides
the receding side
→ the star appears to
be approaching
radial velocity of the host star would have an apparent anomaly.
Transmission Spectroscopy
star
planet
stellar line
upper
atmosphere
dimming with
excess absorption
A tiny part of starlight passes through planetary atmosphere.
Secondary Eclipse
provide information of thermal emissions of the dayside
secondary
eclipse
secondary
eclipse
transit
IRAC 8μm
transit
Knutson et al. (2007)
Transit Timing Variations (TTV)
perturbing but not transiting planet (or exo-moon)
orbit of transiting planet
observer
observer
Exo-Rings and Exo-Moons
Taken by the Cassini spacecraft on September 15, 2006
(Credit: NASA/JPL/Space Science Institute)
Summary of Recent News
1. Discoveries of transiting super earths
2. Discoveries of highly tilted transiting planets
3. Kepler launched and recently announced results
4. Possible Transit Timing Variations?
5. Discovery of the largest Saturnian ring
1: Discoveries of Transiting Super Earths
and their Meanings
First Transiting Super Earth CoRoT-7b
CoRoT-7b: Rp=1.7 Rearth Mp=4.8 MEarth
CoRoT-7: K0V star, d = 150 pc
Leger et al. (2009), Queloz et al. (2009)
Second Discovery by MEarth Team
GJ1214b: Rp=2.68 REarth Mp=6.55 MEarth
GJ1214: M4.5V star, d = 13 pc
Charbonneau et al. (2009)
Previous Mass-Radius Relation
inflated !!
HAT-P-3
HD149026
Hartman et al. (2009)
Diversity of Jovian Planets
(too inflated)
HAT-P-3 b
(heavy core)
TrES-4 b, etc
Charbonneau et al. (2006)
New Mass-Radius Relation
Parameter space now
comes to Earth-like region
H+He
pure H2O
Diversity of Earth-like planets
H2O dominated
Earth-like
Charbonneau et al. (2009)
2: Discoveries of Highly Tilted Planets
and their Meanings
Do Such Planets Exist?
Stellar Spin
Planetary Orbit
Semi-Major Axis Distribution of Exoplanets
Snow line
Jupiter
Eccentricity Distribution
Eccentric
Planets
Jupiter
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
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
The Rossiter-McLaughlin effect
reflects the trajectory of planetary orbit in front of stellar surface
well aligned
misaligned
(tilted)
Radial velocity during transits = Keplerian motion + Rossiter effect
Gaudi & Winn (2007)
Previous studies of the RM effect
1.
HD209458
Queloz+ 2000, Winn+ 2005
2.
HD189733
Winn+ 2006
Red: Eccentric
3.
TrES-1
Narita+ 2007
4.
HAT-P-2
Winn+ 2007, Loeillet+ 2008
Blue: Binary
5.
HD149026
Wolf+ 2007
6.
HD17156
Narita+ 2008,2009, Cochran+ 2008, Barbieri+ 2009
7.
TrES-2
Winn+ 2008
8.
CoRoT-2
Bouchy+ 2008
9.
XO-3
Hebrard+ 2008, Winn+ 2009
10. HAT-P-1
Johnson+ 2008
11. HD80606
Moutou+ 2009, Pont+ 2009, Winn+ 2009
12. WASP-14
Joshi+ 2008, Johnson+ 2009
13. HAT-P-7
Narita+ 2009, Winn+ 2009
14. CoRoT-3
Triaud+ 2009
15. WASP-17
Anderson+ 2010
16. CoRoT-1
Pont+ 2010
17. WASP-3
Simpson+ 2010
18. Kepler-8
Jenkins+ 2010
19. TrES-4
Narita+ to be submitted
20. HAT-P-13
Winn+ to be submitted
Green: Both
Summary of RM Studies
 4 out of 7 eccentric planets have highly tilted orbits
 tilted planetary orbits may be common for eccentric planets
 3 out of 13 non-eccentric planets also show tilted orbits
 spin-orbit misalignements are rare for non-eccentric planets
 we can add samples to learn a statistical population of
alinged/misaligned/retrograde planets
 2 out of 20 transiting planets show retrograde orbits
 Distribution of spin-orbit alignment angles would be useful to
test planetary migration models
3: Kepler launched in 2009
and recently announced results
Beginning of the Kepler Era
Kepler launched on March 6, 2009
Just before the 5th Exoplanet Conference
in Kona
Kepler website
First result announced in August 2009
heat transfer
albedo
Kepler website
Kepler website
Kepler Started Exploration
• large number of Jovian, Neptunian, Earth-like
planets will be discovered
 Mass-Radius Distribution
 Spin-Orbit Alignment Distribution
 Albedo
 Heat Transfer
Many theoretical studies will be stimulated!
By the way…
Kepler can determine transit times of
transiting planets precisely.
What can we do with the Kepler data.
4: Observations of Transit Timing Variations
and Near Future Prospects
Transit Timing Variations (TTV)
perturbing but not transiting planet (or exo-moon)
orbit of transiting planet
observer
observer
Theoretical Studies
• For another planet:
– Agol et al. (2005) / Holman & Murray (2005)
– a few min for a hot Jupiter having an earth-mass planet in
2:1 resonance orbit
– If an earth-mass planet exists around a hot Jupiter, even
ground-based telescope would be able to detect TTV
• For exo-moon:
– Kipping 2009a, 2009b, Kipping et al. (2009)
– Exo-moons would be detectable with the Kepler
Likely First Discovery of TTV
O-C [min]
an Earth-mass planet in 4:1 resonant orbit?
1
0
-1
-2
case of no
TTV
266
366
Transit Epoch
446
Transit timing of OGLE-TR-111b (Diaz et al. 2008)
and TTV in this system is ongoing.
Kepler will discover numbers of additional
planets and exo-moons with TTV!
5: Discovery of the Largest Saturnian Ring
and Implication for Exo-Ring Exploration
Exo-Rings and Exo-Moons
Enceladus
Earth
Taken by the Cassini spacecraft on September 15, 2006
(Credit: NASA/JPL/Space Science Institute)
Methodology of Ring Detection
• Transit light curves for ringed
planets are slightly different
from those for no-ring planets
• Residuals between observed
light curves and theoretical
planetary light curves are ring
signals
• Signals are typically ~10-4 level
–
Detectable with HST/Kepler
• We can learn configuration of
rings with high precision
photometry
Barnes & Fortney (2004)
Discovery of the Largest Saturnian Ring
Largest ring extended
from 128 RSaturn to 207RSaturn
Verbiscer et al. (2009)
(Credit: NASA/JPL
Caltech/Keck)
If we observe the Saturn as a transiting planet,
differences of multiband transit light curves are quite large!
Characterization of Particle Size of Rings
• Diffractive forward-scattering
depends on ring’s particle size
and causes difference in
 depth of transit light curve
 ramp just before and after
transits
• Multi-wavelength observations
would be useful to characterize
distribution of particle size
• SPICA’s wide wavelength
coverage is useful to probe wide
variety of particle size
Barnes & Fortney (2004)
(for 0.5 micron observations)
Next Generation Telescopes
James Webb Space Telescope
after 2014
SPICA
after 2018
Thirty Meter Telescope
after 2018
Summary
Transit observations provide us
various interesting information to
characterize extrasolar planets!
Questions?