recent developments of studies for transiting exoplanets

Recent Developments of

Studies for Transiting Exoplanets

Norio NaritaNational 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

2006/11/9transit of Mercury

observed with Hinode

transit in the Solar System transit in exoplanetary systems(we cannot spatially resolve)

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 TransitsOngoing• 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

Charbonneau et al. (2006)

(too inflated)

HAT-P-3 b(heavy core)

TrES-4 b, etc

The Rossiter-McLaughlin effect

the planet hidesthe approaching side→ the star appears to

be receding

the planet hidesthe receding side

→ the star appears tobe approaching

planet planetstar

When a transiting planet hides stellar rotation,

radial velocity of the host star would have an apparent anomaly.

Transmission Spectroscopy

stellar linedimming with

excess absorption

upperatmosphere

planet

star

A tiny part of starlight passes through planetary atmosphere.

Secondary Eclipse

transit

secondary eclipse

Knutson et al. (2007)

transit

secondary eclipse

IRAC 8μm

provide information of thermal emissions of the dayside

Transit Timing Variations (TTV)perturbing but not transiting planet (or exo-moon)

orbit of transiting planetobserver 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 pcLeger 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 pcCharbonneau et al. (2009)

Previous Mass-Radius Relation

Hartman et al. (2009)

inflated !!

HD149026

HAT-P-3

Diversity of Jovian Planets

Charbonneau et al. (2006)

(too inflated)

HAT-P-3 b(heavy core)

TrES-4 b, etc

New Mass-Radius Relation

Charbonneau et al. (2009)

Parameter space now comes to Earth-like region

H+He

pure H2O

H2O dominatedEarth-like

Diversity of Earth-like planets

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

Jupiter

Eccentric Planets

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

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 effectreflects 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)

1. HD209458 Queloz+ 2000, Winn+ 20052. HD189733 Winn+ 20063. TrES-1 Narita+ 20074. HAT-P-2 Winn+ 2007, Loeillet+ 20085. HD149026 Wolf+ 20076. HD17156 Narita+ 2008,2009, Cochran+ 2008, Barbieri+ 20097. TrES-2 Winn+ 20088. CoRoT-2 Bouchy+ 20089. XO-3 Hebrard+ 2008, Winn+ 200910. HAT-P-1 Johnson+ 200811. HD80606 Moutou+ 2009, Pont+ 2009, Winn+ 200912. WASP-14 Joshi+ 2008, Johnson+ 200913. HAT-P-7 Narita+ 2009, Winn+ 200914. CoRoT-3 Triaud+ 200915. WASP-17 Anderson+ 201016. CoRoT-1 Pont+ 201017. WASP-3 Simpson+ 201018. Kepler-8 Jenkins+ 201019. TrES-4 Narita+ to be submitted20. HAT-P-13 Winn+ to be submitted

Previous studies of the RM effectRed: EccentricBlue: BinaryGreen: 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

Kepler website

albedo

heat transfer

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 planetobserver 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

Transit Epoch

01

-1-2

266 366 446

O-C

[m

in]

case of no TTV

Transit timing of OGLE-TR-111b (Diaz et al. 2008)

and TTV in this system is ongoing.

an Earth-mass planet in 4:1 resonant orbit?

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

Taken by the Cassini spacecraft on September 15, 2006(Credit: NASA/JPL/Space Science Institute)

Enceladus Earth

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 photometryBarnes & Fortney (2004)

Discovery of the Largest Saturnian Ring

Verbiscer et al. (2009)(Credit: NASA/JPL

Caltech/Keck)

Largest ring extended

from 128 RSaturn to 207RSaturn

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 TelescopesJames Webb Space Telescope  SPICA

after 2014  after 2018 

Thirty Meter Telescope  after 2018

Summary

Transit observations provide us

various interesting information to

characterize extrasolar planets!

Questions?