Past and Future Studies of

Transiting Extrasolar Planets

Norio Narita

National Astronomical Observatory of Japan

Outline

Introduction of transit photometry

Related studies for transiting

planets

Future studies in this field

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 et al. (2000)

for HD209458b

Transiting planets are increasing

So far 58 transiting planets have been discovered.

limb-darkening coefficients

planetary radius

radius ratio

stellar radius, orbital inclination, mid-transit time

Gifts from transit light curve analysis

Mandel & Agol (2002), Gimenez (2006), Ohta et al. (2009)

have provided analytic formula for transit light curves

Additional observable parameters

We can learn radius, mass, and density of transiting planets

by transit photometry.

planet radius

orbital inclination

planet mass

planet density

What can we additionally learn?

Additional Photometry

Secondary Eclipse

Transit Timing Variations

Additional Spectroscopy

Transmission Spectroscopy

The Rossiter-McLaughlin Effect

Secondary Eclipse

transit

secondary eclipse

Knutson et al. (2007)

transit

secondary eclipse

IRAC 8μm

provides ‘dayside’ thermal emission information

Previous studies for hot Jupitersnumbers of Spitzer detections

HD209458, TrES-1, HD189733, TrES-4, XO-1,

etc

from the detections, we can estimate dayside

temperature of these planets

Recent studiesground-based detections

Sing & Lopez-Morales (2009)• OGLE-TR-56, K-band, 8.2m VLT & 6.5m Magellan

• VLT: 0.037 ± 0.016 %, Magellan: 0.031 ± 0.011 %

de Mooij & Snellen (2009)• TrES-3, K-band, 3.6m ESO NTT / SOFI

• 0.241 ± 0.043 %

ground-based telescopes are able to

characterize dayside temperature of

exoplanets!

Transit Timing Variations

constant transit timing not constant!

Theoretical studiesAgol et al. (2005), Holman & Murray (2005)

additional planet causes modulation of TTVs

very sensitive to planets

• in mean-motion resonance

• in eccentric orbits

for example, Earth-mass planet in 2:1 resonance around a transiting hot Jupiter causes TTVs over a few min

ground-based observations (even with small telescopes) are useful to search for additional planets

in the Kepler era, TTVs will become one of an useful method to search for exoplanets

Transmission Spectroscopy

star

A tiny part of starlight passes through planetary atmosphere.

Seager & Sasselov (2000) Brown (2001)

Strong excess absorptions were predicted especially

in alkali metal lines and molecular bands

Theoretical studies for hot Jupiters

Components discovered in opticalSodium

HD209458b• Charbonneau et al. (2002) with HST/STIS

• Snellen et al. (2008) with Subaru/HDS

Charbonneau et al. 2002

in transit out of transit

Snellen et al. 2008

Components discovered in opticalSodium

HD189733b• Redfield et al. (2008) with HET/HRS

• to be confirmed with Subaru/HDS

Redfield et al. (2008) Narita et al. preliminary

Components discovered in NIRVapor

HD209458b: Barman (2007)

HD189733b: Tinetti et al. (2007)

MethaneHD189733b: Swain et al. (2008)

Swain et al. (2008)

▲： HST/NICMOS observation

red ： model with methane ＋vapor

blue ： model with only vapor

Other reports for atmospheres

Pont et al. (2008)

cloudsHD209458, HD189733

• observed absorption levels are weaker than cloudless models

hazeHD189733

• HST observation found nearly flat absorption feature around 500-1000nm → haze in upper atmosphere?

solid line ： model

■ ： observed

transmission spectroscopy is useful to study planetary atmospheres

The Rossiter-McLaughlin effect

hide approaching side→ appear to be receding

hide receding side→ appear to be

approaching

planet planetstar

When a transiting planet hides stellar rotation,

radial velocity of the host star would havean apparent anomaly during transit.

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

Observable parameter

λ ： sky-projected angle between

the stellar spin axis and the planetary orbital axis

(e.g., Ohta et al. 2005, Gimentz 2006, Gaudi & Winn 2007)

HD209458 Queloz et al. 2000, Winn et al. 2005

HD189733 Winn et al. 2006

TrES-1 Narita et al. 2007

HAT-P-2 Winn et al. 2007, Loeillet et al. 2008

HD149026 Wolf et al. 2007

HD17156 Narita+ 2008, Cochran+ 2008, Barbieri+ 2009

TrES-2 Winn et al. 2008

CoRoT-Exo-2 Bouchy et al. 2008

XO-3 Hebrard et al. 2008, Winn et al. 2009

HAT-P-1 Johnson et al. 2008

WASP-14 Joshi et al. 2008

(TrES-3, 4, WASP-1, 2, HAT-P-7, XO-2 Narita+. in prep)

Previous studies

Spin-orbit misaligned exoplanet

Winn et al. (2009)

(λ= 37.3 ± 3.7 degrees)

The RM effect of XO-3b

Comparison with migration theories

So far almost all planets show no large misalignment

consistent with standard Type II migration models

2 of 3 eccentric planets also show no misalignment

Only 1 exception is XO-3b

λ= 37.3 ± 3.7 degrees (Winn et al. 2009)

formed through planet-planet scattering?

The RM effect is useful to test planet migration models More samples (especially eccentric planets) needed

Summary of past studies

“Planetary transits” enable us to characterize

planetary size, inclination, and density

dayside temperature

clues for additional planets

components of atmosphere

obliquity of spin-orbit alignment

such info. is only available for transiting planets

Past studies were mainly done for hot Jupiters

from Kepler website

The beginning of the Kepler era

NASA Kepler mission

launched last week!

Large numbers of transiting

planets will be discovered

Hopefully Earth-like planets

in habitable zone may be

discovered

Future studies will target

such new planets

New telescopes for new targets

James Webb Space Telescope  SPICA

We will be able to observe transits and secondary eclipses of new targets with these new telescopes.

Prospects for future studies

Future studies include characterization of new

transiting planets with new telescopes

many Jovian planets, super Earths, and smaller planets

rings, moons will be searched around transiting planets

secondary eclipse observations to measure dayside

temperature

transmission spectroscopy for Earth-like planets in

habitable zone to search for biomarkers

Summary

Transits enable us to characterize planets in

details

Future studies for transiting Earth-like planets will

be exciting!