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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. transit in the Solar System.

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past and future studies of transiting extrasolar planets

Past and Future Studies of Transiting Extrasolar Planets

Norio Narita

National Astronomical Observatory of Japan

  • Introduction of transit photometry
  • Related studies for transiting planets
  • Future studies in this field
planetary transits
Planetary transits

transit in the Solar System

transit in exoplanetary systems

(we cannot spatially resolve)


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
The first exoplanetary transits

Charbonneau et al. (2000)

for HD209458b

transiting planets are increasing
Transiting planets are increasing

So far 58 transiting planets have been discovered.

gifts from transit light curve analysis

stellar radius, orbital inclination, mid-transit time

radius ratio

limb-darkening coefficients

planetary radius

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

planet radius

  • orbital inclination
  • planet mass
  • planet density
Additional observable parameters

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

by transit photometry.

what can we additionally learn
What can we additionally learn?
  • Additional Photometry
    • Secondary Eclipse
    • Transit Timing Variations
  • Additional Spectroscopy
    • Transmission Spectroscopy
    • The Rossiter-McLaughlin Effect
secondary eclipse

secondary eclipse

secondary eclipse

IRAC 8μm



Knutson et al. (2007)

Secondary Eclipse

provides ‘dayside’ thermal emission information

previous studies for hot jupiters
Previous studies for hot Jupiters
  • numbers of Spitzer detections
    • HD209458, TrES-1, HD189733, TrES-4, XO-1, etc
    • from the detections, we can estimate dayside temperature of these planets
recent studies
Recent studies
  • ground-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!

not constant!

Transit Timing Variations

constant transit timing

theoretical studies
Theoretical studies
  • Agol 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


Transmission Spectroscopy

A tiny part of starlight passes through planetary atmosphere.

theoretical studies for hot jupiters
Theoretical studies for hot Jupiters

Seager & Sasselov (2000)

Brown (2001)

Strong excess absorptions were predicted especially

in alkali metal lines and molecular bands

components discovered in optical

in transit

out of transit

Components discovered in optical
  • Sodium
    • HD209458b
      • Charbonneau et al. (2002) with HST/STIS
      • Snellen et al. (2008) with Subaru/HDS

Charbonneau et al. 2002

Snellen et al. 2008

components discovered in optical1
Components discovered in optical
  • Sodium
    • 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 nir
Components discovered in NIR
  • Vapor
    • HD209458b: Barman (2007)
    • HD189733b: Tinetti et al. (2007)
  • Methane
    • HD189733b: Swain et al. (2008)

▲:HST/NICMOS observation

red:model with methane+vapor

blue:model with only vapor

Swain et al. (2008)

other reports for atmospheres
Other reports for atmospheres
  • clouds
    • HD209458, HD189733
      • observed absorption levels are weaker than cloudless models
  • haze
    • HD189733
      • HST observation found nearly flat absorption feature around 500-1000nm → haze in upper atmosphere?

solid line:model


Pont et al. (2008)

transmission spectroscopy is useful to study planetary atmospheres

the rossiter mclaughlin effect
The Rossiter-McLaughlin effect

When a transiting planet hides stellar rotation,




hide approaching side

→ appear to be receding

hide receding side

→ appear to be approaching

radial velocity of the host star would have

an apparent anomaly during transit.

what can we learn from rm effect
What can we learn from RM effect?

The shape of RM effect

depends on the trajectory of the transiting planet.

well aligned


Gaudi & Winn (2007)

observable parameter
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)

previous studies
Previous studies
  • 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)
spin orbit misaligned exoplanet
Spin-orbit misaligned exoplanet

The RM effect of XO-3b

Winn et al. (2009)

(λ= 37.3 ± 3.7 degrees)

comparison with migration theories
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
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
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

The beginning of the Kepler era

from Kepler website

new telescopes for new targets
New telescopes for new targets

James Webb Space Telescope 


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

prospects for future studies
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
  • Transits enable us to characterize planets in details
  • Future studies for transiting Earth-like planets will be exciting!