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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. 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

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  1. Past and Future Studies of Transiting Extrasolar Planets Norio Narita National Astronomical Observatory of Japan

  2. Outline • Introduction of transit photometry • Related studies for transiting planets • Future studies in this field

  3. 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 If a planetary orbit passes in front of its host star by chance, we can observe exoplanetary transits as periodical dimming.

  4. The first exoplanetary transits Charbonneau et al. (2000) for HD209458b

  5. Transiting planets are increasing So far 58 transiting planets have been discovered.

  6. 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

  7. planet radius • orbital inclination • planet mass • planet density Additional observable parameters We can learn radius, mass, and density of transiting planets by transit photometry.

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

  9. secondary eclipse secondary eclipse IRAC 8μm transit transit Knutson et al. (2007) Secondary Eclipse provides ‘dayside’ thermal emission information

  10. 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

  11. 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!

  12. not constant! Transit Timing Variations constant transit timing

  13. 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

  14. star Transmission Spectroscopy A tiny part of starlight passes through planetary atmosphere.

  15. Theoretical studies for hot Jupiters Seager & Sasselov (2000) Brown (2001) Strong excess absorptions were predicted especially in alkali metal lines and molecular bands

  16. 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

  17. 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

  18. 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)

  19. 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 ■：observed Pont et al. (2008) transmission spectroscopy is useful to study planetary atmospheres

  20. The Rossiter-McLaughlin effect When a transiting planet hides stellar rotation, star planet planet 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.

  21. What can we learn from RM effect? The shape of RM effect depends on the trajectory of the transiting planet. well aligned misaligned Gaudi & Winn (2007)

  22. 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)

  23. 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)

  24. Spin-orbit misaligned exoplanet The RM effect of XO-3b Winn et al. (2009) (λ= 37.3 ± 3.7 degrees)

  25. 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

  26. 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

  27. 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

  28. 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.

  29. 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

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

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