Photometric Studies of Transiting Exoplanets

1. Photometric Studies of Transiting Exoplanets Norio Narita (NAOJ) Transit of Venus on June 5, 2012 at Hawaii

2. Outline • Introduction of Transit • Current Status of Studiesof Transiting Exoplanets • Further Studies of Transiting Exoplanets • How to Observe Transits by Youeself? • Summary

3. What is Transit? secondary eclipse planetary orbit primary eclipse = transit

4. How to Find Transiting Exoplanets • We cannot spatially resolve a transiting exoplanet, but we can observe slight dimming due to transits Methods to search for transiting exoplanets • Photometric follow-up of RV known planets • Transit survey and RV follow-up

5. The First Discovery of a Transiting Exoplanet Charbonneau et al. (2000) Transits of “hot Jupiter” HD209458b (Possible transit times were predicted by RV)

6. Transit Survey One can search for periodic dimming from this kind of data

7. Some Characteristics of Transiting Planets planetary radius : stellar radius： semi-major axis： Toward Earth orbital period： Transit Probability： Transit Depth： Transit Duration： ～ Rs/a ～ (Rp/Rs)2 ～ RsP/a π

8. Science Importance of Transiting Planets • One can learn precise size of planets • One can also learn true mass and density of planets when combined with RV • The information is only available for transiting planets • Also, transit observations enable us to infer • internal structure of planets • atmospheric composition of planets • orbital migration history (Talk by Hirano tomorrow)

9. What we can learn from transit light curve stellar radius, orbital inclination, mid-transit time ratio of planet/star size stellar limb-darkening planet radius Analytic transit light curve was modeled by Mandel & Agol (2002)

10. When combined with RVs • RVs provide • minimum mass: Mp sin i • Transits provide • planetary radius: Rp • orbital inclination: i • Combined information provides • planetary mass: Mp • planetary density: ρ

11. Inferring Internal Structure of Planets Solid line: H/He dominated Dashed line: 100% H2O Dotted line: 75% H2O, 22% Si, 3% Fe core Dot-dashed line: Earth-like Transits revealed varieties of planets’ structure Charbonneauet al. (2009)

12. Transit Spectroscopy / Band Photometry star Transit depth depends on lines or bands

13. Inferring Atmospheric Composition of GJ1214b de Mooijet al. (2011) Green: H dominated with solar metallicity Red: H dominated with sub-solar metallicity and cloud layer at 0.5 bar Blue: Vapor dominated atmosphere

14. Current Status of Studies of Transiting Exoplanets The number of transiting planets is rapidly growing.

15. Dedicated Space Mission for Transiting Planets Kepler launched2009/3/6 CoRoT launched 2006/12/27

16. Kepler Field of View

17. Pre-Kepler Transiting Planets HAT-P-11 (Kepler-3) HAT-P-7 (Kepler-2) TrES-2 (Kepler-1)

18. First 4 Month Kepler Planet Candidates <1.25 RE 1235 Planet Candidates

19. 2326 Planet Candidates

20. 54 candidates are in possible habitable zone. 5 are terrestrial size.

21. Possible Habitable Planet Kepler-22b

22. (Sub-)Earth-sized Planets Earth-sized planet Kepler-20f Mars-sized planet KOI-961.03 (renamed as Kepler-42d)

23. Now Not a Science Fiction Planetary Systems with Two Suns: Kepler-16, 34, 35, 47 →　Tatooine-like (in Star Wars) planet

24. Summary of Current Status • Various transiting exoplanets have been discovered • hot Jupiters • hot Nuptunes • super Earths • habitable planets • Tatooine-like planets • We have learned that there are various interesting transiting exoplanets • What’s next?

25. Kepler’s Weakness • Kepler targets relatively faint and far stars • Although over 1000 candidates discovered, RV follow-ups for all targets are difficult • Further characterization studies are also difficult • Kepler is good for statistical studies, but not for detailed studies for each planet

26. Strategy of Future Transit Survey • Future transit surveys will target nearby bright stars to detect terrestrial planets in habitable zone • Space-based all-sky transit survey for bright stars • TESS (Transiting Exoplanet Survey Satellite) by MIT team • Ground-based transit survey for nearby M dwarfs • MEarth lead by D. Charbonneau at Harvard • Other teams all over the world • Our IRD transit group (collaborating with UH etc)

27. What we would like to do • To search for new interesting transiting planets orbiting nearby bright stars • To characterize nature (internal structure, atmosphere, habitability) of those planets • To do so, we need to observe transiting exoplanets with high precision!

28. How to Observe Transits by Yourself • First you need to get observing time at your university or openuse facilities • not necessarily large telescope for bright targets • Let’s try submitting a proposal • You can find information of transiting planets and transit ephemeris at • http://exoplanet.eu/catalog/(Exoplanet.eu) • http://var2.astro.cz/ETD/ (Exoplanet Transit Database)

29. How to Achieve High Precision Transit Photometry • High precision (~0.1% or ~1mmag) photometry was considered to be very difficult previously • A good solution is • to fix stellar position on the detector during observations • with image defocus

30. Example of Detector Image Field of View ~20 pix diameter Stars are defocused and kept off from bad pixels.

31. Example at Okayama in Japan (J band) ~1mmag is achieved for J~10 target (Fukui et al. in prep.)

32. Example at Okayama (Ks band) ~1mmag is achieved for Ks~10 target (Ohnuki et al. in prep.)

33. Example at South Africa / IRSF ~1 mmag is achieved for J < 10 target (Narita et al. 2013)

34. Example at Subaru Suprime-Cam (B band) 0.8 mmag is achieved for B = 16.4 target! (Narita et al. in prep.)

35. Let’s try transit observations • Using the simple technique, we can observe exoplanetary transits with high precision • to fix stellar position on the detector during observations • with image defocus • If you are interested, you can submit a proposal in your country or other countries’ openuse time!

36. Summary • Transits provide us useful information for properties of exoplanets • Numbers of interesting transiting exoplanets have been discovered • With the simple technique, you can achieve good precision for transit photometry • So please try transit photometry by yourself!