Norio Narita (NAOJ Fellow) Special Thanks to IRD Transit Team Members Search for New Transiting Exoplanets around Nearby Cool Dwarfs and their Characterization Norio Narita (NAOJ Fellow) Special Thanks to IRD Transit Team Members ©NAOJ

Outline Motivation for Searching Transiting Exoplanets around Nearby Cool Dwarfs Roadmap and Preparations for Discoveries High-Precision Near Infrared Photometry High-Precision Near Infrared Velocimetry Follow-up Studies Summary

Science Merits of Transiting Planets One can learn precise size of planets 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 of planets

Combined information provides 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

Year of Discovery Histogram (Transit) The number of transiting planets is rapidly growing.

Dedicated Space Mission for Transiting Planets CoRoT launched 2006/12/27 Kepler launched 2009/3/6

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

~50 candidates are in possible habitable zone. 5 are terrestrial size.

Kepler’s Weakness Kepler targets relatively faint and far stars Although over 2000 candidates discovered including possible habitable terrestrial planets, RV follow-ups for the targets are difficult Further characterization studies are also difficult Kepler is good for statistical studies, but not for detailed studies for each planet

Strategy of Future Transit Survey Future transit surveys will target nearby stars and aim to detect terrestrial planets in habitable zone Space-based all-sky transit survey for bright stars TESS (Transiting Exoplanet Survey Satellite) It is in the selection process of NASA Explore mission Ground-based transit survey for nearby cool dwarfs MEarth lead by D. Charbonneau at Harvard IRD transit group (collaborating with UH etc)

Science Merits of Transiting Planets around Nearby Cool (M-type) Dwarfs Good targets for searching transitng planets in HZ M dwarfs are cool and HZ of M dwarfs is relatively close-in Geometric transit probability becomes higher M dwarfs are small and thus transit depth becomes deeper M dwarfs are less massive and thus RV signal becomes larger Orbital period of planets in HZ is shorter Plenty of M dwarfs exist around the Solar System over 500 within 15 pc If detected, such planets are very interesting targets for further follow-up studies using IRD, TMT, SPICA etc

Difficulties of Cool Dwarfs Cool dwarfs are very faint in visible wavelength High precision photometry and velocimetry is difficult with current optical instruments (although a small part of targets are bright) But cool dwarfs are much brighter in near infrared wavelength 6>V-J>3 for M dwarfs, V-J>2 for late-K

Our Strategy We focus on high precision photometry and velocimetry in near infrared wavelength to search for transiting planets around nearby cool dwarfs Subaru will equip new IR Doppler instrument in near future (IRD: PI, Motohide Tamura) Subaru IRD aims to achieve ~1 m/s precision for J < 10 targets Our strategy Before IRD -> Transit Survey for J < 10 targets After IRD -> RV follow-up and further characterization studies

Ongoing Studies We have started high precision photometric follow-up of transiting planet candidates using 188 cm telescope at Okayama Astrophysical Observatory (OAO) ©NAOJ

Target Selection and Our Plan Based on SuperWASP (ground-based transit survey) archive data, transiting planet candidates around late-K or M dwarfs have been selected (about 50 candidates are observable from OAO) We aim to follow-up transiting planet candidates via high precision NIR photometry so as to eliminate false positives If confirmed, we plan to conduct RV measurements with current instruments (e.g., Subaru HDS) to confirm or refute its planetary nature by its mass

Okayama Proposal Accepted from 2011

Current Status of Transit Survey 6 clear nights among 19 allocated nights This is near average ratio of clear nights 4 targets have been observed 3 targets turned out to be false positives

Current Status of Transit Survey One candidate shows a transit-like dimming consistent with Rp/Rs ~ 0.042 ± 0.002 (~20σ detection)

Further Studies RV follow-up for discovered transiting planet candidates to determine their orbits and masses Transit follow-up for planets discovered by RV planet survey using IRD Further Studies for characterizing planets The Rossiter-McLaughlin effect Transmission spectroscopy / multi-band transit photometry Known planets and Kepler planet candidates around cool dwarfs (e.g., GJ1214b, KOI-254b) are also excellent targets

The Rossiter-McLaughlin Effect When a transiting planet hides stellar rotation, star planet planet the planet hides the approaching side → the star appears to be receding the planet hides the receding side → the star appears to be approaching radial velocity of the host star would have an apparent anomaly during transits. (cf. Teruyuki Hirano’s talk yesterday)

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

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

Useful Signs for Discriminating Models Super-earths around cool dwarfs are good targets NIR region multi-band (especially narrow-band) photometry IRSF/SIRIUS, OAO/ISLE etc are useful spectro-photometry is the most efficient Subaru/FMOS, MOIRCS are very useful Blue optical region detecting Rayreigh Scattering Subaru/Suprime-Cam is useful

Summary Searching for transiting planets around nearby cool dwarfs is one of the most important exoplanet studies we should start now We have started high precision photometric follow-up of transiting planet candidates at Okayama We aim to find transiting planets before commissioning of IRD and take an advantage of the Subaru IRD over other groups Stay tuned for new results!

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

cf. G3 V star vs M6 V star G3 V star M6 V star Rs ～ 1 Rsun ～ 0.005 AU Assuming Rp = 1 Earth radius ～ 0.01 Rsun Transit Probability： Rs/a ～ 0.5%, Transit Depth： (Rp/Rs)2 ～ 0.01% Transit Duration： Rs P / a π ～ 14hr, Orbital Period: P ～ 365 days M6 V star Rs ～ 0.1 Rsun ～ 0.0005 AU Typical HZ： a～0.005 AU、 P～10 hr Transit Probability： Rs/a ～ 10%, Transit Depth： (Rp/Rs)2 ～ 1% Transit Duration： Rs P / a π ～ 20 min