1. 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

2. 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

3. 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

4. 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

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

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

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

9. ~50 candidates are in possible habitable zone.
5 are terrestrial size.

10. 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

11. 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)

12. 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

13. 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

14. 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

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

16. 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

17. Okayama Proposal Accepted from 2011

18. 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

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

20. 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

21. 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)

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

23. 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

24. 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

25. 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!

27. 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

28. 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 ～ 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