Search for New Transiting Exoplanets around Nearby Cool Dwarfs and their Characterization Norio...
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![Page 1: Search for New Transiting Exoplanets around Nearby Cool Dwarfs and their Characterization Norio Narita (NAOJ Fellow) Special Thanks to IRD Transit Team.](https://reader036.fdocuments.net/reader036/viewer/2022062518/56649de55503460f94add39f/html5/thumbnails/1.jpg)
Search for New Transiting Exoplanets around Nearby Cool Dwarfs and their Characterization
Norio Narita (NAOJ Fellow)Special Thanks to IRD Transit Team Members ©NAOJ
![Page 2: Search for New Transiting Exoplanets around Nearby Cool Dwarfs and their Characterization Norio Narita (NAOJ Fellow) Special Thanks to IRD Transit Team.](https://reader036.fdocuments.net/reader036/viewer/2022062518/56649de55503460f94add39f/html5/thumbnails/2.jpg)
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
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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
![Page 4: Search for New Transiting Exoplanets around Nearby Cool Dwarfs and their Characterization Norio Narita (NAOJ Fellow) Special Thanks to IRD Transit Team.](https://reader036.fdocuments.net/reader036/viewer/2022062518/56649de55503460f94add39f/html5/thumbnails/4.jpg)
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
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Year of Discovery Histogram (Transit)
The number of transiting planets is rapidly growing.
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Dedicated Space Mission for Transiting Planets
CoRoTlaunched 2006/12/27
Keplerlaunched 2009/3/6
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<1.25 RE
First 4 Month Kepler Planet Candidates
1235 Planet Candidates
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~50 candidates are in
possible habitable zone.
5 are terrestrial size.
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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
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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)
![Page 12: Search for New Transiting Exoplanets around Nearby Cool Dwarfs and their Characterization Norio Narita (NAOJ Fellow) Special Thanks to IRD Transit Team.](https://reader036.fdocuments.net/reader036/viewer/2022062518/56649de55503460f94add39f/html5/thumbnails/12.jpg)
Science Merits of Transiting Planetsaround 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
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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
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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
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Ongoing Studies• We have started high precision photometric follow-up of
transiting planet candidates using 188 cm telescope at Okayama Astrophysical Observatory (OAO)
©NAOJ
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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
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Okayama Proposal Accepted from 2011
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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
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Current Status of Transit Survey
One candidate shows a transit-like dimming consistent withRp/Rs ~ 0.042 ± 0.002 (~20σ detection)
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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
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The Rossiter-McLaughlin Effect
the planet hides the approaching side→ the star appears to be receding
the planet hides the receding side→ the star appears to be approaching
planet planetstar
When a transiting planet hides stellar rotation,
radial velocity of the host star would havean apparent anomaly during transits.
(cf. Teruyuki Hirano’s talk yesterday)
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Transit Spectroscopy / Band Photometry
star
Transit depth depends on lines or bands.
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Inferring Atmospheric Composition of GJ1214b
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
de Mooij et al. (2011)
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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
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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!
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