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Further Science of IRD:
Synergy with Transiting Planets
Norio Narita (NAOJ)
Thanks to IRD Transit Group
Members of the IRD Transit Group
• Norio Narita (Chief: NAOJ)
• Akihiko Fukui (NAOJ, Okayama Astrophysical Obs.)
• Teruyuki Hirano (Univ. of Tokyo)
• Takuya Suenaga (NAOJ, Sokendai)
• Yasuhiro Takahashi (Univ. of Tokyo)
• Hiroshi Ohnuki (Tokyo Institute of Technology)
Outline
• Brief Introduction of Transiting Planets
• Searching Transiting Planets with IRD
– Transit Follow-up of RV-detected Planets
– Transit Survey and RV Follow-up
• Further Sciences for Transiting Planets
– Probing Mass-Radius Relation of Small Planets
– Probing Atmospheres
– Probing Formation/Migration History
• Summary
What is Planetary Transits?
A phenomenon that a planet passes across in front of its host star
Venus transit @ Maui, 2012
Same can happen in
exoplanetary systems
slightly dimming
What we can learn from transit light curve
stellar radius, orbital inclination, mid-transit time
ratio of
planet/star size
planet radius
stellar limb-darkening
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
Other Merits of Transiting Planets
• Also, transit observations enable us to infer
– internal structure of planets
– atmospheric composition of planets
– orbital migration history of planets
How to Find Transiting Exoplanets
• RV survey and transit follow-up
– HD209458b, HD149026b…
– GJ436b, GJ3470b
• Transit survey and RV follow-up
– HAT, WASP, CoRoT, Kepler
– GJ1214b, KOI-961b,c,d (=Kepler-42)
The First Discovery of a Transiting Planet
RVs can predict possible transit times
Mazeh et al. (2000)
Charbonneau et al. (2000)
RVs of HD209458b
Transits of HD209458b
How often does it happen?
Some Characteristics of Transiting Planets
stellar radius：
semi-major axis：
planetary radius :
Toward Earth
orbital period：
Transit Probability：
～ Rs/a
Transit Depth：
～ (Rp/Rs)2
Transit Duration：
～ Rs P/a π
Transit Probabilities for IRD Targets
• IRD main targets are M dwarfs
• Bonfils et al. (2011) reported results of HARPS RV
survey for M dwarfs that super-Earths are frequent
– P = 1-10days : f=0.36 (+0.25, -0.10)
– P = 10-100days : f=0.35 (+0.45, -0.11)
– If IRD monitor ~200 M dwarfs, IRD can find ~70 super-
Earths
Transit Probabilities for M0V & M6V
• M0V
– Rs ～ 0.62 Rsun ～ 0.00288 AU
– P = 100 days -> a ～ 0.334 AU, Transit Probability： Rs/a ～ 0.86%
– P = 10 days -> a ～ 0.072 AU, Transit Probability： Rs/a ～ 4%
– P = 1 days -> a ～ 0.0155 AU, Transit Probability： Rs/a ～ 18.5%
• M6V
– Rs ～ 0.1 Rsun ～ 0.000465 AU
– P = 10 days -> a ～ 0.195 AU, Transit Probability： Rs/a ～ 0.24%
– P = 10 days -> a ～ 0.042 AU, Transit Probability： Rs/a ～ 1.66%
– P = 1 days -> a ～ 0.009 AU, Transit Probability： Rs/a ～ 7.75%
Expected Number of Transiting Planets
• Transit probability for P = 100 days is very low
• For P = 1-10 days, probability is not bad (1.66-18.5%)
– IRD aims detections of ~70 planets by RV method
– If 70 super-Earths at P = 1-10 days are discovered around
M dwarfs, there would be several (1-13) transiting planets
– Importantly, planets with P = 1-10 days can be habitable
around M5-6-type dwarfs
Can we follow-up such transiting planets?
• Answer is YES!
• IRD targets are typically J < 10
• Transiting super-Earths (even Earth size) around M
dwarfs cause typically over 1mmag dimming
• If we can achieve 1mmag sensitivity for J < 10 targets,
we can detect such transits
– We have prepared such high precision transit photometry
Example at Okayama, Japan (J band)
~1mmag is achieved for J~10 target (Fukui et al. in prep.)
Example at IRSF, South Africa (JHKs bands)
GJ1214b transit in JHKs bands in 2011
~1mmag is achieved for J~10 target (Narita et al. submitted)
With those telescopes, we plan to follow-up all IRD detected planets.
Transit Survey and RV Follow-up Strategy
• We have started a collaboration with an UH group (Eric
Gaidos, Andrew Mann, et al.)
– They have prepared a transiting planet candidate catalog
based on the WASP archive data and they are preparing a new
all-sky nearby M dwarf catalog
• Based on the transiting planet candidate catalog, we have
started transit confirmation observations using 188 cm
telescope at Okayama Astrophysical Observatory from 2011
Okayama Proposal Accepted
Ongoing Studies
• We selected about 50 candidates from the catalog
– The targets are middel-K – early M dwarfs
– We aim to follow-up transiting planet candidates via high
precision NIR photometry so as to eliminate false positives
– false positive rate would be as high as ~90%
• We will follow-up all the candidates before IRD runs
– We are awarded 23 nights in 2012B semester
– We expect a few good candidates for RV confirmation with IRD
Summary of Transiting Planet Search
• If IRD RV survey can find ~70 planets around M dwarfs, we
expect to find several transiting planets from transit follow-up
• From our ongoing transit survey, we expect to find a few
transiting planets for IRD RV follow-up
• Known transiting planets around M dwarfs with J < 10
– only 3 (GJ436, GJ1214, GJ3470)
• IRD + transit observations are quite important to add the
number of transiting planets around M dwarfs!
Further Sciences
• Transiting planets allow us to probe
– internal structure of planets
– atmospheric composition of planets
– orbital migration history of planets
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 (rocky)
Charbonneau et al. (2009)
Mass-Radius Relation for “Super-Earths”
Courtesy of M. Ikoma
There is a wide diversity of
internal structure of
super-Earths.
Theoretical models can predict
mass-radius relation for a variety
of bulk compositions, but models
are often degenerated.
How can we discriminate
compositions?
Transit Spectroscopy / Band Photometry
star
Transit depth depends on wavelength
Case for GJ1214b
de Mooij et al. (2011)
Green: H2 dominated with solar metallicity
Red: H2 dominated with sub-solar metallicity and cloud layer at 0.5 bar
Blue: Vapor dominated atmosphere
Our group also works on GJ1214b
Up: GJ1214b transit in JHKs bands with
IRSF/SIRIUS (NN+ submitted)
Left: GJ1214b transit in B band with
Subaru/Suprime-Cam (NN+ in prep.)
Inferring Formation History of Planetary Systems
scattering
captured planets
©Newton Press
ejected planet
Recent Understanding of Planet Migration
Stellar Spin
Planetary
Orbit
As for hot Jovian planets, tilted orbits are not so rare.
--> Various migration mechanisms indeed occur in the universe.
The Rossiter-McLaughlin effect
When a transiting planet hides stellar rotation,
star
planet
planet
the planet hides the approaching side
the planet hides the receding side
→ the star appears to be receding
→ the star appears to be approaching
radial velocity of the host star would have
an apparent anomaly during transits.
On Formation History of M Dwarf Planets
Are there any tilted or retrograde super-Earths?
λ： sky-projected angle between
the stellar spin axis and the planetary orbital axis
(e.g., Ohta et al. 2005, Gaudi & Winn 2007, Hirano et al. 2010)
Merit of IRD for the RM study
• M dwarfs are very faint in visible wavelength
• Measurements of the RM effect need enough time-resolution
and RV-precision
• Actually, GJ436 (V=10.6, J=6.9), GJ1214 (V=14.7, J=9.8),
GJ3470 (V=12.3, J=8.8) are quite difficult targets with the
current visible instruments -> IRD can significantly improve
time-resolution and enable us to determine λ for those
planets
Conclusion
• IRD will find transiting planets around M dwarfs
• The discovered planets will give us further detailed
studies on their planetary nature