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Transiting Exoplanet Search and Characterization with
Subaru's New Infrared Doppler Instrument (IRD)
Norio Narita (NAOJ)
On behalf of IRD Transit Group
Outline of This Talk
1. Searching new transiting planets around cool host
stars before and after IRD’s first light
2. Characterizing new transiting planets with IRD and
other telescopes / instruments
How to Find Transiting Exoplanets
• RV detection and transit follow-up
– HD209458b, HD189733b, HD149026b…
– GJ436b, GJ3470b…
– How many transiting planets can be discovered with IRD?
• Transit survey and RV follow-up
– TrES, HAT, WASP, XO, CoRoT, Kepler, MEarth…
– GJ1214b, Kepler planets
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’s 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 = 100 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 IRD Transiting Planets
• Transit probability for P = 100 days is too low
• For P = 1-10 days, probability is not bad (several %)
– 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 a few new transiting planets
• Planets with P = 1-10 days can be habitable around
M5-6-type dwarfs
Ongoing/Future Transit Surveys around M Dwarfs
• Transit surveys before IRD’s first light
– MEarth (Harvard) and other teams in the world
– SEAWOLF survey (UH/NAOJ/etc)
– MOA-II transit survey (NAOJ/MOA)
• Future Space-based Survey with IRD follow-up
– TESS from 2017 (MIT/NASA)
SEAWOLF Survey
• Transit survey using Super-WASP
archive data and Lepine & Gaidos
M dwarf catalog
• High precision transit follow-up by
northern hemisphere telescopes
• IRD transit group used Okayama
1.88m telescope in Japan
• Unfortunately no detection, but
constrain the occurrence rate of
hot Neptunes around late-K & M
stars as 5.3 ± 4.4 % (Gaidos+
2013)
target distribution
SEAWOLF S
occurrence rate
Transit Survey for nearby M dwarfs by 1.8m MOA-II
•Nearby (J<11) M dwarfs are sparsely distributed
in the sky (~1/deg2)
•High photometric precision (~1mmag) is
required to detect super-Earths/Neptunes
Wide FOV, 2m class telescope is ideal
the MOA-II telescope
prime-focus camera
The MOA-II telescope in New Zealand
• 1.8m mirror
• 10 x CCD (2k x 4k)
• 2.2 deg2 FOV
• Dedicated for planetary
microlensing survey
during winter (Mar. – Oct.)
Started transit
survey during
summer season
from 2013 Nov
(PI: A. Fukui).
Transit Survey for nearby M dwarfs by 1.8m MOA-II
The selected fields
Field selection/observations
• Selected 6 fields among -20° < Dec. < 5° ; each contains ~10 bright (J < 11) M
dwarfs
• One field is taken 10 times in a row with a
cadence of 80
sec
Expected
yields
Example of defocused target images • Can detect planets showing > 0.2 % transit
depth from several years survey
• Kepler detected 22 candidates showing
>0.2% transit depth among 3600 M dwarfs
• ~0.4 planets/several years can be
detected among our targets (total 65 M
dwarfs) -> similar to MEarth survey
• monitoring stellar activity for IRD targets
All-Sky Transit Survey: TESS
Led by MIT/NASA and will be launched in 2017
2 IRD science members are participating in TESS Science Working Group
TESS and IRD
• Targets
– Bright nearby stars with I = 4-13 mag (FGKM stars)
• Period of detectable planets
– typically less than 10 days (26-day monitoring for 1 field)
– up to ~60 days for JWST optimized fields
– Planetary orbits with less than 10 (60) days period lie in
habitable zone around mid (early) M stars
– expected to discover ~500 Earths / super-Earths and
Subaru IRD will contribute for RV follow-up of M dwarfs
Outline of This Talk
1. Searching new transiting planets around cool host
stars before and after IRD’s first light
2. Characterizing new transiting planets with IRD and
other telescopes / instruments
What can we learn from transits and RVs
RVs provide

minimum mass: Mp sin I

eccentricity: e
Transits provide

planetary radius: Rp

orbital inclination: i
Combined information provides

planetary mass: Mp

planetary density: ρ
Mass-Radius Relation for “Super-Earths”
Courtesy of M. Ikoma
Future transit surveys and IRD
can fill this figure out.
Theoretical models can predict
mass-radius relation for a variety
of bulk compositions, but models
are often degenerated.
How can we discriminate
compositions?
Transmission Spectroscopy
star
Transit depths depend on wavelength reflecting atmospheres
Differences of Super-Earths’ Transmission Spectra
Courtesy of Yui Kawashima
Super-Earths’ atmospheric compositions are also important
to learn origins of them -> cf. M. Ikoma’s talk
Testing Planet Migration Theories
• Transiting planets are useful to test planet migration
theories by orbital eccentricity and obliquity
– Population synthesis for small planets around M dwarfs
can predict distributions of such parameters
• IRD can measure both orbital eccentricity and
obliquity by RV observations
– obliquity by the Rossiter-McLaughlin effect
– We can provide new information to theorists
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.
Observable Orbital Obliquity
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
• We can test predictions of planet population synthesis
Conclusion
• IRD transit group is working on transit-related
science cases for Subaru IRD
• Subaru IRD will be useful for both searching and
characterizing new transiting super-Earths