transiting exoplanet search and characterization with subaru's new infrared doppler instrument...
TRANSCRIPT
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
Charbonneau et al. (2000)
Transits of HD209458bMazeh et al. (2000)
RVs of HD209458b
RVs can predict possible transit times
How often does it happen?
Some Characteristics of Transiting Planets
stellar radius :
planetary radius :
Toward Earthsemi-major axis :
orbital period :
Transit Probability :
Transit Depth :
Transit Duration :
~ Rs/a
~ (Rp/Rs)2
~ 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
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 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).
the MOA-II telescopeprime-focus camera
Transit Survey for nearby M dwarfs by 1.8m MOA-II
• 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
The selected fields
Expected yields• 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
Galactic plane
Example of defocused target images
Field selection/observations
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 RVsRVs 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”
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?
Courtesy of M. Ikoma
Transmission Spectroscopy
star
Transit depths depend on wavelength reflecting atmospheres
Differences of Super-Earths’ Transmission Spectra
Super-Earths’ atmospheric compositions are also important to learn origins of them -> cf. M. Ikoma’s talk
Courtesy of Yui Kawashima
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
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.
Observable Orbital ObliquityAre there any tilted or retrograde super-Earths?
λ : sky-projected angle betweenthe 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