toward detections and characterization of habitable transiting exoplanets
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Toward Detections and Characterization of Habitable Transiting Exoplanets. Norio Narita (NAOJ). Outline. Current Status and Next Step to Detect Habitable Transiting Exoplanets Methodology and Prospects of Characterizing Habitable Transiting Exoplanets Summary. - PowerPoint PPT PresentationTRANSCRIPT
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Toward Detections and Characterization of Habitable Transiting Exoplanets
Norio Narita (NAOJ)
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Outline
• Current Status and Next Step to Detect Habitable
Transiting Exoplanets
• Methodology and Prospects of Characterizing
Habitable Transiting Exoplanets
• Summary
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Various Exoplanet Detection Methods
• Radial velocity method– First detection in 1995, 500+ planets
• Transit method (this talk)– First detection in 2000, 400+ planets, 3000+ candidates
• Gravitational microlensing method– First detection in 2004, 20+ planets
• Direct imaging method– First detection in 2008, 10+ planets/brown dwarfs
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What is Planetary Transit?
primary eclipse= transit
secondary eclipse
planetary orbit
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The First Discovery of a Transiting Exoplanet
Charbonneau et al. (2000)
Transits of “hot Jupiter” HD209458b
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Features of Transits
• Can determine planetary radius
– Other methods cannot do this
• Can determine planetary true mass and density
when combined with the RV method
– The density is important information to infer planetary
internal structure (gas, rock, iron, etc)
• Can characterize planetary atmosphere and orbit
(later)
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How to Detect Transiting Exoplanets
One can search for periodic dimming from this kind of data
From TrES survey
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Space Mission for Transiting Planet Search
CoRoTlaunched 2006/12/27
Keplerlaunched 2009/3/6
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Kepler Field of View
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TrES-2(Kepler-1)
HAT-P-7(Kepler-2)
HAT-P-11(Kepler-3)
Pre-Kepler Transiting Planets
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<1.25 RE
First 4 Month Kepler Planet Candidates
1235 Planet Candidates
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2740 planet candidates (2013/01) -> 3277 candidates
(2013/06)
<1.25 RE
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54 candidates are in
possible habitable zone.
5 are terrestrial size.
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Possible Habitable Planet reported in 2011
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Habitable Super-Earths reported in 2013
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Habitable Super-Earths reported in 2013
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(Sub-)Earth-sized Planets
Earth-sized planet Kepler-20f
Mars-sized planet KOI-961.03 (renamed as Kepler-42d)
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Kepler’s Weakness
• Kepler targets relatively faint and far stars
– Although over 3000 candidates discovered, RV follow-ups for all 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 bright stars to detect terrestrial planets in habitable zone
• Ground-based transit survey for nearby M dwarfs– MEarth lead by D. Charbonneau at Harvard
– Other teams all over the world
– IRD transit group
• Space-based all-sky transit survey for bright stars– TESS (Transiting Exoplanet Survey Satellite) by MIT team
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All-Sky Transit Survey: TESS
Led by MIT and approved by NASA in April 2013.
TESS will be launched in 2017.
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TESS Discovery Space
• 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 and super-Earths
(including expected 5±2 habitable planets) by early 2020s
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Outline
• Current Status and Next Step to Detect Habitable
Transiting Exoplanets
• Methodology to Characterize Transiting Exoplanets
and Future Prospects
• Summary
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What we would like to study for Habitable Planets?
1. What are components of their atmospheres?
– Important information to infer habitability
– Do they have hydrogen atmosphere?
– Hydrogen is strong green house gas and affect habitability
(Pierrehumbert & Gaidos 2011)
2. How do they form?
– Uncovering their migration mechanism
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Characterization of their Atmospheres
star
Transit depths depend on lines / wavelength reflecting atmosphere
Transmission Spectroscopy
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Differences of Transmission Spectra
Super-Earths may have hydrogen-rich atmosphere,which has a large atmospheric scale height
Courtesy of Yui Kawashima
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Discriminating Hydrogen-Rich Atmosphere
Miller-Ricci & Fortney (2010) Solar abandance atmosphere
One can tell whether a planet has hydrogen-rich atmosphere or not by multi-color transit photometry
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Other Spectroscopic Features
Benneke & Seager (2012)
Optilal-NIR region has some features of atmospheric compositions
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Transmission Spectroscopy by MOS
• One can do transmission spectroscopy using MOS
(multi-object spectrograph) instruments
– VLT/FORS2, Gemini/GMOS, Magellan/MMIRS already
reported excellent results
– We will try with Subaru/MOIRCS & FOCAS next month
• Simultaneously observe target and reference stars
– using very wide slit (~10”) to avoid light-loss from slits
– integrate wavelength to create high precision light curves
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Example by Bean et al. (2010)
• Instrument: VLT/FORS2
• Target: GJ1214b (V=14.7)
• Integration: 20 nm (R ~ 30)
• Precision: 331-580 ppm
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Recent Example by Gibson et al. (2012)
• Instrument: Gemini South/GMOS
• Target: WASP-29b (V=11.3)
• Integration: about 15 nm (R ~ 40)
• Precision: ~400 ppm
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Optical MOS is useful to see Rayleigh Slope
One can tell whether the atmosphere is dominated by hydrogen or not
and possible existence of haze particle
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Kepler-22 Properties
• Planet– Period: 289.86 days
– Radius: 2.4 RE (super-Earth), transit depth: 500 ppm
– gaseous mini-Neptune or large ocean planet?
• Host Star– G5V star
– B=11.5, R=11.7, J=10.5, H=10.2
• TMT’s optical MOS instrument (WFOS) can measure the
Rayleigh slope in optical wavelength
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Transmission Spectroscopy with Space Telescopes
H2O CO2
Simulated ~100hr detections of molecules in atmospheres of habitable transiting super-Earths (Deming et al. 2009)
JWST/SPICA can characterize NIR-MIR transmission spectra
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What E-ELT’s High Dispersion Spectrographs Can
• Transmission spectroscopy
– Can detect atmospheric atomic/molecular absorptions
• High dispersion instruments can directly detect
planet’s shadow and can measure orbital obliquity
– Important information to infer ``how do they form?’’
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What is Planet’s Shadow?
planet hides an approaching side planet hides a receding side
planet planetstar
Planet removes a part of velocity component of stellar lines
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What happen to Shape of Stellar Lines
Stellar lines of HAT-P-2 taken with Keck/HIRES
Albrecht et al. (2013)
optimal kernel of lines
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Planet’s Shadow in Stellar Lines
transit
This shadow shows a trajectory of the planet in front of the star
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What we can learn by planet’s shadow
The obliquity tells us planetary migration mechanisms of exoplanets.
Like our Solar System or experienced dynamical migration.
Planetary Orbital Plane
PlanetPlanetary Orbital Axis
Stellar Spin Axis
Star
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Capability of E-ELT’s High Dispersion Spectrographs
• Can detect planet’s shadow and measure orbital
obliquity of smaller planets
– TMT can reveal migration history for smaller planets
– which means, TMT can answer an aspect of “how
planetary systems form”
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Summary
• Ongoing and future transit survey (TESS) will discover
habitable transiting planets in Solar neighborhood
• Future E-ELTs and space telescopes will work on
characterizing their atmospheres and formation
mechanisms