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Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)
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Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Jan 02, 2016

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Page 1: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Search for Transiting Planetsaround Nearby M Dwarfs

Norio Narita (NAOJ)

Page 2: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Outline

• Introduction of Current Status of Exoplanet Studies

• Motivation for Transiting Planets around Nearby M Dwarfs

• Roadmap and Preparations for Discoveries

– High-Precision Near Infrared Photometry

– High-Precision Near Infrared Velocimetry

• Further Studies

• Summary

Page 3: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

The First Discovery of an Exoplanet in 1995

Page 4: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

How to Measure Precise RVs of Stars

Iodine cell

Blue: without cell, Red: with cell

Star + Th-Ar

Page 5: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Year of Discovery Histogram (RV)

Page 6: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

The First Discovery of a Transiting Planet

Charbonneau et al. (2000)

HD209458b

Page 7: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

How to Search for Transiting Exoplanets

• Photometric follow-up of RV planets

– HD209458b, HD149026b …

– 7 transiting planets so far

• Transit survey and RV follow-up

Page 8: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Transit Survey

An image by TrES group

Page 9: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

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 10: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

What we can learn from transit lightcurve

stellar limb-darkeningplanet radius

ratio of planet/star size

stellar radius, orbital inclination, mid-transit time

Page 11: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

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

Page 12: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Inferring Internal Structure of Planets

Charbonneau et al. (2009)

Solid line:

H/He dominated

Dashed line:

100% H2O

Dotted line:

75% H2O, 22% Si, 3% Fe core

Dot-dashed line:

Earth-like

Page 13: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Diversity of Planetary Interior Structure

Charbonneau et al. (2006)

Page 14: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Transit Spectroscopy / Band Photometry

star

Transit depth depends on lines or bands.

Page 15: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Inferring Atmospheric Composition of GJ1214b

Green: H dominated with solar metallicity

Red: H dominated with sub-solar metallicity and cloud layer at 0.5 bar

Blue: Vapor dominated atmosphere

de Mooij et al. (2011)

Page 16: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Inferring Formation History of Planetary Systems

ejected planet

captured planets

©Newton Press

Page 17: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Recent Understanding of Planet Migration

Stellar Spin

Planetary  Orbit

As for close-in Jovian planets, tilted orbits are not so rare.

--> Various migration mechanisms indeed occur in the universe.

Page 18: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Year of Discovery Histogram (Transit)

The number of transiting planets is rapidly growing.

Page 19: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Dedicated Space Mission for Transiting Planets

CoRoTlaunched 2006/12/27

Keplerlaunched 2009/3/6

Page 20: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

TrES-2(Kepler-1)

HAT-P-7(Kepler-2)

HAT-P-11(Kepler-3)

Pre-Kepler Transiting Planets

Page 21: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

<1.25 RE

First 4 Month Kepler Planet Candidates

1235 Planet Candidates

Page 22: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

54 candidates are in

possible habitable zone.

5 are terrestrial size.

Page 23: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Kepler’s Weakness

• Kepler targets relatively faint and far stars

• Although over 1000 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

Page 24: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

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)

– PLATO (PLAnetary Transits and Oscillations of stars)

– Those are in the selection process of NASA Explore mission and ESA Cosmic Vision (late 2010s)

• Ground-based transit survey for nearby M dwarfs– MEarth lead by D. Charbonneau at Harvard

– IRD transit group (collaborating with UH etc)

Page 25: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Science Merits of Transiting Planetsaround Nearby M Dwarfs

• M dwarfs are 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 nearby 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

Page 26: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

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

Page 27: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

cf. G3 V star vs M6 V star

• G3 V star– Rs ~ 1 Rsun ~ 0.005 AU

– Assuming Rp = 1 Earth radius ~ 0.01 Rsun

– Transit Probability : Rs/a ~ 0.5%, Transit Depth : (Rp/Rs)2 ~ 0.01%

– Transit Duration : Rs P / a π ~ 14hr, Orbital Period: P ~ 365 days

• M6 V star– Rs ~ 0.1 Rsun ~ 0.0005 AU

– Assuming Rp = 1 Earth radius ~ 0.01 Rsun

– Typical HZ : a ~ 0.005 AU 、 P ~ 10 hr

– Transit Probability : Rs/a ~ 10%, Transit Depth : (Rp/Rs)2 ~ 1%

– Transit Duration : Rs P / a π ~ 20 min

Page 28: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Difficulties of M Dwarfs

• M dwarfs are very faint in visible wavelength

– Typically V > 13 even it is within 10 pc

• High precision photometry and velocimetry is difficult with current optical instruments (although a small part of targets are bright)

• Stellar activity (e.g., starspots) will also cause intrinsic noise

• But M dwarfs are much brighter in near infrared wavelength

Page 29: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Our Strategy

• We focus on high precision photometry and velocimetry in near infrared wavelength to search for transiting planets around nearby M 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 studies

Page 30: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Ongoing Studies

• I started a collaboration with a UH group, who makes a transiting planet candidate catalog and a new all-sky nearby M dwarf catalog (Gaidos, Lepine, Hilton, Mann, Chang)

• We started high precision photometric follow-up of transiting planet candidates provided by the UH group using 188 cm telescope at Okayama Astrophysical Observatory

• Subaru IRD Transit Group contributes transit observations

Page 31: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Members of the Subaru IRD Transit Group

• Norio Narita (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)

Page 32: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

How to Achieve High Precision NIR Photometry

• High precision (~1mmag or ~0.1%) photometry was considered to be very difficult previously

• It was because IR detectors tend to have numbers of bad pixels and large unevenness of sensitivity, and thus have a difficulty in precise flat-fielding

• A solution is to fix stellar position on the detector with image defocus

Page 33: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Example of Detector Image

Stars are defocused and kept off from bad pixels.

Page 34: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Example at Okayama (J band)

~1mmag is achieved for J~10 target (Fukui et al. in prep.)

Page 35: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Example at Okayama (Ks band)

~1mmag is achieved for Ks~10 target (Ohnuki et al. in prep.)

Page 36: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Example at South Africa (JHKs)

1(J) - 3(Ks) mmag is achieved for JHKs < 10 target (Narita et al. in prep.)

Page 37: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Target Selection and Our Plan

• Based on SuperWASP (ground-based transit survey) archive data, transiting planet candidates with SNR > 6 around late-K or M dwarfs have been selected (over 50 candidates are observable from Okayama)

• Low resolution spectroscopy with UH2.2m telescope is ongoing to estimate characteristics of host stars (Teff etc)

by the UH group

• 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 constrain mass

Page 38: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Okayama Proposal Accepted

Page 39: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Our Current Status

• We have achieved sufficient photometric precision to find transiting (terrestrial) planets around nearby (J < 10) M dwarfs

• We have selected transiting planet candidates from SuperWASP archive data

• Our Okayama proposals were successfully accepted (11B, 12A)

• A few targets were already observed, but were false positives

• We will follow-up ~50 candidates at Okayama in the next few years to find true planets (false positive probability is said to be about 90% from previous transit surveys)

Page 40: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Next Step

• If true transiting planets are discovered, we need to determine their orbits and masses via precise RV measurements

Subaru IRD

Page 41: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Subaru IRD Planned Specification Wavelength : 1.20-1.85 (goal 1.1-1.9) μm

Most important 1.4-1.8 μm for M stars (based on simulations using model M star spectra; table)

Spectral resolution: 70,000 ( 3pixel sampling ) Pixel scale : 0.09 arcsec/pixel Slit : 0.27 x 3 arcsec^2   (goal x 5) Fiber-fed: star + reference + sky + comb Dispersive optics : Echelle (high Blaze angle)

& VPH-Grating x 2 Velocity precision: 1 m/s w/ laser frequency comb Detector : HgCdTe 4k x 4k (or 2k x 2k) Detector temperature: ~80K Optics temperature : -50℃ Cooler: non-vibrating, LN2 Tip-Tilt: Rlimit=18 & 0.27arcsec slit usable

Courtesy: M. Tamura

Page 42: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Key Technology: Laser Frequency Comb

Spectrometer Resolution R=70,000

About 7000 lines of combFrequency stability

Comb interval

Flatness

Courtesy: M. Tamura

Generating ultra-precise wavelength ruler covering J and H band.

Designing in progress at Kurokawa-lab of TUAT

Page 43: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Fund and Scheduling

FY 1 (2010) Detailed design in each component

FY 2 (2011) Fund On-site Progress Review >> Internal review

>> CoDRFY 3 (2012)

Manufacturing and component testing with prototype(s)

FY 4 (2013) Assembling and testing

FY 5 (2014) Commissioning and observations

Grant-in-Aid for Specially Promoted Research, 22000005 (PI: M. Tamura)

Courtesy: M. Tamura

Page 44: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Further Studies after IRD Commissioning

• RV follow-up for discovered transiting planets to determine their orbits and masses

– Known planets (currently only GJ1214b) and Kepler planet candidates around M dwarfs are also excellent targets

• Transit follow-up for planets discovered by RV planet survey using IRD

• Further Studies for characterizing planets

– The Rossiter-McLaughlin effect

– Transit timing variations

– Transmission spectroscopy / multi-band transit photometry

Page 45: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

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.

Page 46: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

On Formation History of M Dwarf PlanetsAre there any tilted or retrograde terrestrial planets?

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)

Page 47: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Transit Timing Variations (TTV)

Another planet

Transit timing is not constant if there is another body in the system.

Page 48: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Merits of TTV for M Dwarfs

• TTV amplitude becomes larger than that around FGK stars because the mass of the host star is smaller

• Although TTV for hot Jupiters around FGK stars were not so fruitful since hot Jupiters do not tend to have nearby planets, Earth-like planets around M dwarfs tend to be multiple based on theoretical simulations

• TTV measurements provide clues for additional planets and Subaru IRD can confirm the existence

• Thus detections of transiting planets outside HZ are still important

Page 49: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Planetary Atmospheric Compositions and Weather

de Mooij et al. (2011)

Currently GJ1214b is the one and only target, but we can studythe diversity of planetary atmospheres in the near future

Page 50: Search for Transiting Planets around Nearby M Dwarfs Norio Narita (NAOJ)

Summary

• I think searching for transiting planets around nearby M dwarfs is one of the most important exoplanet studies we should start now

• We have achieved sufficient photometric sensitivity to detect terrestrial transiting planets around nearby M dwarfs

• 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!