Testing Planet Migration Theories by Observations of Transiting Exoplanetary Systems

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Testing Planet Migration Theoriesby Observations
of TransitingExoplanetary Systems

• University of Tokyo
• Norio Narita

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Contents

• Introduction (15 min)
• Diversity of Extrasolar Planets
• Planet Migration Theories
• Motivation (10 min)
• Transits and the Rossiter-McLaughlin Effect
• Recent Results (15 min)
• Simultaneous Subaru / MAGNUM Observations
• Analysis and Results
• Conclusion and Future Prospects (3 min)
• Significance of Our Results
• New Targets and Prospects

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Discovery of extrasolar planets
The first extrasolar planet 51 Peg. b was
discovered by radial velocity measurements in
1995.
More than 200 extrasolae planets have been
discovered so far.
We can discuss statistics of their distribution.
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Diversity of extrasolar planets
Jupiter
Semi-major axis Planet minimum mass Distribution
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Diversity of extrasolar planets
hot Jupiters
1 AU
(Close-up of the distribution)
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Diversity of extrasolar planets
Eccentric Planets
Jupiter
Semi-major axis Eccentricity Distribution
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How do they form?

• Giant planets lie at 0.1AU
• should originally form at larger orbital
  distances
• planetary migration to inner orbits
• Eccentric planets are common
• would have mechanisms of eccentricity excitation
• How can we explain these features?
• gravitational interactions with other bodies in
  protoplanetary disk

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Planet migration theories

• disk-planet interaction
• Type I II migration
• resultant planets would not have large
  eccentricity
• planet-planet interaction
• jumping Jupiter model
• have possibilities to produce large eccentricity
• planet-binary companion interaction
• Kozai oscillation in binary planetary systems
• also have possibilities to produce large
  eccentricity
• explain HD 80606 system (e0.927, Wu Murray
  2003)

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Type I II migration

• planetary cores form beyond the snow line
• the cores interact with the surrounding disk
• planets migrate inward due to torque exchange
  with the disk
• Type I migration less than 10ME
• Type II migration more than 10ME
• damping eccentricities and also inclination

Type I migration
Type II migration
(Leiden Observatory Group)
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Jumping Jupiter model

• giant planets interact with each other in
  multi-planet systems
• leads to orbital instability
• one planet is thrown into close-in orbit
• the planet obtains eccentricity and inclination

Note this inclination is relative to the
initial orbital plane
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Jumping Jupiter model
inclination
eccentricity
90 of samples have inclination of more than 10
deg
produce large eccentricities
periastron
semi-major axis
periastron distance finally become semi-major
axis by tidal evolution in hot region
Marzari Weidenschilling (2002)
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Note Tidal evolution

• time scale for planetary orbit circularization
• time scale for stellar spin/planetary orbit
  coplanarization
• s star, p planet, adopting values for HD
  209458b as a typical case
• P orbital/rotation period, k tidal Love
  number,
• Q tidal quality factor (cf. 6104 lt QJup lt
  2106)
• Typically tcopl is much longer than tcirc

Mardling (2007), Winn et al. (2005)
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Kozai mechanism

• distant binary companion perturbs a planetary
  orbit
• leads to Kozai oscillation
• due to conservation of angular momentum
• the planetary orbit oscillates high/low
  eccentricity/inclination
• the planet migrates by tidal evolution

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Kozai migration
eccentricity
periastron
inclination
Wu Murray (2003)
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Differences in outcomes

• disk-planet interaction
• negligible eccentricity and inclination
• mainstream of migration theories
• but cannot explain eccentric planets
• planet-planet interaction
• possible large eccentricity and inclination
• subsequent tidal evolution damps eccentricity
• would explain distribution of eccentric planets
• planet-binary companion interaction
• large eccentricity and inclination

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Motivation

• How can we test these theories by observations?
• eccentricity and inclination are possible clues
• but eccentricity may be damped within planets
  age
• inclination (angle between initial and final
  orbital plane) would be a good diagnostic
• Stellar spin axis would preserve initial orbital
  axis
• the inclination is equal to the stellar spin axis
  and the planetary orbital axis (spin-orbit
  alignment)
• But can we observe/constraint spin-orbit
  alignments of exoplanetary systems?

Note Assumption
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Transiting extrasolar planets
Planets pass in front of their host star.
Charbonneau et al. (2000)
periodic dimming in photometry
The first transiting planet HD 209458b was
reported in 2000.
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What can we learn from transiting planets?

• Radial Velocity
• semi-major axis a, minimum mass Mp sin i
• Period P, eccentricity e
• Transit Photometry
• orbital inclination iorb?radius ratio Rp/Rs
• by combining spectroscopy radius Rp, density ?
• Secondary Eclipse
• thermal emission of planetary surface
• Transmission Spectroscopy
• search for atmospheric components
• Na, H, C, O, H2O, SiO detections were reported in
  HD 209458b
• (Subaru observations for HD 189733b tomorrow)

Note this inclination is relative to the sky
plane
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Radial Velocity during Transit
Transiting planet hides stellar rotation.
star
planet
planet
hide approaching side ? appear to be receding
hide receding side ? appear to be approaching
Radial velocity would have anomalous
excursion during transit.
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The Rossiter-McLaughlin effect
This effect was originally reported in eclipsing
binary systems.
ß Lyrae Rossiter 1924, ApJ, 60, 15
Algol McLaughlin 1924, ApJ, 60, 22
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RM effect in transiting exoplanetary system
ELODIE on 193cm telescope
Queloz et al. (2000)
The RM effect was detected in HD 209458b in 2000.
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What can we learn from the RM effect?
RV anomaly
time
examples of trajectory
Ohta, Taruya Suto (2005)
Radial velocity anomaly reflects planet
trajectory.
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Definition of ?
? sky-projected angle between the stellar spin
axis and the planetary orbital axis
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Planetary trajectories and ?
We can measure ? by observations of the RM effect.
Gaudi Winn (2007)
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Summary of introduction and motivation

1. There are several different planet migration
   theories.
2. Each theory has different distributions of
   eccentricity and inclination.
3. We can observe the RM effect in transiting
   exoplanetary systems.
4. We can measure ?(sky-projected spin-orbit
   alignment) via the RM effect.
5. ? is an useful diagnostic for testing planet
   migration theories.

A
B
E
C
D
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Our recent observations
Brief summary Target TrES-1 (V11.8) ? the
faintest target so far Observation Simultaneous
Subaru/MAGNUM observations Challenge the first
RM observation for Subaru MAGNUM Result
succeeded in detection of the RM effect and
placed a constraint on
? Significance 1 extended targets of the RM
observations to
fainter systems Significance 2 discovery of a
possible misaligned system
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Backgrounds of the RM observations
History of discoveries of target systems before
2005 HD 209458 2000, V7.65 TrES-1
2004, V11.8 HD 149026 2005, V8.15 HD 189733
2005, V7.67

The RM observations were conducted for brighter
targets with Keck/HIRES HD 209458 Winn et al.
2005 HD 189733 Winn et al. 2006 (HD 149026
Wolf et al. 200?)
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Possible targets of the RM observations
Possible targets ? Transiting systems brighter
than V12 (for which we can detect the RM effect
with Subaru/HDS)
Our target TrES-1, V11.8 The first challenge
for a fainter (V12) target (also the first RM
observation for Subaru/HDS)
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TrES-1

• Discovered with 10cm telescope (Alonso et al.
  2004)
• V11.8?K0V?V sin Is 1.08 0.30 km/s)
• Poor radial velocity measurements due to its
  faintness.
• The star has several spots.

UpperTrES-1 LowerHD 209458
?Charbonneau et al. (2007)
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Simultaneous Subaru/MAGNUM observations
TrES-1 observations with 2 telescopes in Hawaii
(UT 2006/6/21)
Photometry with MAGNUM at Haleakala
Radial velocity measurement with Subaru/HDS
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RV measurements with Subaru/HDS

• 20 samples
• R 45000
• Exposure time 15 min
• Seeing 1.0 arcsec
• S/N 60 (with iodine cell)
• Radial velocity analysis by Sato et al. (2002)
• RV precision 10 15 m/s

Radial velocities obtained with Subaru/HDS
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Photometry with MAGNUM

• 184 samples
• Band V
• Exposure time 40 or 60 sec
• No spot event
• Photo. precision 2 mmag
• Timing precision 30 sec

V band transit light curve obtained with MAGNUM
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RV model and parameters

• incorporating published data
• Keck 12 ( 7 5 ) RV samples
• FLWO 1149 (3 transits) photometric samples
• RM modeling with Ohta, Taruya, Suto
  formula(2005)
• Simultaneous fitting of radial velocity and
  photometry
• including the RM effect
• 15 free parameters
• K, VsinIs, ? for radial velocity
• iorb, uV, uz, Rs, Rp/Rs for photometry
• v1, v2, v3 offsets for radial velocity datasets
• Tc(234), Tc(235), Tc(236), Tc(238) time of
  transit center

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Note Constraints on VsinIs

• External constraint on VsinIs for TrES-1
• VsinIs 1.08 0.30 km/s (Laughlin et al. 2005)
• Fitting with (a) / without (b) considering the
  constraint

• ?2 minimization with AMOEBA (Numerical Recipes)

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Results of RV fitting
-0.5
0.05
0
0
orbital phase
transit phase
a with, b without
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Constraints on VsinIs and ?
(a) VsinIs 1.3 0.3 km/s, ? 30 21
deg (b) VsinIs 2.5 0.8 km/s, ? 48
17 deg
Contours ??21,00, ??22.30, ??24.00, ??26.17
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Summary of Our Recent Results

• We detected the RM effect in TrES-1 (V12)
• TrES-1 is the faintest target so far
• We confirm that similar observations are possible
  for other faint systems
• We put a constraint on ? in TrES-1 for the first
  time
• large uncertainty, but at least we confirmed that
  the planet orbits in a prograde manner
• possible misaligned (over 10 deg) system
• additional RM observations would pin down ?
• the first candidate of the jumping Jupiter model

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Whats next?
New targets were discovered in 2006 2007

• 4 ground-based transit survey teams (XO, TrES,
  HAT, WASP) succeeded in detecting new transiting
  systems
• all transit survey teams target V less than 12
• also ESAs satellite mission (CoRoT) started in
  2007
• 2006 XO-1, TrES-2, HAT-P-1, WASP-1, WASP-2
• 2007 CoRoT-1, TrES-3, XO-2, XO-3, HAT-P-2, GJ
  436
• (recent news) XO-4, TrES-4, HAT-P-3, HAT-P-4,
  more to come!

observational / statistical studies have become
possible
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Future Prospects

• We can measure the RM effect of new transiting
  systems
• By measuring the distribution of spin-orbit
  alignment,
• we can test planet migration theories
• already we have
• possible misaligned target TrES-1 ? further
  constraint on ?
• at least 15 new targets
• We can present observational / statistical
  distribution of spin-orbit alignment within
  several years

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