discriminating migration mechanisms of tilted or eccentric planetary systems
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Discriminating Migration Mechanisms of Tilted or Eccentric Planetary Systems. Norio Narita (NAOJ/University of Hawaii). Special thanks to my collaborators. Measurements of the Rossiter -McLaughlin effect Teruyuki Hirano, Bun’ei Sato, Josh Winn, Wako Aoki, Motohide Tamura - PowerPoint PPT PresentationTRANSCRIPT
Discriminating Migration Mechanisms ofTilted or Eccentric Planetary Systems
Norio Narita(NAOJ/University of Hawaii)
Special thanks to my collaborators• Measurements of the Rossiter-McLaughlin effect
– Teruyuki Hirano, Bun’ei Sato, Josh Winn, Wako Aoki, Motohide Tamura
• SEEDS NS category/RV sub-category (Today’s talk)– Tomoyuki Kudo, Ryo Kandori, Bun’ei Sato, Ryuji Suzuki,
Masayuki Kuzuhara, Yasuhiro Takahashi, Motohide Tamura, and all SEEDS/HiCIAO/AO188 members
• Photometric transit observations (incl. TTV)– Akihiko Fukui, Takuya Suenaga, Masayuki Kuzuhara, Hiroshi
Ohnuki, Bun’ei Sato, Osamu Ohshima, Motohide Tamura, and Japanese Transit Observation Network members
Motivation to study exoplanetary orbits
How do planetary systems form?
Planetary orbits would provide us information
about formation histories of exoplanetary systems!
Semi-Major Axis Distribution of Exoplanets
Need planetary migration mechanisms!
Snow line
Jupiter
Eccentricity Distribution
Need planet-planet scattering and/or Kozai mechanism.
Jupiter
Eccentric Planets
What we learned from RM measurements
Tilted or retrograde planets are not rare (1/3 planets are tilted)
p-p scattering or Kozai mechanism occur in exoplanetary systems
Stellar Spin
Planetary Orbit
Remaining ProblemsWhich model is a dominant migration mechanism?
The number of RM samples is still insufficient to answer statistically.Morton & Johnson (2010)
Remaining Problems
One cannot distinguish between p-p scattering and Kozai
migration for each planetary system
To specify a planetary migration mechanism for each system,
we need to search for counterparts of migration processes
long term radial velocity measurements (< 10AU)
direct imaging (> 10-100 AU)
Motivation for high-contrast direct imaging
The results of RM measurements suggest that a significant
part of planetary systems may have wide separation massive
bodies (e.g., scattered massive planets or brown dwarfs, or
binary companions)
direct imaging for tilted or eccentric planetary systems may
allow us to specify a migration mechanism for each planetary
system
SEEDS ProjectSEEDS: Strategic Exploration of Exoplanets and Disks with Subaru
First “Subaru Strategic Observations” PI: Motohide Tamura
Using Subaru’s new instruments: HiCIAO & AO188
total 120 nights over 5 years (10 semesters) with Subaru Direct imaging and census of giant planets and brown dwarfs around
solar-type stars in the outer regions (a few - 40 AU) Exploring proto-planetary disks and debris disks for origin of their
diversity and evolution at the same radial regions
Subaru’s new instrument: HiCIAO• HiCIAO: High Contrast Instrument for next
generation Adaptive Optics• PI: Motohide Tamura (NAOJ)
– Co-PI: Klaus Hodapp (UH), Ryuji Suzuki (TMT)• 188 elements curvature-sensing AO and will
be upgraded to SCExAO (1024 elements)• Commissioned in 2009• Specifications and Performance
– 2048x2048 HgCdTe and ASIC readout– Observing modes: DI, PDI (polarimetric mode),
SDI (spectral differential mode), & ADI; w/wo occulting masks (>0.1")
– Field of View: 20"x20" (DI), 20"x10" (PDI), 5"x5" (SDI)
– Contrast: 10^-5.5 at 1", 10^-4 at 0.15" (DI)– Filters: Y, J, H, K, CH4, [FeII], H2, ND– Lyot stop: continuous rotation for spider block
An example of this study: Target HAT-P-7
not eccentric, but retrograde (NN+ 2009b, Winn et al. 2009c)
very interesting target to search for outer massive bodies
NN et al. (2009b) Winn et al. (2009c)
ObservationsSubaru/HiCIAO Observation: 2009 August 6
Setup: H band, DI mode (FoV: 20’’ x 20’’)
Total exposure time: 9.75 min
Angular Differential Imaging (ADI: Marois+ 06) technique with
Locally Optimized Combination of Images (LOCI: Lafreniere+ 07)
Calar Alto / AstraLux Norte Observation: 2009 October 30
Setup: I’ and z’ bands, FoV: 12’’ x 12’’
Total exposure time: 30 sec
Lucky Imaging technique (Daemgen+ 09)
Result Images
Left: Subaru HiCIAO image, 12’’ x 12’’, Upper Right: HiCIAO LOCI image, 6’’ x 6’’Lower Right: AstraLux image, 12’’ x 12’’
N
ENN et al. (2010b)
Characterization of binary candidates
Based on stellar SED (Table 3) in Kraus and Hillenbrand (2007).Assuming that the candidates are main sequence stars
at the same distance as HAT-P-7.
projected separation: ~1000 AU
Can these candidates cause Kozai migration?
The perturbation of a binary must be the strongest in the
system to cause the Kozai migration (Innanen et al. 1997)
If perturbation of another body is stronger
Kozai migraion refuted
conditional equation:
(smaller bodies are allowed)
If such an additional body does not exist
both Kozai and p-p scattering still survive
An additional body ‘HAT-P-7c’
HJD - 2454000
Winn et al. (2009c) 2008 and 2010 Subaru data(unpublished)
2007 and 2009 Keck data
Long-term RV trend ~20 m/s/yr is ongoing from 2007 to 2010
constraint on the mass and semi-major axis of ‘c’
(Winn et al. 2009c)
Result for the HAT-P-7 case
We detected two binary candidates, but the Kozai migration
was excluded because perturbation by the additional body is
stronger than that by companion candidates
As a result, we conclude that p-p scattering is the most likely
migration mechanism for this system
We can constrain planetary migration mechanisms by this
methodology.
Ongoing and Future Subaru Observations
There are numbers of tilted and/or eccentric transiting planets
These planetary systems are interesting targets that we may be
able to discriminate planetary migration mechanisms
No detection is still interesting to refute Kozai migration
Detections of outer massive bodies are very interesting
but It would take some time to confirm such bodies
Waiting 2nd Epoch and more…
Summary
RM measurements have discovered numbers of tilted and
retrograde planets
Tilted or eccentric planets are explained by p-p scattering or
Kozai migration --> those mechanisms are not rare
One problem is that we cannot distinguish between p-p
scattering and Kozai migration from orbital tilt or eccentricity
High-contrast direct imaging can resolve the problem and may
allow us to specify migration mechanism for each system
Further results will be reported in the near future!
How to constrain migration mechanismStep 1: Is there a binary candidate?
No
Kozai migration by a binary companion is excluded
If a candidate exist → step 2
both p-p scattering and Kozai migration survive
need a confirmation of true binary nature
• common proper motion
• common peculiar radial velocity
• common distance (by spectral type)
How to constrain migration mechanism
Step 2: calculate restricted region for Kozai migration
The Kozai migration cannot occur if the timescale of orbital precession
due to an additional body PG,c is shorter than that caused by a binary
through Kozai mechanism PK,B (Innanen et al. 1997)
If any additional body exists in the restricted region
Kozai migraion excluded
search for long-term RV trend is very important
If no additional body is found in the region
both Kozai and p-p scattering still survive
Future AO upgrade: SCExAO from 2011Subaru Coronagraphic Extreme-AO System
AO188 limit
SCExAO limit