June. 4, 2015 @ NAOJ Probing(the(Dynamical(History(of...
Transcript of June. 4, 2015 @ NAOJ Probing(the(Dynamical(History(of...
Probing the Dynamical History of Exoplanets: Spectroscopic Observa<ons
of Transi<ng Systems
June. 4, 2015 @ NAOJ
Teruyuki Hirano ©NASA
Outline
1. Dynamical History of Close-‐in Planets 2. Measurements of the Stellar Obliquity 3. Observa<on of the Rossiter-‐McLaughlin (RM)
Effect 4. Interpreta<on of the Past RM Result 5. Towards Smaller Planets 6. Summary
Distribu<on of Exoplanets I
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Distribu<on of Exoplanets II
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Forma<on of Close-‐in Giant Planets
The Standard Scenario → Close-‐in giants have originally formed at a few AU away from their host stars, then migrated inward by some migra<on processes.
Ø What process can make planets migrate? Ø Is there any possibility to observa<onally dis<nguish among migra<on scenarios ?
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Migra<on Processes 1. Interac<ons between proto-‐planets and proto-‐plantary disk
→ Planets had gradually migrated inward due to gravita<onal interac<ons with proto-‐planetary disk (e.g. Lin et al. 1996, Lubow & Ida 2010)
2. Planet-‐planet sca^ering (or Kozai cycles) + <dal interac<ons → When mul<ple planets form or there exists a companion star, they
interact with each other and some<mes cause orbital crossing, which can pump up eccentrici<es. Subsequent <dal interac<ons with host stars may cause orbital circulariza<on. (e.g. Cha^erjee et al. 2008, Wu et al. 2007, Fabrycky & Tremaine 2007)
6 © Weidenschilling and Marzari 1996
Migra<on Processes 1. Interac<ons between proto-‐planets and proto-‐plantary disk
→ Planets had gradually migrated inward due to gravita<onal interac<ons with proto-‐planetary disk (e.g. Lin et al. 1996, Lubow & Ida 2010)
2. Planet-‐planet sca^ering (or Kozai cycles) + <dal interac<ons → When mul<ple planets form or there exists a companion star, they
interact with each other and some<mes cause orbital crossing, which can pump up eccentrici<es. Subsequent <dal interac<ons with host stars may cause orbital circulariza<on. (e.g. Cha^erjee et al. 2008, Wu et al. 2007, Fabrycky & Tremaine 2007)
7 © Weidenschilling and Marzari 1996
→ small e and stellar obliquity
→ large e and stellar obliquity
Measurements of the Stellar Obliquity
a. The Rossiter-‐McLaughlin effect -‐> High dispersion spectroscopy during planetary transits (e.g., Queloz 2002, Winn et al. 2005)
b. Spot-‐crossing Method -‐> Modeling of anomaly in transit light-‐curves (e.g., Sanchis-‐Ojeda, et al. 2011)
c. VsinI Method -‐> Spectroscopic determina<on of the rota<on velocity + photometric determina<on of the rota<on period (e.g., Hirano et al. 2012)
d. Asteroseismology -‐> High cadence photometry of pulsa<ng stars (e.g., Chaplin et al. 2013)
e. Gravity-‐darkening Method -‐> Modeling of asymmetry in transit light-‐curves
Measurement of the stellar obliquity is a unique method to probe the dynamical history of exoplanets!
→ Kamiaka’s talk
approaching receding
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The Rossiter-‐McLaughlin (RM) Effect
←ver<cal axis: radial veliocity anomaly during a transit
during transit
Through the RM effect, we can es<mate the angle between the stellar spin axis and the planetary orbital axis, which is closely related to the planetary migra<on. 9
planet’s orbit
Results by Subaru/HDS
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Subaru RV
↑ HAT-P-16: Teff = 6158 ± 80 K λ = -8.4° ± 7.0° VsinIs = 3.9 ± 0.3 km/s T.H. + in prep.
Subaru (this work)
Keck (P08)
↑ HAT-P-7: Teff = 6350 ± 80 K λ = -132.6° +10.5° -16.3° VsinIs = 2.3 ± 0.6 km/s Narita et al. 2009
Kepler-89 (KOI-94): Teff = 6116 ± 30 K λ = -6° -11° +13° VsinIs = 8.01 ± 0.73 km/s T.H.+ 2012b, ApJ Letters This result was later confirmed by Albrecht et al. (2013)
RM Measurement for a Mul<ple Transi<ng System
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Name of Candidate Orbital Period Planet Radius
Kepler-‐89b 3.7 days 0.13 RJ
Kepler-‐89c 10.4 days 0.31 RJ
Kepler-‐89d 22.3 days 0.83 RJ
Kepler-‐89e 54.3 days 0.49 RJ
Kepler-89d
Mul<ple transi<ng systems are generally aligned!
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← RM measurements for Kepler-25 (multi-planet system):
Teff = 6190 ± 80 K λ = 7°±8° VsinIs = 8.7 ± 1.3 km/s
Albrecht et al. 2013, ApJ
Obliquity measurements for other multi-planet systems generally show good spin-orbit alignment (Sanchis-Ojeda et al. 2012, Huber et al. 2013). The only exception is Kepler-56 (multiple, but misaligned; Huber et al. 2013).
A companion is present outside of the planetary system, which might be responsible for the misalignment in Kepler-56.
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Summary of RM Measurements
Correla<on between Stellar Obliquity and Rela<ve Tidal Timescale
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↑ relative tidal damping timescale of stellar obliquity (based on Zahn 1977)
Assuming that planet-planet scatterings are the dominant channel for the formation of HJ subsequent tidal interactions “realign” the stellar spin and the planet orbital axes.
Albrecht et al. 2012
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Quiescent v.s. Chao<c migra<ons
• Quiescent migra<ons (i.e., disk-‐planet interac<ons): ü The presence of close-‐in planets in mean mo<on resonance ü Mul<ple transi<ng systems are generally aligned. ü Misaligned systems are formed by stellar internal gravity waves independently of the planets? (Rogers et al. 2012)
• Chao<c migra<ons: ü The correla<on between the stellar obliquity and rela<ve <dal damping <mescale
ü Existence of highly eccentric hot Jupiters (e.g., HD 80606b)
To Se^le This Issue…
host star Single Transi<ng System Mul<ple Transi<ng System
cool (Teff < 6250 K) many a few
hot (Teff > 6250 K) many No observa<on
Previous Targets of RM Measurements
ü One solution to partly settle the debate is to observe the RM effect for “hot multiple” systems.
ü So far, no hot multiple systems have been investigated for obliquity measurements.
ü There are a few hot multiple systems detected by Kepler (e.g., KOI-89).
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Worth a try!
Towards Smaller Planets
Limita<on of the RM Measurements
a. The RM measurements have been conducted for systems with hot Jupiters (Neptunes).
b. When the size of the transi<ng planet becomes small (~ Earth-‐sized planet), the detec<on of the RM effect becomes very challenging.
c. In order to confirm or refute possible hypothesis on the planetary migra<on (and relevant <dal interac<on), we need to expand the parameter space for which the spin-‐orbit angle is inves<gated.
→ ΔvRM 〜 - f ・ V sin Is・√(1-b^2)
Es<mate of Stellar Rota<on Periods
ü Some of the light-‐curves taken by Kepler spacecrar show periodic flux varia<ons due to rota<on of starspots.
ü From such light-‐curves, we can es<mate the rota<onal periods of planet hos<ng stars.
KOI 988
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Es<ma<on of Stellar Inclina<ons by Starspots
ü The rotational period Ps of the host star is estimated by Kepler photometry. ü The projected rotational velocity (V sin Is) and stellar radius are estimated by spectroscopy.
We can estimate stellar inclination Is. a. Since the orbital inclina<on of a transi<ng exoplanet is close to 90°, a small
value of Is implies a spin-‐orbit misalignment.
b. This method can be applied regardless of the size of the planet, enabling us to discuss spin-‐orbit alignment/misalignment for smaller exoplanets.
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Results 1
x axis -> y axis ->
rotational velocities estimated by Kepler photometry
projected rotational velocities estimated by spectroscopy
Solid line indicates Veq = V sin Is, suggesting spin-orbit alignments.
KOI-261 may have a possible spin-orbit misalignment along the line-of-sight.
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We observed about 10 KOI systems and estimated VsinIs along with stellar radii.
T.H.+ 2012, ApJ, 756, 66
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Results 2
ü All the systems here have only Earth- or Neptune-sized planets. ü Some multiple systems show possible spin-orbit misalignment.
We observed additional 25 systems.
T.H.+ 2014, ApJ
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Posterior distribu<ons of Is
ü We computed the posterior distribution of Is for each system. ü The solid lines indicate the averaged posteriors for single and multiple systems. ü The two distributions (red and blue) seem slightly different from each other.
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Summary
1. Measurements of the stellar obliquity have revealed a diversity in the spin-‐orbit rela<on, and yielded new hypotheses on the dynamical origin of exoplanets.
2. Observa<onal results of the RM measurement imply that some close-‐in giant planets have experienced quiescent migra<on (e.g., Kepler-‐89), while others are produced by more chao<c processes. The reason for this discrepancy between the two dynamical origins is not known.
3. Measurement of the stellar inclina<on is a unique technique to discuss spin-‐orbit rela<ons for systems with smaller planets. Previous observa<on showed that transi<ng systems with small planets generally have good spin-‐orbit alignment. The distribu<ons of stellar inclina<ons for single and mul<ple systems show a slight difference (Morton & Winn 2014).