Probing the Dynamical History of Exoplanets: Spectroscopic Observa<ons of Transi<ng Systems

Transcription

1 June. 4, NAOJ Probing the Dynamical History of Exoplanets: Spectroscopic Observa<ons of Transi<ng Systems NASA Teruyuki Hirano

2 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

3 Distribu<on of Exoplanets I 1 planet mass [M J ] B C A Snow Line semi-major axis [AU]

4 Distribu<on of Exoplanets II 1 orbital eccentricity semi-major axis [AU]

5 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? 5

6 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 21) 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. 28, Wu et al. 27, Fabrycky & Tremaine 27) 6 Weidenschilling and Marzari 1996

7 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 21) small e and stellar obliquity 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. 28, Wu et al. 27, Fabrycky & Tremaine 27) large e and stellar obliquity 7 Weidenschilling and Marzari 1996

8 Measurements of the Stellar Obliquity Measurement of the stellar obliquity is a unique method to probe the dynamical history of exoplanets! a. The Rossiter- McLaughlin effect - > High dispersion spectroscopy during planetary transits (e.g., Queloz 22, Winn et al. 25) b. Spot- crossing Method - > Modeling of anomaly in transit light- curves (e.g., Sanchis- Ojeda, et al. 211) c. VsinI Method - > Spectroscopic determina<on of the rota<on velocity + photometric determina<on of the rota<on period (e.g., Hirano et al. 212) d. Asteroseismology - > High cadence photometry of pulsa<ng stars (e.g., Chaplin et al. 213) e. Gravity- darkening Method - > Modeling of asymmetry in transit light- curves Kamiaka s talk

9 The Rossiter- McLaughlin (RM) Effect λ = λ = 5 approaching receding planet s orbit RV anomaly during transit RV anomaly ver<cal axis: radial veliocity anomaly during a transit time [h] time [h] 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

10 Results by Subaru/HDS 4 Subaru RV 2!v [m s -1 ] -2-4 Subaru (this work) Keck (P8) Residual [m s -1 ] Orbital Phase HAT-P-16: Teff = 6158 ± 8 K λ = -8.4 ± 7. VsinIs = 3.9 ±.3 km/s T.H. + in prep. HAT-P-7: Teff = 635 ± 8 K λ = VsinIs = 2.3 ±.6 km/s Narita et al. 29

11 RM Measurement for a Mul<ple Transi<ng System Name of Candidate Orbital Period Planet Radius Kepler- 89b 3.7 days.13 RJ Kepler- 89c 1.4 days.31 RJ Kepler- 89d 22.3 days.83 RJ Kepler- 89e 54.3 days.49 RJ 4 2 Kepler-89 (KOI-94): v [m s -1 ] Residual [m s -1 ] Kepler-89d Orbital Phase Teff = 6116 ± 3 K λ = VsinIs = 8.1 ±.73 km/s T.H.+ 212b, ApJ Letters This result was later confirmed by Albrecht et al. (213)

12 Mul<ple transi<ng systems are generally aligned! 15 1 RM measurements for Kepler-25 (multi-planet system): RV (m s 1 ) Teff = 619 ± 8 K λ = 7 ±8 VsinIs = 8.7 ± 1.3 km/s 15 O C (m s 1 ) Time (hr) Albrecht et al. 213, ApJ Obliquity measurements for other multiplanet systems generally show good spinorbit alignment (Sanchis-Ojeda et al. 212, Huber et al. 213). The only exception is Kepler-56 (multiple, but misaligned; Huber et al. 213). A companion is present outside of the planetary system, which might be responsible for the misalignment in Kepler-56.

13 Summary of RM Measurements 18 λ proj. obliquity [deg] HAT-P-11 b WASP-8 b HD 866 b HD b 8 v sin i star [km s -1 ] T eff [K] Albrecht et al. 212

14 Correla<on between Stellar Obliquity and Rela<ve Tidal Timescale Albrecht et al. 212 λ proj. obliquity [deg] HAT P 32 b HAT P 7 b WASP 8 b WASP 33 b WASP 12 b XO 3 b KOI 13 b HAT P 11 b HD 866 b HD b relative tidal dissipation timescales τ CE τ RA [yr] 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.

15 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. 212) 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 866b)

16 To Se^le This Issue Previous Targets of RM Measurements host star Single Transi<ng System Mul<ple Transi<ng System cool (Teff < 625 K) many a few hot (Teff > 625 K) many No observa<on 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). Worth a try! proj. obliquity [deg] v sin i star [km s -1 ] HAT-P-11 b WASP-8 b HD 866 b HD b T eff [K]

17 Towards Smaller Planets

18 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. ΔvRM - f V sin Is (1-b^2) 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.

19 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. Relative flux KOI BJD [days] ü From such light- curves, we can es<mate the rota<onal periods of planet hos<ng stars. Power Period of rotation [days]

20 Es<ma<on of Stellar Inclina<ons by Starspots 534/%-).&#+-43)46+$ 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. λ 1 I. I$ 2 $-%334&)$5+/)46+$ 7!"#$%&'%&($)*+&%,-+./ We can estimate stellar inclination Is. a. Since the orbital inclina<on of a transi<ng exoplanet is close to 9, 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.

21 Results 1 We observed about 1 KOI systems and estimated VsinIs along with stellar radii. V sin I s [km s -1 ] multiple I s =9 o 269 I s =45 o I s =3 o x axis -> y axis -> rotational velocities estimated by Kepler photometry projected rotational velocities estimated by spectroscopy V eq [km s -1 ] Solid line indicates Veq = V sin Is, suggesting spin-orbit alignments. T.H.+ 212, ApJ, 756, 66 KOI-261 may have a possible spin-orbit misalignment along the line-of-sight.

22 Results 2 We observed additional 25 systems. V sin I s [km s -1 ] (a) single I s =9 o I s =45 o I s =3 o 189 V sin I s [km s -1 ] (b) multi I s =9 o I s =3 o I s =45 o V eq [km s -1 ] V eq [km s -1 ] T.H.+ 214, ApJ ü All the systems here have only Earth- or Neptune-sized planets. ü Some multiple systems show possible spin-orbit misalignment.

23 Posterior distribu<ons of Is Probability Density blue single red multi black isotropic I s [radian] 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.

24 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 214).