Measuring the Spin-Orbit Alignments of Transiting Exoplanetary Systems: The Case for TrES-1

1. The Rossiter-McLaughlin Effect What can we learn from this effect? Formation Models of Close-in Planets How have they migrated to their current position? Planet migration mechanisms and outcomes: • Disk-Planet interaction • e.g., Lin et al. 1996 • Planets gradually migrate inward within their disks • small eccentricity and inclination • Planet-Planet interaction • e.g., Rasio & Ford 1996, Weidenschilling & Marzari 1996 • giant planets scatter one another • possible large eccentricity and inclination • subsequent tidal circularization • The Kozai migration in binary systems • e.g., Wu & Murray 2003 • eccentricity/inclination oscillations induced by separated binary companion • The RM effect is: • originally discovered in eclipsing binary systems • Rossiter 1924, McLaughlin 1924 • seen as radial velocity anomaly during a transit • dependent on the trajectory of the planet across the stellar disk • Ohta et al. 2005, Gimenez 2006, Gaudi & Winn 2007 • One can measure the sky-projected angle between the stellar spin axis and the planetary orbital axis λ Misalignment parameter λ Examples of trajectory and corresponding radial velocity anomaly of the RM effect (Gaudi & Winn 2007) Inclination (spin-orbit alignment) is an useful diagnostic -0.5 -0.05 0.05 orbital phase transit phase radial velocity and light curve Measuring the Spin-Orbit Alignments of Transiting Exoplanetary Systems: The Case for TrES-1 Norio Narita, Keigo Enya, Bun'ei Sato, Yasuhiro Ohta, Joshua N. Winn, Yasushi Suto, Atsushi Taruya, Edwin L. Turner, Wako Aoki, Motohide Tamura, Toru Yamada, Yuzuru Yoshii One can test the planet migration models by measuring the spin-orbit alignments in exoplanetary systems! The Case for TrES-1 • Observations • simultaneous spectroscopic/photometric observations • Subaru 8.2 m telescope at Mauna Kea (Hawaii) • MAGNUM 2 m telescope at Haleakala (Maui) • observing date: UT 2006 June 21 • RV precision: 10 ～ 15 m/s • photometric precision: ～ 2mmag • Parameters of TrES-1 • V = 11.8 (relatively faint) • K0V star (small rotational velocity) • duration = 150 min • i (orbital inclination) ～ 90 deg • challenging target for the RM observation constraints on λ = 30 ± 21 [deg] (a) See details in Narita et al. (2007) (astro-ph/0702707) best-fitting model (with/without constraint on VsinIs) Future Prospects of Our Project • We have demonstrated that the RM effect is detectable for a relatively faint (V～12) target • Our TrES-1 result is the first demonstration for a V～12 host star • New targets in this category have been discovered • We can measure spin-orbit alignments of those targets • We plan to conduct further RM observations for newly discovered targets with Subaru/MAGNUM telescopes in 2007 • We will present the distribution of spin-orbit alignments of transiting exoplanetary systems • Such observational information will allow us to test planet migration models in the near future