1. 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
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
Inclination (spin-orbit alignment) is an useful diagnostic
The Rossiter-McLaughlin Effect
What can we learn from this effect?
Misalignment parameter λ
Examples of trajectory and corresponding radial velocity anomaly of the RM effect
(Gaudi & Winn 2007)
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
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
orbital phase
transit phase
-0.5
-0.05
0.05
radial velocity and light curve
constraints on λ
= 30 ± 21 [deg] (a)
See details in Narita et al. (2007)
(astro-ph/ )
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