Title: Measuring Spin-Orbit Alignment Angles of Transiting Exoplanets with the Subaru HDS
Author(s): Norio Narita and the Subaru HDS collaboration team
Abstract:

In transiting planetary systems, one can measure the sky-projected
angle between the stellar spin axis and the planetary orbital axis
(spin-orbit alignment angle) by monitoring the Rossiter-McLaughlin effect.
The effect is observed as an anomaly of radial velocity from the Kepler
motion during transits. Thus one can measure the spin-orbit alignment
angle by spectroscopic transit observations. The angle of two axes has
become widely recognized to be an useful diagnostic for discriminating
planet migration theories, including Type II migration models,
planet-planet scattering models, or the Kozai migration models.
We present results of Subaru observations aimed to measure spin-orbit
alignment angles of several transiting exoplanets. As a result, we found
that almost all observed systems have either small or consistent with
zero alignment angles. Our results would be consistent with the predictions
of standard Type II migration models. On the other hand, there is an
exception which is reported to have a large misalignment, XO-3b; an
eccentric massive planet with the orbital period of 3.19 days. Since
currently XO-3b is the only exception that has a large misalignment
angle, further observations of spin-orbit alignment angles especially
for eccentric transiting planets (including a confirmation for XO-3b)
are desired in order to test planet migration theories by observations.