Spectroscopic Studies of Transiting Planetary Systems

As of December 2007, radial velocity measurements and planetary transit surveys for nearby stars have already identified more than 250 planets around other stars. These “extrasolar planets” opened a new field of astronomy in the past decade. The discovery of many extrasolar planets have revealed the existence of exotic planets such as “hot Jupiters” and “eccentric planets,” showing the diversity of planetary systems. Among the discovered extrasolar planets, there are special targets called “transiting planets,” whose orbits seen from the Earth pass in front of the stellar surfaces of their host stars by chance, and these planets provide us precious opportunities for studying extrasolar planets more closely. So far we have pursued two techniques which are only applicable for transiting planetary systems, in order to investigate the environment and the formation process of extrasolar planets. For the purposes, we have conducted spectroscopic observations of transiting planetary systems using the Subaru High Dispersion Spectrograph (HDS). The first study is transmission spectroscopy, a search for atmospheric signatures of transiting planets, targeting one of the brightest transiting planetary system HD 209458. We conducted spectroscopic observations around the transit of HD 209458b. We have developed a high accuracy analysis method for transmission spectroscopy and have applied it for our data. Although we were not able to detect any atmospheric signatures in that system, we obtained the most stringent upper limits as a single night ground-based observation, and we have achieved an enough sensitivity level for detecting possible signatures which some atmospheric models have predicted. The second study is a measurement of the Rossiter-McLaughlin effect in the faint transiting planetary system TrES-1. We observed radial velocities of TrES-1 around the transit phase, and detected the Rossiter-McLaughlin effect which is the radial velocity anomaly due to the partial occultation of the stellar disk during transits. We have placed a constraint on λ, the sky-projected angle between the stellar spin axis and the planetary orbital axis, for TrES-1 by modeling the anomaly. This is the third case for which the angle λ have been measured in transiting planetary systems, and the first demonstration that such measurements are possible for such faint (V ∼ 12) transiting systems. In this thesis, I describe our previous studies above as well as backgrounds and motivation of those studies. I also summarize the observing procedure of the Subaru HDS and analysis methods of observed data, and outline future prospects of studies for transiting planetary systems.