Extra-solar planet search using the Subaru Telescope

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This research program aims to observe one hundred young stars in order to detect their circumstellar structures and planet candidates with CIAO, a Subaru Telescope coronagraphic imager which started its operation early among the large optical-infrared telescopes in the world. We have imaged about 80 young stars for the last three years, now analyzing the data in detail. The followings are the two major results that we have achieved so far.(1)Detection of Spiral Structure in the Protoplanetary Disk around AB AurigaeA prominent spiral structure was for the first time discovered in the protoplanetary disk around the young star AB Aurigae. In the primordial solar nebula, planet formation begins with the accumulation of dust particles into planetesimals, followed by their collision and coalescence to form protoplanets, which may grow up to giant gas planets if they become sufficiently heavy to attract ambient gas. Protoplanetary disks within which the similar planet formation process is bel … More ieved to occur should have masses of order 1% of their central stars and be gravitationally stable. Protoplanetary disks are thus so far believed to have no structure such as spirals caused by gravitational instability. The spiral structure suggests that the protoplanetary disk around AB Aurigae might be heavy to maintain spiral instability. Such a heavy disk might fragment and follow a different path of planet formation than that occurred in our solar system.(2)Discovery of a 40 Juniter Mass Companion to DH TauriWe have detected 20 companion candidates among the observed young stars and are making follow up observations to judge whether or not they are real physical companions. During this process we have found that one star located close to DH Tauri is a physical companion with a 40 Jupiter masses or a 0.04 solar masses. Because planets are for the moment defined as companions with masses less than 13 Jupiter masses, our discovery means that direct imaging of planets is almost at hand now. Less