[P-PS02] [EE] Small Bodies: Exploration of the Asteroid Belt and the Solar System at Large

[PPS02-P04] Kilometer-sized trans-Neptunian objects revealed by OASES

*有松 亘¹、津村 耕司²、市川 幸平¹、臼井 文彦³、大坪 貴文⁴、小谷 隆行¹、 猿楽 祐樹⁴、和田 武彦⁵、長勢 晃一⁵、渡部 潤一¹ (1.国立天文台、2.東北大学　学際科学フロンティア研究所、3.神戸大学大学院 理学研究科 惑星科学研究センター、4.東京大学、5.宇宙航空研究開発機構　宇宙科学研究所)

Organized Autotelescopes for Serendipitous Event Survey (OASES) is an optical observation project that aims to detect and investigate stellar occultation events by kilometer-sized trans-Neptunian objects (TNOs). The abundance and the size distribution of the kilometer-sized TNOs is thought to provide fundamental knowledge of the accretion processes from the early stages of the outer solar system. However, they are extremely faint and are impossible to detect directly even with 8-m~10-m aperture telescopes. Instead of the direct detection, a monitoring observation of stellar occultation events is one of the possible ways to estimate the abundance and the size distributions of the kilometer-sized TNOs. Since stellar occultations by the TNOs are very rare (lower event rate than 10^-2 events per year per star) and short duration (shorter than one second) events, a lot of stars must be monitored simultaneously with a sampling cadence much higher than general optical observation instruments. We thus developed multiple low-cost observation systems for wide-field and high-speed photometry. The observation system consists of commercial off-the-shelf 0.28 m aperture f/1.58 optics providing a 2.3 × 1.8 square-degree field of view and a commercial CMOS camera obtaining full-frame imaging with a frame rate greater than 10 Hz. This project currently exploits two observation systems, which are installed in Miyako island, Okinawa, Japan. Owing to the recent improving CMOS technology of high-speed imaging and low readout noise, the observation system is capable of monitoring ∼ 2000 stars at the Galactic plane simultaneously with V-band magnitudes down to ∼ 13.0, providing ∼20% photometric precisions in light curves with a sampling cadence of 15.4 Hz. The OASES two observation systems are therefore executing coordinated monitoring observations of a dense stellar field in order to detect the occultations by the kilometer-sized TNOs for the first time.