Organized autotelescopes for serendipitous event survey (OASES): Design and performance

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). In this project, multiple low-cost observation systems for wide-field and high-speed photometry were developed in order to detect rare and short-timescale stellar occultation events. The observation system consists of commercial off-the-shelf 0.28 m aperture f/1.58 optics providing a 2^◦.3 × 1^◦.8 field of view. A commercial CMOS camera is coupled to the optics to obtain full-frame imaging with a frame rate greater than 10 Hz. As of 2016 September, this project exploits two observation systems, which are installed on Miyako Island, Okinawa, Japan. Recent improvements in CMOS technology in terms of high-speed imaging and low readout noise mean that the observation systems are capable of monitoring ∼2000 stars in the Galactic plane simultaneously with magnitudes down to V ∼ 13.0, providing ∼20% photometric precision in light curves with a sampling cadence of 15.4 Hz. This number of monitored stars is larger than for any other existing instruments for coordinated occultation surveys. In addition, a precise time synchronization method needed for simultaneous occultation detection is developed using faint meteors. The two OASES observation systems are executing coordinated monitoring observations of a dense stellar field in order to detect occultations by kilometer-sized TNOs for the first time.