[P-PS03] Small Solar System Bodies: Latest results and new perspectives on the Solar System evolution

[PPS03-19] ASTEROID DETECTION APPLICATION "COIAS" FOR THE SUBARU HSC ARCHIVE DATA

*Seitaro Urakawa¹, Keisuke Sugiura², Natsuho Maeda³, Takafumi Ootsubo⁴, Yohei Moteki⁶, Daisuke Kinoshita⁷, Kohei Kitazato⁵, Tomohiko Sekiguchi⁸, Michitaro Koike⁴, Kumiko Usuda-Sato⁴ (1.Japan Spaceguard Association, 2.Tokyo Institute of Technology, 3.Kobe University, 4.National Astronomical Observatory of Japan, 5.The University of Aizu, 6.Hokkaido University, 7.National Central of University, 8.Hokkaido University of Education)

Keywords:Asteroids, Planetary Defense, Subaru Telescope, Archive Science

We report the development of the asteroid detection application COIAS (Come On! Impacting ASteroids) for the Subaru telescope HSC (Hyper Suprime-Cam). More than a million asteroids have been discovered since the discovery of Ceres in 1801. In 1918, the concept of “asteroid family” is suggested from the orbital distribution of known 940 asteroids at that time (Hirayama 1918)[1]. The asteroid family is a population of asteroids that share similar orbital elements. The members of families are thought to be collisional fragments that were produced by the impact event on the parent asteroid. The orbital distribution of asteroid families broadens in time due to the variety of escape velocity of collisional fragments, and the Yarkovsky effect (Vokrouhlický et al. 2006)[2]. The Yarkovsky effect is particularly prominent for asteroids with diameters smaller than 300 m. Moreover, a mechanism of orbital evolution from main-belt asteroids (MBAs) to near-Earth objects (NEOs) is thought to be the injection of asteroids to the orbital resonance. Asteroids smaller than 300m in diameter are subject to the Yarkovsky effect and is likely to move into the orbital resonance. Therefore, the information of orbital distribution for asteroids with diameters smaller than 300 m has importance to make clarify the broaden mechanism of asteroid families and the orbital evolution from MBAs to NEOs. However, most of the discovered asteroids in the main-belt region have diameters larger than 1 km. The orbital distributions of asteroids cover the range of 300 m in diameter have not been clarified. The aim of our study cataloged the orbital elements of 300 m-sized asteroids using Subaru HSC archive data. HSC is a super wide field camera mounted with the prime focus of 8.2 m Subaru telescope. The field of view covers the area of 1.5 deg in diameter by 104 CCD chips. All the HSC data are archived and opened a year and a half later from the observations. A large number of asteroids with diameters smaller than 300 m will be imaged in such an archived data. However, the coordination and brightness of these asteroids were not reported effectively to the Minor Planet Center (MPC). The reason is thought to be that there was no useful application system which can conduct the detection, measuring coordinates, photometry, and reporting to the MPC. Developments of the smooth detection and report system are required for asteroids that are imaged by the Subaru HSC. In order to solve the problems, we developed “COIAS” which is an application system for detecting, measuring coordinates, photometry, and reporting to the MPC about asteroids imaged in the HSC. One of the problems for detecting moving objects distinguishes between noise and asteroids. COIAS removes the false detection in visual way using the Graphical User Interface (GUI). The detection of moving objects by machine learning algorithm was considered for the Subaru HSC (Lin et al. 2018)[3]. However, the HSC data were obtained under a variety of conditions, such as exposure time, filter, and survey area. The machine learning algorithms are difficult to be applied for the variety of conditions. Thus, we decided that the visual inspection is better than machine learning algorithms in the current situation. When we performed an asteroid detection test using COIAS, 6367 unknown asteroids are detected by one night’s ecliptic plane survey. The estimated number of unknown asteroids reaches tens of thousands if we use COIAS for all the HSC archive data. The tentative orbital calculation by the one night’s observation arc indicated that a few percent of 6367 unknown asteroids are near-earth objects (NEOs). COIAS can play an important role in the planetary defense. Moreover, the GUI operation of COIAS gives the experience of asteroid detection to students and citizen people. The detection of unknown asteroids by COIAS is expected to have an educational effect on students and to contribute to citizen astronomy. [References][1]Hirayama, K., 1918, AJ, 31, 185, [2]Vokrouhlický, D., Brož, M., Bottke, W. F., Nesvorný, D., and Morbidelli, A., 2006, Icarus, 182, 118, [3]Lin, H-W., Chen, Y-T., Wang, J-H., Wang, S-Y., Yoshida, F., Ip, W-H., Miyazaki, S., and Terai, T., 2018, PASJ, 70, 39