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

[PPS03-P19] Size distributions of small main belt asteroids obtained by the Subaru/Hyper Suprime-Cam

*Natsuho Maeda¹, Tsuyoshi Terai², Keiji Ohtsuki¹, Fumi Yoshida^3,4, Kosuke Ishihara^2,5,1, Takuto Deyama^6,1 (1.Graduate school of science, Kobe University , 2.National Astronomical Observatory of Japan, 3.Chiba Institute of Technology, 4.University of Occupational and Environmental Health, 5.The Graduate University for Advanced Studies, 6.NTT Data MSE Corporation)

Keywords:asteroids, size distribution, observation

The size distribution of asteroids provides us with information to reveal their formation and evolution. Thus, it is important to obtain an accurate size distribution of asteroids by observation. Previous observational studies showed that the size distribution of main-belt asteroids has a bend around 1 km, and the power-law index below ~1 km in diameter is smaller than the larger size range (Jedicke et al. 2015 for a review). However, some previous observational works have problems with the number of asteroid samples used and insufficient correction for decreasing source detection efficiency as the source fades (Ivezić et al. 2001; Gladman et al. 2009). The size distribution of faint main-belt asteroids needs to be re-examined using a homogenous large statistical sample and accurate correction.
We performed a survey observation of small main-belt asteroids with Hyper Suprime-Cam, a wide-field camera installed on the 8.2 m Subaru Telescope (Maeda et al. 2021). We detected more than 3000 main-belt asteroids with a detection limit of 24.2 mag in the r-band. To remove a detection bias, we selected a statistical sample with absolute magnitude brighter than 20.3 mag and corrected the number of asteroids in each bin of the size distribution using the detection efficiency examined for each CCD image.
We obtained the size distribution of main-belt asteroids larger than 0.4 km in diameter, combining the size distributions of our work with previous works for larger bodies. We found that the total number of main-belt asteroids larger than 0.4 km in diameter is estimated to be 8.6×10⁶. This is a couple of times as large as that obtained by extrapolating the results of previous works (Ivezić et al. 2001; Gladman et al. 2009). This result shows the high sensitivity of the Subaru/HSC allowed a high collection rate for faint objects. It also shows that accurate number correction is necessary, taking into account the detection efficiency of each CCD image.