Simultaneous Tricolor Video Observations of Three Tiny Near-Earth Asteroids with Sub-Minute Rotation Periods

Abstract

Studying the physical properties of near-Earth asteroids (NEAs) is crucial for understanding their dynamical histories and origins, and assessing impact hazards to Earth. Tiny NEAs with diameters smaller than 100 m are intrinsically faint and are typically observable only during close approaches, resulting in few well-characterized objects. Furthermore, because these objects are often fast-moving and fast-rotating, sequential multiband photometry is prone to systematic offsets in derived colors. To mitigate this effect, we performed simultaneous $g$-, $r$-, and $i$-band photometry of three tiny NEAs using the TriColor CMOS Camera and Spectrograph (TriCCS) on the 3.8 m Seimei Telescope. We used high-cadence video observations with exposure times of 1 s and 5 s to investigate lightcurve variations on timescales of seconds. All three NEAs are confirmed as fast rotators with rotation periods shorter than 60 s: $15.281\pm0.002$ s for 2021 TY$_{14}$, $21.099\pm0.003$ s for 2021 UW$_{1}$, and $8.779\pm0.013$ s for 2022 GQ$_{1}$. The derived colors indicate that 2021 TY$_{14}$ belongs to the X-complex, while 2021 UW$_{1}$ and 2022 GQ$_{1}$ belong to the S-complex. Their positions in the diameter--rotation period diagram show that all three objects belong to the small, fast-rotating NEA population, with 2022 GQ$_{1}$ being the smallest and fastest-rotating among them with spectroscopic measurements. Analysis of the color time series suggests that the surfaces of observed NEAs are largely homogeneous, although 2021 TY$_{14}$ exhibits statistically significant $g-r$ color heterogeneity with a projected spot fraction of approximately 50%. For 2021 UW$_{1}$, minor localized variations of up to $\sim20$% in composition cannot be ruled out.