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

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 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 ± 0.002 s for 2021 TY 14 , 21.099 ± 0.003 s for 2021 UW 1 , and 8.779 ± 0.013 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 ∼20% in composition cannot be ruled out. Our study demonstrates that high-cadence, multicolor photometry with small to medium telescopes is effective for determining rotation periods and broadly classifying the spectral properties of tiny NEAs.