Determination of the Rotation Period of the Asteroid Amphitrite Using Observational Data from the Itera Robotic Telescope

Abstract

Asteroid (29) Amphitrite is an S-type asteroid in the main belt with a complex light curve caused by its rotation, and this study aims to determine its rotation period. Multifilter photometric observations (B, V, R) were conducted over three nights (May 1, 5, and 8, 2026) at the Itera Lampung Astronomy Observatory (OAIL) using the ITERA Robotic Telescope (IRT). The data were processed through image reduction, astrometry, and differential photometry, and then analyzed using the Lomb-Scargle periodogram, bootstrap, and fourth-order Fourier fitting. Asteroid (29) Amphitrite was found to have an apparent magnitude ranging from 9.8 to 11.6 mag. Integrating the analysis results from the three spectral filters yields a range for Amphitrite’s rotation period (29) between 5.82 and 6.03 hours, specifically 5.8596 ± 0.4666 hours for filter B (RMS fit 0.02953); 5.8246 ± 0.3452 hours for filter V (RMS fit 0.03779); and the best estimate of 6.0254 ± 0.254 hours with the smallest RMS fit value of 0.02385 for filter R. The weighted average rotation period obtained was 5.94046 ± 0.18848 hours, deviating by about 10% from the reference value (5.39 ± 0.0007 hours). The derived rotation period deviates by approximately 2.9σ from the literature value, which may be attributed to the limited phase coverage and potential aliasing effects in the observational data . This study demonstrates that photometric observations using a medium-sized robotic telescope can provide estimates of an asteroid’s rotation period, although the precision is still influenced by the coverage and quality of the observational data. Meanwhile, variations in the asteroid’s surface composition still require further investigation through color index analysis.