Photometric characterization of near-Earth objects from OASI and CASLEO observations

ABSTRACT We present the photometric characterization of 39 NEOs observed between 2021 and 2024 using telescopes at the Observatório Astronômico do Sertão de Itaparica (OASI, Brazil) and the Complejo Astronómico El Leoncito (CASLEO, Argentina), as part of the IMPACTON project. This study combines rotational light curve, solar phase curve, and multiband photometry to determine key physical parameters, including rotation period, colour indices, taxonomic classification, absolute magnitude, and phase-function parameters. Rotation periods were determined for 26 NEOs, ranging from 2.33 to 19.81 h, with a mean value of $5.13 \pm 3.63$ h. Some objects exhibit rotation near the spin barrier, suggesting possible cohesion or binarity. Taxonomic classification was performed for 34 NEOs, showing a predominance of the S/Q-complex (50 per cent), followed by the C-complex (23.5 per cent). A catalogue of 2459 NEOs with published taxonomic data was compiled to analyse compositional trends with diameter. The S/Q-complex remains dominant across all size ranges, while the relative abundance of C-complex asteroids increases with size. For 13 targets, phase-function parameters were robustly estimated, corrected for rotational effects. In the $G_1$–$G_2$ space, only six objects follow the expected taxonomic trends, while most deviate, indicating possibly distinct surface properties from larger main-belt asteroids. Complete photometric characterization was achieved for 11 NEOs. These findings highlight the importance of systematic photometric surveys of small NEOs, not only for expanding the catalogue of characterized objects and to uncover trends that might inform on the origin and evolution of the smallest members among the Solar system’s small bodies.