Aperture photometry on asteroid trails

Abstract

Context. Near-Earth objects (NEOs) on an impact course with Earth can move at high angular speeds. Understanding their properties, including their rotation state, is crucial for assessing impact risks and mitigation strategies. Traditional photometric methods face challenges in accurately collecting data on fast-moving NEOs. Aims. This study introduces an innovative approach to aperture photometry, tailored to analyzing trailed images of fast-moving NEOs. Our primary aim is to extract rotation state information for fast rotators. Methods. We applied our approach to the trailed images of three asteroids: 2023 CX1, 2024 BX1, and 2024 EF, which were either on a collision course or on a close fly-by with Earth, resulting in high angular velocities. By adjusting the aperture size, we controlled the effective instantaneous exposure time of the asteroid to increase the sampling rate of photometric variations. This enabled us to detect short rotation periods that would be challenging to derive with conventional methods. Results. Our analysis shows that trailed photometry significantly reduces the overhead time associated with CCD readout, enhancing the sampling rate of the photometric variations. We demonstrate that this technique is particularly effective for fast-moving objects, providing reliable photometric data when the object is at its brightest and closest to Earth. For asteroid 2024 BX1, we detect a rotation period of 2.5888 ± 0.0002 seconds, the shortest ever recorded. We discuss under what circumstances it is most efficient to use trailed observations coupled with aperture photometry for studying the rotation characteristics of NEOs.