DETERMINATION OF THE ROTATION PERIOD OF ASTEROIDS FROM A SHORT SERIES OF BRIGHTNESS OBSERVATIONS UNEVENLY SPREAD OVER A LONG TIME INTERVAL

The main belt asteroids, situated between two planets (Jupiter and Mars), are subject to a significant influence from these planets (Mars-crossers by Mars), as well as from other planets. This is particularly concerning in the case of asteroids with small asteroid-Earth minimum orbit intersection distances (MOIDs), as these have the potential to pose a significant hazard to Earth. In this study, we present light curves for 15 main belt and Mars-crossing asteroids with small asteroid-Earth MOIDs, which are smaller than 1.1 AU. These asteroids are particularly likely to become Earth-crossing or near-Earth asteroids. In order to obtain brightness measurements, photometry was performed using CCD images captured by the Baldones Schmit telescope (1.2-metre mirror, equipped with two STX-16803 CCDs). The light curves were obtained by comparing the brightness of the asteroids with the Sun-like colour index of five to six stars, processed with MaxIm DL. The remaining brightness measurements are derived from the Minor Planet Center (MPC) database, based on data from 18 observatories and the Transiting Exoplanet Survey Satellite (TESS). The brightness measurements are only complementary to the asteroid position measurements. Therefore, these brightness measurements are typically not very precise and are separated by different time intervals that may be quite extensive. In order to find the asteroid rotation period, it is sometimes necessary to employ data correction as well as programs that are able to identify the period in unevenly scattered data. Our analysis employed the Lomb–Scargle method, which identified period values for 14 of the asteroids. The method can be used to obtain results for the simple rotations of asteroids, provided that the asteroids are observed in phases within the range of 7 and 40 degrees, that their shape is nearly an elongated ellipsoid, and that their rotation axes are almost perpendicular to their heliocentric orbital planes.