SpinTrace: A Python Library to Study the Physical Properties of Small Bodies Using Survey-based Photometry

Abstract We present S pin T race , a Python tool developed to retrieve and process survey-based photometry for the detection of brightness variations—primarily, but not exclusively—due to asteroid rotation. Current implementation features a modular pipeline for downloading, calibrating, and analyzing point-spread function photometry from the Zwicky Transient Facility (ZTF), with support for phase curve modeling and periodicity searches, either across the entire dataset or within subsamples. It also uses parallelized downloading and local caching to improve performance. We applied S pin T race to two well-studied small bodies: the trans-Neptunian object and dwarf planet (136108) Haumea and the large Jupiter Trojan (624) Hektor. For Haumea, we obtained absolute magnitudes in each of the three Sloan Digital Sky Survey filters available within the ZTF survey, confirmed its rotational period of P = 3.915343 ± 0.00005 hr, and saw evidence of Hi’iaka’s mutual orbit. Hektor is known for its elongated shape and exhibits significant changes in the amplitude of its rotational light curve over the ZTF time span. To display this variability, after obtaining the rotational period of P = 6.92025 ± 0.00027 hr, the dataset was divided into subsamples and individually analyzed. We recovered rotational light curves with amplitudes varying from 0.092 ± 0.028 mag in 2018, peaking at 1.135 ± 0.057 mag in 2021, and again decreasing to 0.070 ± 0.028 mag in 2025. S pin T race was designed in preparation for the upcoming 10 yr Legacy Survey of Space and Time conducted by the Vera Rubin Observatory, which is expected to yield thousands of multifilter photometric measurements per object annually.