Speaker
Description
The absolute magnitude H of asteroids is a fundamental property.
It is a proxy to diameter, it is required to predict apparent magnitude, and it is the only way to measure colors whenever filters are not observed (near-)simultaneously.
Major ephemerides computation centers like the Minor Planet Center (MPC), the Jet Propulsion Laboratory (JPL), the Asteroid Dynamical Site (AstDyS), and the ESA near-Earth Objects coordination center (NEOCC) provide the absolute magnitude of each asteroid, computed together with its osculating elements. These centers use the HG'' model by Bowell (1989) to determine the absolute magnitude from the evolution of photometry against the phase angle.
This model has clear limitations at small and large phase angles and has been superseded by theHG1G2'' model by Muinonen et al. (2010).
However, none of these models account for the constant changing geometry
of asteroids, which shapes are not spherical. This has been reported by many authors,
as the analysis of different apparitions of the same asteroid may not provide consistent
absolute magnitudes. Jackson et al. (2022) even recently showed how this affects near-Earth asteroids over a single apparition.
We have recently developed a new model for phase curves, dubbed sHG1G2'', and implemented it within the FINK broker of alerts designed for LSST (Moller et al.
2021). This new model accounts for the changing geometry without adding much complexity, hence without requiring large datasets. It provides are more robust determination of the absolute magnitude, together with the orientation and oblateness of the targets (Carry et al. 2024). After summarizing open issues in the current determination of absolute magnitudes, I will present thesHG1G2'' model and the results already achieved using ZTF photometry.
