Minor planet astrophotometry

Abstract

Historically, the Minor Planet Center (MPC) has concentrated on improving the quality of the astrometric observations and the resulting orbits of minor planets. In light of long-standing complaints in the literature about the quality of the photometric parameters for the minor planets, there has been a need to improve the quality of the absolute magnitudes, H, and slope parameters, G. However, this task is complex, as the bulk of the minor-planet magnitude estimates are suppl ied by the astrometric observers. These observations are not made through standard fillers and are made with respect to the (indifferent) magnitudes in numerous astrometric reference catalogues. Such magnitude estimates are labelled astrophotometry, to reflect their low quality. This thesis describes a method for correcting the catalogue- and observer-specific errors present in the astrophotometry. This method was applied to more than 70 million astrometric observations with magnitude estimates. New H determinations have been made for 322 607 numbered minor planets, while new G determinations have been made for 64 348 numbered minor planets. New assumed G values have been determined for 258 259 numbered minor planets. Analysis of the results shows that the problems identified in the literature have been removed, particularly the -0.5 magnitude offset at H≈14 that is present in the current MPC HG data set. Implications of the new H magnitudes on the albedos determined by the WISE space mission and on the differential H distributions of various types of solar-system object are discussed.