Debiasing astro-Photometric Observations with Corrections Using Statistics (DePhOCUS)

The photometry of optical observations of asteroids received and distributed by the Minor Planet Center (MPC), also known as astro-photometric observations, often serve as the only available basis for the derivation of physical properties such as the absolute magnitude, which is a proxy to infer the size of the observed object, and its albedo with thermal observations. Magnitude information is acquired in different color bands, with respect to reference star catalogs, and from different observatory sites. In order to combine measurements, photometry using different bands need to be converted to a common band, typically V-band. Current band correction schemes in use by IAU’s MPC, JPL’s Center for NEO Studies (CNEOS) and ESA’s NEO Coordination Centre (NEOCC) use average correction values for the apparent magnitude derived from photometry of asteroids. By analyzing the photometric residuals of asteroids, we refine the previous correction scheme and additionally debias the observations based on their catalog and observatory. We describe a new statistical photometry correction scheme for asteroid observations with debiased corrections. Testing this scheme on a reference group of asteroids, we see a 51% reduction in the photometric residuals. Moreover, the new scheme leads to a more accurate and debiased determination of the H-G magnitude system and, in turn, leading to a more reliable inferred size, which is highly needed for asteroid population models. We discuss the significant shift in the corrections with this "DePhOCUS" debiasing system, its limitations, and the impact for photometric and physical properties of all asteroids, especially near-Earth objects (NEOs).