Origin of the discrepancy between Hubble and ground-based absolute magnitudes

Determine whether the approximately 0.25-magnitude difference between Bennu’s Hubble-derived absolute magnitudes and the earlier ground-based measurement is caused by uncertainty in Bennu’s phase function or by a color term in converting F350LP measurements to the V filter.

Background

The Hubble observations yielded absolute magnitudes approximately 0.25 magnitudes brighter than an earlier ground-based value, while remaining consistent with a later updated ground-based estimate. The conversion from the broad F350LP passband to the V band and the adopted phase-function correction both introduce systematic uncertainties.

The paper does not resolve whether the discrepancy is attributable to phase-function uncertainty or to a color-dependent photometric calibration effect. Establishing the source of this difference would improve the consistency of Bennu’s long-term photometric record and the interpretation of its brightness measurements.