Surface brightness asymmetries (SBA) are a very common feature of stars and result in a difference between the projected barycentre and photocentre. The evolution of those surface features makes this difference time-dependent. In some cases, e.g. for supergiant stars, the displacement can be a non-negligible fraction of the star radius. We investigate the impact of SBA on the Gaia-based astrometric solution and on the data processing flow.
