Star catalog position and proper motion corrections in asteroid astrometry II: The Gaia era

Astrometric positions of moving objects in the Solar System have been measured using a variety of star catalogs in the past. Previous work has shown that systematic errors in star catalogs can affect the accuracy of astrometric observations. That, in turn, can influence the resulting orbit fits for minor planets. In order to quantify these systematic errors, we compare the positions and proper motion of stellar sources in the most utilized star catalogs to the second release of the Gaia star catalog. The accuracy of Gaia astrometry allows us to unambiguously identify local biases and derive a scheme that can be used to correct past astrometric observations of solar system objects. Here, we provide substantially improved debiasing tables for 26 astrometric catalogs that were extensively used in minor planet astrometry. Revised corrections near the galactic center eliminate artifacts that could be traced back to reference catalogs used in previous debiasing schemes. Median differences in stellar positions between catalogs now tend to be on the order of several tens of milliarcseconds (mas) but can be as large as 175 mas. Median stellar proper motion corrections scatter around 0.3 mas/yr and range from 1to 4 mas/yr for star catalogs with and without proper motion, respectively. The tables presented in this work contain a posteriori corrections meant to improve orbit fits based on optical observations that were measured against astrometric catalogs other than Gaia. However, astrometrists are strongly encouraged to make use of the most recent Gaia astrometric catalog when submitting new observations.

Since previous debiasing schemes already reduced systematics in past observations to a large extent, corrections beyond the current work may not be needed in the foreseeable future.