On the implications of the Galactic aberration in proper motions for celestial reference frame

TL;DR

The paper assesses the galactic aberration in proper motions, concluding it is a minor correction for high-precision astrometry and discussing its implications for celestial reference frame modeling.

Contribution

It demonstrates that the galactic aberration correction can be accurately computed with current knowledge and argues for reverting to classical astrometric models in VLBI data analysis.

Findings

GA correction accuracy is better than 10% with current parameters.

Remaining GA effect is negligible at current measurement precision.

Revising VLBI models impacts radio source position estimates by tens of microarcseconds.

Abstract

During the last years, much attention has been paid to the astrometric implications of the galactic aberration in proper motions (GA). This effect causes systematic errors in astrometric measurements at a microarcsecond level. Some authors consider it so serious that it requires redefinition of the celestial reference system (CRF). We argue that such attention to the GA is too much exaggerated. It is just a small astrometric correction that must be taken into account during highly accurate astrometric and geodetic data processing. The accuracy of this correction depends on accuracy of the Galactic rotation parameters and, for most application, on the accuracy of the rotation matrix between Galactic and equatorial systems. Our analysis has shown that our today knowledge of these two factors is sufficient to compute the GA correction with accuracy of better than 10%. The remaining effect at a level of few tenths microarcsecond/yr is negligible nowadays. Another consequence of introducing the GA correction is necessity to return to classical astrometric modeling of the VLBI-derived extragalactic radio source position by the linear trend model. Changing the current paradigm of VLBI-derived CRF based on assumption of zero motion of radio sources to classical one leads to bias in the radio source positions up to several tens microarcseconds for catalog at epoch J2000.0.