Secular aberration drift in stellar proper motions and their implication on the stellar reference frame

Abstract

The motion of the Solar System barycenter (SSB), which is the spatial origin of the International Celestial Reference System, causes a directional displacement known as secular aberration. The secular aberration drift caused by the galactocentric acceleration of the SSB has been modeled in the third generation of the International Celestial Reference Frame. In this talk, we will address another secular aberration drift effect, which is due to the change in the line-of-sight direction, and study its implications for stellar proper motions. To this end, we derived a complete formula for the secular aberration drift and computed its influence on stellar proper motion based on the astrometric data in Gaia Data Release 3. We found that the secular aberration drift due to the change in the line-of-sight direction tended to decrease the observed proper motions for stars with galactic longitudes between 0 and 180 degrees, and increase the observed proper motion for stars in the remaining region. If this secular aberration drift effect is ignored, it will induce an additional proper motion of > Imas yr-1 for 84 stars and > 0.02 mas yr-1 for 5 944 879 stars, which is comparable to or several times greater than the typical formal uncertainty of the Gaia proper motion measurements at G < 13. Furthermore, we used the intermediate astrometric data from the Hipparcos- 2 catalogue to study the implication of ignoring the secular aberration drift on the determination of stellar trigonometric parallaxes. We recommend that the secular aberration drift due to the change in the line-of-sight direction and the acceleration of the SSB should be modeled to make the stellar reference frame.