Secular aberration drift in stellar proper motions: An additional term due to the change in line-of-sight direction

TL;DR

This paper derives a complete formula for secular aberration drift caused by the change in line-of-sight direction and assesses its impact on stellar proper motions using Gaia DR3 data, highlighting the importance of modeling this effect for accurate celestial reference frames.

Contribution

It introduces a new comprehensive model for secular aberration drift due to line-of-sight changes and evaluates its significance on Gaia proper motion measurements.

Findings

The drift affects proper motions differently depending on galactic longitude.

Ignoring this effect can cause significant errors in stellar proper motion measurements.

The effect is comparable to or exceeds Gaia's measurement uncertainties for many stars.

Abstract

The motion of the barycenter of the Solar System (SSB), the 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. We aim to address another secular aberration drift effect due to the change in the line-of-sight direction and study its implications for stellar proper motions. A complete formula of secular aberration drift is derived, and its influence on stellar proper motion is computed based on the astrometric data in \textit{Gaia} Data Release 3. We found that the secular aberration drift due to the change in the line-of-sight direction tends to decrease the observed proper motions for stars with galactic longitudes between $0^{\circ}$ and $180^{\circ}$, 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 $>1\,\mathrm{mas\,yr^{-1}}$ for 84 stars and $>0.02\,\mathrm{mas\,yr^{-1}}$ for 5\,944\,879 stars, which is comparable to or several times greater than the typical formal uncertainty of the \textit{Gaia} proper motion measurements at $G<13$. 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 consistent with the extragalactic reference frame.