Aberration in proper motions for stars in our Galaxy

TL;DR

This paper extends previous work on aberration in proper motions caused by accelerations in the Milky Way, quantifying its magnitude near the Galactic center and discussing its implications for high-precision astrometry like Gaia.

Contribution

It provides new estimates of aberrational proper motions using different Galactic rotation models and evaluates their impact on stellar orbit determination.

Findings

Aberration can reach over 1000 uas/yr near the Galactic center with a flat rotation curve.

More realistic rotation curves limit aberrational proper motions to about 150 uas/yr.

Aberration effects are small but significant for future high-precision astrometry.

Abstract

Accelerations of both the solar system barycenter (SSB) and stars in the Milky Way cause a systematic observational effect on the stellar proper motions, which was first studied in the early 1990s and developed by J. Kovalevsky (aberration in proper motions, 2003, A&A, 404, 743). This paper intends to extend that work and aims to estimate the magnitude and significance of the aberration in proper motions of stars, especially in the region near the Galactic center. We adopt two models for the Galactic rotation curve to evaluate the aberrational effect on the Galactic plane. Based on the theoretical developments, we show that the effect of aberration in proper motions depends on the galactocentric distance of stars; it is dominated by the acceleration of stars in the central region of the Galaxy. Within 200 pc from the Galactic center, the systematic proper motion can reach an amplitude larger than 1000 uas/yr by applying a flat rotation curve. With a more realistic rotation curve which is linearly rising in the core region of the Galaxy, the aberrational proper motions are limited up to about 150 uas/yr. Then we investigate the applicability of the theoretical expressions concerning the aberrational proper motions, especially for those stars with short period orbits. If the orbital period of stars is only a fraction of the light time from the star to the SSB, the expression proposed by Kovalevsky is not appropriate. With a more suitable formulation, we found that the aberration has no effect on the determination of the stellar orbits on the celestial sphere. The aberrational effect under consideration is small but not negligible with high-accurate astrometry in the future, particularly in constructing the Gaia celestial reference system realized by Galactic stars.