TY - JOUR

T1 - Rigorous treatment of barycentric stellar motion Perspective and light-time effects in astrometric and radial velocity data

AU - Butkevich, A. G.

AU - Lindegren, Lennart

PY - 2014

Y1 - 2014

N2 - Context. High-precision astrometric and radial-velocity observations require accurate modelling of stellar motions in order to extrapolate measurements over long time intervals, and to detect deviations from uniform motion caused, for example, by unseen companions. Aims. We aim to explore the simplest possible kinematic model of stellar motions, namely that of uniform rectilinear motion relative to the solar system barycentre, in terms of observable quantities including error propagation. Methods. The apparent path equation for uniform rectilinear motion is solved analytically in a classical (special-relativistic) framework, leading to rigorous expressions that relate the (apparent) astrometric parameters and radial velocity to the (true) kinematic parameters of the star in the barycentric reference system. Results. We present rigorous and explicit formulae for the transformation of stellar positions, parallaxes, proper motions, and radial velocities from one epoch to another, assuming uniform rectilinear motion and taking light-time effects into account. The Jacobian matrix of the transformation is also given, allowing accurate and reversible propagation of errors over arbitrary time intervals. The light-time effects are generally very small, but exceed 0.1 mas or 0.1 m s(-1) over 100 yr for at least 33 stars in the Hipparcos catalogue. For high-velocity stars within a few tens of pc from the Sun, light-time effects are generally more important than the effects of the curvature of their orbits in the Galactic potential.

AB - Context. High-precision astrometric and radial-velocity observations require accurate modelling of stellar motions in order to extrapolate measurements over long time intervals, and to detect deviations from uniform motion caused, for example, by unseen companions. Aims. We aim to explore the simplest possible kinematic model of stellar motions, namely that of uniform rectilinear motion relative to the solar system barycentre, in terms of observable quantities including error propagation. Methods. The apparent path equation for uniform rectilinear motion is solved analytically in a classical (special-relativistic) framework, leading to rigorous expressions that relate the (apparent) astrometric parameters and radial velocity to the (true) kinematic parameters of the star in the barycentric reference system. Results. We present rigorous and explicit formulae for the transformation of stellar positions, parallaxes, proper motions, and radial velocities from one epoch to another, assuming uniform rectilinear motion and taking light-time effects into account. The Jacobian matrix of the transformation is also given, allowing accurate and reversible propagation of errors over arbitrary time intervals. The light-time effects are generally very small, but exceed 0.1 mas or 0.1 m s(-1) over 100 yr for at least 33 stars in the Hipparcos catalogue. For high-velocity stars within a few tens of pc from the Sun, light-time effects are generally more important than the effects of the curvature of their orbits in the Galactic potential.

KW - methods: data analysis

KW - technique: radial velocity

KW - astrometry

KW - parallaxes

KW - proper motions

KW - reference systems

U2 - 10.1051/0004-6361/201424483

DO - 10.1051/0004-6361/201424483

M3 - Article

VL - 570

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 1432-0746

M1 - A62

ER -