Light deflection in binary stars

Abstract

The light deflection of one component of a binary system due to the gravitational field of the other component is investigated. While this relativistic effect has not been observed thus far, the question arises of whether this effect can become detectable in view of today's high-precision astrometry, which soon will reach the microarcsecond level of accuracy. The effect is studied and its observability is investigated. It turns out that in total there are about 10 3 binaries having orbital parameters such that the light deflection amounts to at least 1 μas. Two stringent criteria for the orbital parameters are presented, by means of which one can easily determine the maximal value of light deflection effect for a given binary system. It is found that for relevant binaries their orbital parameters must take rather extreme values in order to have a light deflection of the order of a few microarcseconds. Only in a very few and rather extreme binary systems might the light deflection effect be detectable by today's astrometry, but their existence is highly improbable. Thus, the detection of this subtle effect of relativity still remains a challenge for future astrometric missions. © © 2012. The American Astronomical Society. All rights reserved.