Gaia vs Hipparcos: the Accuracy of Parallax Measurements

Abstract

We present a solution for the problem of the discrepancy in the measured trigonometric parallaxes for the stellar binary system HIP 84092. To solve the discrepancy, we used the orbital parameters and our method for analyzing binary and multiple stellar systems (BMSSs)s, described by \mbox{Al-Wardat} in 2002. We used all the available parallax measurements from Gaia DR3, DR2 and Hipparcos-2 in estimating the fundamental parameters of the individual components of the system. Such measurements are usually affected by the orbital motion of the components and the shift of the system photocenter. The masses estimated using the Al-Wardat method along with the modified orbital elements lead to a new dynamical parallax for the system $\pi_{Dyn}=8.24\pm0.15$~mas, which lies in between the measurements of Hipparcos-2 ($8.29 \pm 0.97$ mas) and Gaia DR3 ($8.4806 \pm 0.4863$ mas), while the parallax from Gaia DR2 ($20.0561 \pm 1.1615$ mas) is far from being accurate. This can be explained by the fact that the Gaia telescope has a higher resolution than that of Hipparcos. Based on the fundamental parameters of the binary system components and their positions on the evolutionary tracks, we conclude that the system consists of A7.5 and F1 solar-metalicity main-sequence stars with an age of 0.708 Gyr. Fragmentation is proposed as the most likely scenario for the formation and evolution of the system.