Trigonometric parallax discrepancies in space telescopes measurements I: The case of the stellar binary system Hip 84976

In addition to the complete set of fundamental parameters of its individual components, we present the solution for the discrepancy between the two main astrometric space telescopes Gaia and Hipparcos, in their measurements of the trigonometric parallax for the stel-lar binary system Hip 84976. In our analysis of the system, we followed Al-Wardat's method for analyzing binary and multiple stellar systems along with Tokovinin's dynamical method. Using these two methods, we estimated the system's atmospheric, dynamical, and geometrical parameters including the individual masses. The estimated masses and the modified orbital elements were used to give a new dynamical parallax for the system as (pDyn = 11.48 +/- 0.45 mas), which lies between the measurements given by the old (9.01 +/- 1.22 mas) and the new (11.80 +/- 1.23 mas) Hipparcos catalogs. It also shows that Hipparcos 2's (2007) parallax measurement is more accurate than that given by Gaia DR3 (12.5899 +/- 0.3496 mas) for this system, while that given by Gaia DR2 (24.1841 +/- 1.8560 mas) is far from accurate. The results were used to put the two components of the system on the right positions on the H-R diagram, evolutionary tracks, and isochrones, and proposed that the system was formed by fragmentation 1.99 Gyr ago. (c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.