Relative Motion in the Hierarchical Triple System ADS48 on the Basis of Gaia DR2 and 26-Inch Refractor of Pulkovo Observatory Data

Abstract—According to the exact positions and proper motions of the three components of the star ADS48 from Gaia DR2, their parallax and radial velocities for the epoch 2015.5 the instantaneous relative positions and motions of the components were determined. Only from the Gaia DR2 observations, the family of orbits of the AB pair was calculated by the method of apparent motion parameters, from which those that best agree with the Pulkovo data were selected. Comparison with the first observations of the 19th century made it possible to independently estimate the sum of the masses of the components in the range 1.15 < M_{A + B} < 1.4 M_⊙. The orbits of the outer pair were calculated: with a minimum period of 79 × 10³ years and the most probable one—about 3 × 10⁵ years. It is concluded that the system is stable for the most probable value of the relative− radial velocity ∆V_r = 0.7 km s^–1 and may be unstable near the boundaries of the possible velocity difference. A detailed analysis of homogeneous Pulkovo observations revealed a disturbance with a period of 11 years. It is shown that this disturbance is associated not with a star, but with a periodic climatic process that changes the observation conditions. Comparison of instantaneous and average relative motion does not exclude the presence of a planetary mass satellite in one of the components.