# Relative orbit orientation in several resolved multiple systems

## TL;DR

This study improves understanding of multiple star systems by accurately determining their orbital orientations and parameters, revealing mostly coplanar orbits with some high inclination cases, and assessing their dynamical stability.

## Contribution

It provides new precise orbital measurements and relative orientations for several nearby multiple star systems, expanding the limited data on their configurations.

## Key findings

- Most systems have moderate outer to inner period ratios.
- Outer orbits are generally moderately eccentric.
- Most systems are dynamically stable, with some high inclination cases.

## Abstract

This work extends the still modest number of multiple stars with known relative orbit orientation. Accurate astrometry and radial velocities are used jointly to compute or update outer and inner orbits in three nearby triple systems HIP 101955 (orbital periods 38.68 and 2.51 years), HIP 103987 (19.20 and 1.035 years), HIP 111805 (30.13 and 1.50 years) and in one quadruple system HIP 2643 (periods 70.3, 4.85 and 0.276 years), all composed of solar-type stars. The masses are estimated from the absolute magnitudes and checked using the orbits. The ratios of outer to inner periods (from 14 to 20) and the eccentricities of the outer orbits are moderate. These systems are dynamically stable, but not very far from the stability limit. In three systems all orbits are approximately coplanar and have small eccentricity, while in HIP 101955 the inner orbit with e=0.6 is highly inclined.