The unusual quadruple system HD 91962 with a "planetary" architecture

TL;DR

This study characterizes the complex quadruple star system HD 91962, revealing nearly coplanar orbits, resonances, and estimated component masses, suggesting a formation from core collapse and disk migration.

Contribution

It provides detailed orbital parameters and mass estimates for all components, and discusses the system's likely formation process, which is a novel insight into such multiple star systems.

Findings

Orbits are nearly coplanar with small eccentricities.

The middle and inner orbits are likely in a 1:19 resonance.

Component masses are estimated with high precision.

Abstract

The young nearby solar-type star HD 91962 is a rare quadruple system where three companions revolve around the main component with periods of 170.3 days, 8.85 years, and 205 years. The two outer orbits are nearly co-planar, and all orbits have small eccentricities. We refine the visual orbit of the outer pair, determine the combined spectro-interferometric orbit of the middle 8.8-yr pair and the spectroscopic orbit of the inner binary. The middle and inner orbits are likely locked in a 1:19 resonance, the ratio of the outer and middle periods is ~23. The masses of all components are estimated (inside-out: 1.14, 0.32, 0.64, 0.64 solar mass), the dynamical parallax is 27.4+-0.6 mas. We speculate that this multiple system originated from collapse of an isolated core and that the companions migrated in a dissipative disk. Other multiple systems with similar features (coplanarity, small eccentricity, and period ratio around 20) are known.