Unveiling the Origins and Dynamics of the Hierarchical Triple Star System CN Lyn

TL;DR

This paper provides a comprehensive analysis of the hierarchical triple star system CN Lyn, revealing detailed stellar parameters, chemical compositions, and orbital dynamics, and suggesting the third star was captured from the Galactic halo.

Contribution

The study offers the first detailed characterization of CN Lyn's components, combining spectroscopic, photometric, and kinematic data to understand its origin and stability.

Findings

Eclipsing components have masses around 1.15 M_sun and are about 3.9 Gyr old.

Third component is metal-poor, older, and likely captured from the Galactic halo.

System is dynamically stable as a hierarchical triple.

Abstract

In this study we present a detailed analysis of CN Lyn, an overlooked triple star system, by combining spectroscopic data from the literature, photometric \textit{TESS} data, and kinematic techniques. We updated the fundamental parameters of the known eclipsing components in the system with high precision. The chemical composition of both eclipsing components (Aab) and the third component (B) in the system were calculated with great accuracy. According to our analysis the mass, radius, and metallicity of the eclipsing components are $1.166_{-0.012}^{+0.013}\,M_\odot$, $1.786_{-0.014}^{+0.013}\,R_\odot$, and $-0.78_{-0.02}^{+0.02}$ dex for Aa and $1.143_{-0.012}^{+0.013}\,M_\odot$, $1.651_{-0.013}^{+0.014}\,R_\odot$, and $-0.55_{-0.02}^{+0.03}$ dex for Ab. The pair's age is $3.89_{-0.10}^{+0.10}$ Gyr. The mass, radius, metallicity, and age for B are $0.85_{-0.23}^{+0.23}\,M_\odot$, $1.436_{-0.023}^{+0.026}\,R_\odot$, $-1.83_{-0.11}^{+0.09}$ dex, and $12.5_{-2.5}^{+2.5}$ Gyr, respectively. It is also found that the triple system (AabB) satisfies the stability criteria for the hierarchical triple system. Kinematic and Galactic orbital parameters of CN Lyn were obtained from the astrometric and spectroscopic data of the system. Dynamical orbital analyses, taking into account the ages of the component stars in the central binary system (A) show that the CN Lyn originated at the metal-poor edge of the Galactic disk. The third component of the system was found to be a member of the halo population in terms of age, $\alpha$ elements and metal abundance. Given the different chemical abundances and age of B compared to A, this suggests that the third component was captured by the central system in a region with weak gravitational interactions far beyond the Galactic disc.