Three-dimensional Orbit and Dynamical Masses of GJ 105 AC

TL;DR

This paper presents a precise orbital and mass analysis of the GJ 105 AC binary system, establishing it as a key benchmark for stellar models due to its well-measured, effectively single star properties.

Contribution

The study provides the first full orbital analysis of GJ 105 AC, yielding highly accurate dynamical masses and demonstrating its suitability as a benchmark star for stellar evolution models.

Findings

Dynamical masses of GJ 105 A and C are 0.78 and 0.098 solar masses.

The orbital period is approximately 76 years, with full periapsis coverage achieved.

GJ 105 AC has one of the widest separations among stars with precise mass measurements.

Abstract

The precision of stellar models is higher than the precision at which we are able to measure the masses of most stars, with the notable exception of binaries where we can determine dynamical masses of the component stars. In addition to well-measured stellar properties, the ideal benchmark star is far enough from its companion that its properties are indistinguishable from an otherwise identical single star. Currently, there are a handful of stars with precise ($\pm$3 %), model-independent mass measurements that are "effectively single" and for which we can obtain clean spectra (i.e. spectra that are not blended with a close companion). In this paper, we introduce GJ 105 AC as the newest members of this exclusive population. We present an updated orbital analysis for the long-period K3+M7 binary GJ 105 AC. We jointly analyze radial velocity (RV) and relative astrometry data, including new RVs from the Miniature Exoplanet Radial Velocity Array (MINERVA) that capture the full periapsis passage and the RV minimum of the $76.0 \pm 1.3$ yr orbit for the first time. We derive precise dynamical masses of $M_1 = 0.78 \pm 0.02\, \mathrm{M}_\odot$ and $M_2 = 0.098 \pm 0.002\, \mathrm{M}_\odot$. We find that of all stars with similarly precise masses (~2%), GJ 105 AC stands out as having the widest on-sky separation after $\alpha$ Centauri AB, making it one of the most easily accessible to spectroscopy, as well as the the second-widest true separation, ensuring that its members are truly "effectively single" in terms of their evolution.