A novel approach to determining the age of stellar clusters: application to NGC 188

TL;DR

This paper introduces a new method for determining the age of stellar clusters by jointly fitting binary star data and spectral energy distributions, applied to NGC 188, resulting in an age estimate of approximately 6.4 billion years.

Contribution

It presents a novel joint fitting approach combining RVs and SEDs for binary stars to estimate cluster age, incorporating multiple stellar models for uncertainty analysis.

Findings

Estimated age of NGC 188 is 6.41 Gyr.

Distance to NGC 188 is approximately 1850 pc.

Method provides an independent age determination using binary star data.

Abstract

We present a new independent determination for the age of one of the oldest open clusters, NGC 188: $6.41 \pm 0.33$ Gyr. We utilize a novel approach where we jointly fit the radial velocities (RVs) and spectral energy distributions (SED) of six binary star systems in the cluster. The joint fit has 21 free parameters: 12 stellar masses, 6 orbital inclination angles, as well as a common cluster age, distance, and extinction, $A_V$. The fit to the SEDs utilizes MIST stellar isochrones, and the fitted stellar parameters are presented in HR diagrams (R - $T_{\rm eff}$, R - M, and M - $T_{\rm eff}$) showing the stars' different states of evolution. These isochrones are compared with PARSEC and Y2 isochrones to obtain an estimate of the uncertainties introduced by different stellar models. Of the 3017 stars taken from the NGC 188 field, 333 possible member stars were selected using Gaia data and analyzed separately for their mean distances and proper motions. We find a distance to NGC 188 of $1850 \pm 12$ pc compared with the independent photometric distance found from the SED fitting of $1897 \pm 58$ pc.