Modelling early-type stars in eclipsing binaries of open clusters: a new method for age determination from ratio of radii

TL;DR

This paper introduces a new method for estimating the ages of binary star systems in open clusters by using the ratio of stellar radii and masses, providing a more precise and composition-independent approach.

Contribution

The paper develops a novel, simple formula for relative age determination of eclipsing binaries based on radius and mass ratios, improving accuracy and independence from chemical composition assumptions.

Findings

The age estimates differ by up to 40% from traditional isochrone fitting.

The new method is nearly independent of chemical composition assumptions.

It provides a more precise and observationally robust age determination.

Abstract

Binary systems, in particular eclipsing binaries, are essential sources of our knowledge of the fundamental properties of stars. The ages of binaries, members of open clusters, are constrained by their own fundamental properties and by those of the hosting cluster. The ages of eleven open clusters are here found by constructing models for the components of twelve eclipsing binaries. The difference between the ages we found and the ages of the clusters derived from isochrone fitting is up to 40%. For the binary system V497 Cep in NGC 7160, the difference is about 100%. Binary systems whose primary component is aboutto complete main-sequence life time, such as V453 Cyg and V906 Sco, are the most suitable systems for age determination. Using model results for these stars, we derive an expression for sensitive and uncomplicated relative age determination of binary systems (age divided by the main-sequence life time of the primary star). The expression is given as logarithm of radii ratio divided by a logarithm of mass ratio. Two advantages of this expression are that (i) it is nearly independent of assumed chemical composition of the models because of the appearance of the ratio of radii, and (ii) the ratios of radii and masses are observationally much more precise than their absolute values. We also derive another expression using luminosities rather than radii and compare results.