Two twin binaries with nearly identical components: KIC 4826439 and KIC 6045264

TL;DR

This paper reports the discovery and analysis of two nearly identical twin binary star systems using Kepler data, introduces a new method for determining their parameters without radial velocities, and discusses their evolutionary paths.

Contribution

The study presents a novel method to derive absolute parameters of twin binaries solely from light curves, spectra, and isochrones, without requiring radial velocity measurements.

Findings

Very low proportion of twin binaries found, challenging previous excess hypotheses.

Both systems have components with less than 2% parameter differences.

Evolutionary analysis suggests different future outcomes for the two systems.

Abstract

Two twin binaries, KIC 4826439 and KIC 6045264, with very similar component stars were found photometrically based on $\textit{Kepler}$ eclipsing binary light curves. The absolute parameters of the massive components are 1.156(0.03)$M_\odot$, 1.881(0.02)$R_\odot$, 6065K for KIC 4826439, and 0.874(0.3)$M_\odot$, 1.206(0.02)$R_\odot$, 6169(30)K for KIC 6045264. The differences between the components are less than two percents for all the parameters. A very low proportion of the twin binaries ($2/1592\approx0.13\%$) was found, which does not support the previous findings of the excesses of twins on binary mass ratio distribution, but support a deficiently low proportion of twins. A new method is practiced to work out the absolute parameters of the two twins without the radial velocities. This method requires the solution of the light curves, the spectra and the evolutionary isochrones of covering the complete stellar parameter space, simultaneously. We also studied their evolution tracks that: KIC 4826439 will experience an unstable mass transfer stage followed by an unclear ending, and KIC 6045264 will become a single star via an over-contact phase. It seems highly unlikely that the two twin binaries will produce twin degenerate binaries, although they have quite similar components.