MESA Models of the Evolutionary State of the Interacting Binary epsilon Aurigae

TL;DR

This study uses MESA simulations to model the evolutionary history of epsilon Aurigae, matching key observational features and providing insights into its current state as a post-RGB/pre-AGB binary system.

Contribution

First detailed MESA-based evolutionary model of epsilon Aurigae that aligns with multiple observational constraints and offers a foundation for future research.

Findings

Model reproduces observed period of 27.1 years

Achieves a 12 C/ 13 C ratio of 5

Suggests the donor is a post-RGB/pre-AGB star

Abstract

Using MESA code (Modules for Experiments in Stellar Astrophysics, version 9575), an evaluation was made of the evolutionary state of the epsilon Aurigae binary system (HD 31964, F0Iap + disk). We sought to satisfy several observational constraints: 1) requiring evolutionary tracks to pass close to the current temperature and luminosity of the primary star; 2) obtaining a period near the observed value of 27.1 years; 3) matching a mass function of 3.0; 4) concurrent Roche lobe overflow and mass transfer; 5) an isotopic ratio 12 C/ 13 C = 5 and, (6) matching the interferometrically determined angular diameter. A MESA model starting with binary masses of 9.85 + 4.5 Msun , with a 100 day initial period, produces a 1.2 + 10.6 Msun result having a 547 day period, and a single digit 12 C/ 13 C ratio. These values were reached near an age of 20 Myr, when the donor star comes close to the observed luminosity and temperature for epsilon Aurigae A, as a post-RGB/pre-AGB star. Contemporaneously, the accretor then appears as an upper main sequence, early B-type star. This benchmark model can provide a basis for further exploration of this interacting binary, and other long period binary stars.