Post Main Sequence Orbital Circularization of Binary Stars in the Large and Small Magellanic Clouds

TL;DR

This study analyzes the orbital eccentricities of eclipsing binary stars in the Magellanic Clouds, revealing rapid circularization in systems with evolved stars beyond the main sequence.

Contribution

It provides a large-scale statistical analysis of binary star orbits in the Magellanic Clouds, highlighting the impact of stellar evolution on orbital circularization.

Findings

Close binary stars tend to have circular orbits.

Eccentricity decreases as stars evolve beyond the main sequence.

Orbital circularization is rapid in systems with evolved stars.

Abstract

We present results from a study of the orbits of eclipsing binary stars (EBs) in the Magellanic Clouds. The samples comprise 4510 EBs found in the Large Magellanic Cloud (LMC) by the MACHO project, 2474 LMC EBs found by the OGLE-II project (of which 1182 are also in the MACHO sample), 1380 in the Small Magellanic Cloud (SMC) found by the MACHO project, and 1317 SMC EBs found by the OGLE-II project (of which 677 are also in the MACHO sample); we also consider the EROS sample of 79 EBs in the bar of the LMC. Statistics of the phase differences between primary and secondary minima allow us to infer the statistics of orbital eccentricities within these samples. We confirm the well-known absence of eccentric orbit in close binary stars. We also find evidence for rapid circularization in longer period systems when one member evolves beyond the main sequence, as also found by previous studies.