Models for Sixty Double-Lined Binaries containing Giants

TL;DR

This study compares observed data of 60 binary star systems with theoretical models including mass loss, core overshooting, and tidal friction, revealing reasonable fits in most cases but also notable discrepancies and complex evolutionary histories.

Contribution

It provides an extensive comparison of observed binary star parameters with models incorporating multiple physical processes, highlighting successes and limitations of current theories.

Findings

42 systems fit models reasonably well

11 systems show more or less mass loss than predicted

4 systems have orbital eccentricities not matching models

Abstract

The observed masses, radii and temperatures of 60 medium- to long-period binaries, most of which contain a cool, evolved star and a hotter less-evolved one, are compared with theoretical models which include (a) core convective overshooting, (b)mass loss, possibly driven by dynamo action as in RS CVn binaries, and (c) tidal friction, including its effect on orbital period through magnetic braking. A reasonable fit is found in about 42 cases, but in 11 other cases the primaries appear to have lost either more mass or less mass than the models predict, and in 4 others the orbit is predicted to be either more or less circular than observed. Of the remaining 3 systems, two ($\gamma$ Per and HR 8242) have a markedly `over-evolved' secondary, our explanation being that the primary component is the merged remnant of a former short-period sub-binary in a former triple system. The last system (V695 Cyg) defies any agreement at present. Mention is also made of three other systems (V643 Ori, OW Gem and V453 Cep), which are relevant to our discussion.