On the origin and evolutionary state of RZ Cas, KO Aql and S Equ

TL;DR

This paper investigates the evolutionary stages of RZ Cas, KO Aql, and S Equ by comparing observed properties with models of binary evolution, revealing their early main sequence status and initial mass ratio constraints.

Contribution

It provides new insights into the initial mass ratios and evolutionary states of these binary systems through detailed comparison with evolutionary models.

Findings

Gainters are in early main sequence stage with Xc > 0.5

KO Aql is nearly unevolved, close to thermal equilibrium

Initial donor/gainer mass ratios must exceed three

Abstract

Aims. Determination of the present evolutionary state and the restrictions on the initial mass ratios of RZ Cas, KO Aql and S Equ. Methods. Comparison of mass gaining stars with evolutionary models of single stars with the same mass and subsequent comparison with accretion tracks from simultaneous conservative binary evolution. Results. The gainers are in an early main sequence stage (Xc greater than 0.5), with KO Aql being almost unevolved (assuming quasi-thermal equilibrium). The initial donor/gainer mass ratios Mdi/Mgi must be larger than three to obtain the present mass and luminosity of the gainers.