Physical Properties and Evolutionary States of EA-type Eclipsing Binaries Observed by LAMOST

TL;DR

This study analyzes the physical properties and evolutionary stages of over 3000 EA-type eclipsing binaries observed by LAMOST, revealing their metallicity distributions, period limits, and evolutionary pathways into W UMa-type binaries.

Contribution

The paper provides a comprehensive catalog of EA-type binaries with derived spectral and physical parameters, and investigates their evolutionary processes and metallicity characteristics.

Findings

EAs have a period limit of about 6 days for tidal locking.

EAs are generally younger and have higher metallicity than EWs.

EWs may form from EAs through angular momentum loss and mass transfer, with some influenced by third bodies or compact objects.

Abstract

About 3196 EA-type binaries (EAs) were observed by LAMOST by June 16, 2017 and their spectral types were derived. Meanwhile stellar atmospheric parameters of 2020 EAs were determined. In the paper, those EAs are catalogued and their physical properties and evolutionary states are investigated. The period distribution of EAs suggests that the period limit of tidal locking for the close binaries is about 6 days. It is found that the metallicity of EAs is higher than that of EWs indicating that EAs are generally younger than EWs and they are the progenitors of EWs. The metallicities of long-period EWs (0.4 < P < 1 days) are the same as those of EAs with the same periods, while their values of Log (g) are usually smaller than those of EAs. These support the evolutionary process that EAs evolve into long-period EWs through the combination of angular momentum loss (AML) via magnetic braking and case A mass transfer. For short-period EWs, their metallicities are lower than those of EAs, while their gravitational accelerations are higher. These reveal that they may be formed from cool short-period EAs through AML via magnetic braking with little mass transfer. For some EWs with high metallicities, they may be contaminated by material from the evolution of unseen neutron stars and black holes or they have third bodies that may help them to form rapidly through a short timescale of pre-contact evolution. The present investigation suggests that the modern EW populations may be formed through the combination of aforementioned mechanisms.