# Physical Properties and Catalogue of EW-type Eclipsing Binaries Observed by LAMOST

## TL;DR

This paper catalogs and analyzes the physical properties of EW-type eclipsing binaries observed by LAMOST, revealing their age, metallicity distribution, and evolutionary characteristics based on spectroscopic data.

## Contribution

The study provides a comprehensive catalog of EW binaries with spectroscopic parameters and analyzes their properties and evolutionary implications, highlighting the role of magnetic braking and third bodies.

## Key findings

- 80.6% of stars have metallicity below zero, indicating they are old stellar populations.
- Short-period EWs tend to be older with lower metallicities.
- Correlations between orbital period and stellar parameters are influenced by third bodies and measurement errors.

## Abstract

Numerous EWs were discovered by several deep photometric survey and there are about 40785 EW-type binary systems listed in the international variable star index (VSX) by March 13, 2017. 7938 of them were observed by LAMOST by November 30, 2016 and their spectral types were given. Stellar atmospheric parameters of 5363 EW-type binary stars were determined based on good spectroscopic observations. In the paper, those EWs were catalogued and their properties are analyzed. The distributions of the orbital period (P), the effect temperature (T), the gravitational acceleration (Log(g)), the metallicity ([Fe/H]) and the radial velocity (RV) are presented for those observed EW-type systems. It is shown that about 80.6\% sample stars have metallicity below zero indicating that EW-type systems are old stellar population. This is in agreement with the the conclusion that the EW binaries are formed from moderately close binaries through angular momentum loss via magnetic braking that takes a few hundred million to a few billion years. The unusual high metallicities of a few percent of EWs may be caused by contaminating of material from the evolution of unseen neutron stars and black holes in the systems. The correlations between the orbital period and the effect temperature, the gravitational acceleration and the metallicity are presented and their scatters are mainly caused by (i) the presence of the third bodies and (ii) the wrong determined periods sometimes. It is shown that some EW contain evolved component stars and the physical properties of EWs are mainly depending on their orbital periods. It is found that the extremely short-period EWs may be older than their long-period cousins because they have lower metallicities. This reveals that they have a longer timescale of pre-contact evolution and their formation and evolution are mainly driven by angular momentum loss via magnetic braking.