Extremely low mass ratio contact binaries -- I. the first photometric and spectroscopic investigations of ten systems

TL;DR

This study presents the first combined photometric and spectroscopic analysis of ten extremely low mass ratio contact binaries, revealing their evolutionary states, activity, and stability, and providing new insights into their late-stage evolution.

Contribution

It is the first comprehensive investigation of ten contact binaries with mass ratios below 0.15, including their physical properties, activity, period changes, and evolutionary status.

Findings

All ten systems have mass ratios below 0.15.

Most are deep contact binaries with long-term period changes.

Spectroscopic analysis shows chromospheric activity in all targets.

Abstract

The photometric and spectroscopic investigations of ten contact binaries were presented for the first time. It is discovered that the mass ratios of all the ten targets are smaller than 0.15, they are extremely low mass ratio contact binaries. Seven of them are deep contact binaries, two are medium contact binaries, while only one is a shallow contact system. Five of them show O'Connell effect, and a dark spot on one of the two components can lead to a good fit of the asymmetric light curves. The orbital period studies of the ten binaries reveal that they all exhibit long-term period changes, six of them are increasing, while the others are shrinking. The LAMOST spectra were analyzed by the spectral subtraction method, and all the ten targets exhibit excess emissions in the H$_\alpha$ line, indicating chromospheric activity. The evolutionary states of the two components of the ten binaries were studied, and it is found that their evolutionary states are identical to those of the other contact binaries. Based on the study of the relation between orbital angular momentum and total mass, we discovered the ten systems may be at the late evolutionary stage of a contact binary. The initial masses of the two components and the ages of them were obtained. By calculating the instability parameters, we found that the ten contact binaries are relatively stable at present.