The reason for the occurrence of W-type contact binaries
Abstract
For more than half a century, the puzzling W-type phenomenon in contact binaries has challenged astrophysicists. In these systems, the less massive component exhibits a higher surface temperature than its more massive companion, which is a reversal of the typical A-type configuration, where the more massive star is hotter. This counterintuitive temperature inversion defies the basic stellar physics and still lacks a widely accepted explanation. In this study, we assembled a sample of over 3,000 extensively observed contact binaries and derived their complete set of physical parameters. Our statistical analysis revealed a strong positive correlation between the occurrence of W-type contact binaries and the intensity and frequency of magnetic activities. This result strongly supports the hypothesis that magnetic activities are the primary driver of the W-type phenomenon and offers a compelling explanation for the observed transitions between the W-type and A-type.
Keywords
Cite
@article{arxiv.2601.15672,
title = {The reason for the occurrence of W-type contact binaries},
author = {Jia Zhang and Sheng-Bang Qian and Li-Ying Zhu and Xu-Zhi Li},
journal= {arXiv preprint arXiv:2601.15672},
year = {2026}
}