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arXiv · 2601.15672

The reason for the occurrence of W-type contact binaries

Jia Zhang·Sheng-Bang Qian·Li-Ying Zhu·Xu-Zhi Li
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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.

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Jia Zhang, Sheng-Bang Qian, Li-Ying Zhu, Xu-Zhi Li. 2026-01-22. The reason for the occurrence of W-type contact binaries. https://doi.org/10.3847/1538-4365%2Fae21ce

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