Two Ultralow-mass-ratio Binary Systems at Critical Evolutionary Stages

作者：Di-Fu Guo, Kai Li, Fen Liu, Li-Heng Wang, Huai-Zhen Li, Xu Chen, Xiang Gao · 发表于：The Astronomical Journal · 年份：2025 · DOI：10.3847/1538-3881/ade9c0 · 被引用次数：7 · 研究领域：Stellar, planetary, and galactic studies、Astrophysics and Star Formation Studies、Astro and Planetary Science

Abstract In this paper, we present photometric observations and period analysis of two totally eclipsing binaries with extremely low-amplitude light curves. Both binaries exhibit typical W Ursae Majoris-type light curves with total eclipses, allowing for the precise determination of the mass ratios. Light-curve solutions were derived using the Python package PHysics Of Eclipsing BinariEs in combination with a Markov Chain Monte Carlo framework. Both WISE J053525.4–200442 (hereafter J053525) and ASASSN-V J175200.35+361805.2 (hereafter J175200) are identified as shallow contact binaries with ultralow mass ratios. Specifically, J053525 exhibits a mass ratio of q ≈ 0.124 and a marginal contact degree of f ∼ 22%, while J175200 has q ≈ 0.027 and a contact degree of f ∼ 13%. Notably, J175200 represents the most extreme mass ratio observed in contact binaries to date. However, due to degeneracies between mass ratio and third-light contributions in purely photometric analyses, the derived mass ratios should be interpreted as lower limits, especially for J175200. The evolutionary states of these systems differ significantly. For J053525, a long-term period decrease is detected, with the orbital period derivative calculated as d P d t = − 1.99 × 1 0 − 6 day yr − 1 . In contrast, J175200 shows a period increase: d P d t = 1.93 × 1 0 − 7 day yr − 1...