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arXiv 2601.12972astro-ph.EP
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探索小行星家族的旋转特性及YORP效应

Exploring rotational properties and the YORP effect in asteroid families

University of Padova(帕多瓦大学);University of Tokyo(东京大学);Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange(蔚蓝海岸大学,蔚蓝海岸天文台,法国国家科学研究中心,拉格朗日实验室)

Gabriele Bertinelli, Wen-Han Zhou, Paolo Tanga

AI总结:

该研究通过分析小行星家族的旋转特性,揭示了YORP效应及碰撞对自转演化的影响,为小行星家族年龄估算提供了新方法。

摘要:

小行星家族的长期动力学演化由轨道和旋转演化之间的相互作用所驱动,这些相互作用由热力和碰撞引起。我们旨在通过观测追溯主带小行星家族在Gyr时间尺度上的旋转演化。我们分析了8739颗具有自转周期测量值和3794颗具有倾角确定值的小行星,覆盖28个年龄从14~Myrs到3Gyrs的小行星家族。我们引入了一个无量纲时间尺度,将每个小行星的家族年龄归一化为其经典YORP时间尺度,从而能够直接比较不同演化阶段的旋转状态。我们检查了两个关键可观测变量:慢自转比例(周期大于或等于30小时)和偏振分数(小行星自转轴与家族V形分布中位置的一致程度,根据Yarkovsky理论)。两个量的演化被拟合以确定特征转变时间尺度。我们发现慢自转比例随着t急剧增加,并在t≈20处达到饱和,慢自转比例约为0.25。这表明随机YORP时间尺度τ_YORP,stoc≈10τ_YORP,与包含翻滚和减弱YORP扭矩的旋转演化模型相比。偏振分数在t≈16时达到最大值≈0.8,然后向随机极限f_pol→0.5衰减,对于t≈20时,表明碰撞性自转重定向的主导作用随时间增加。不同小行星家族中的旋转特性提供了旋转演化的关键线索,并可作为新的维度用于估算小行星家族年龄,特别是在LSST时代的更多数据情况下。

英文摘要:

The long-term dynamical evolution of asteroid families is governed by the interplay between orbital and rotational evolution driven by thermal forces and collision. We aim to observationally trace the rotational evolution of main-belt asteroid families over Gyr timescales. We analyzed rotational properties of 8739 asteroids with spin period measurements and 3794 asteroids with obliquity determinations across 28 asteroid families spanning ages from 14~Myrs to 3~Gyrs. We introduced a dimensionless timescale that normalizes each asteroid's family age by its classical YORP timescale, enabling direct comparison of rotational states across different evolutionary stages. We examined two key observables: the fraction of slow rotators (periods greater than or equal to 30 hours) and the polarization fraction (the degree to which asteroid spin poles align correctly with their position in the family's V-shape distribution according to the Yarkovsky theory). Evolution of both quantities were fitted to identify characteristic transition timescales. We discovered that the slow-rotator fraction increases steeply with $t$ and saturates at $f_{\rm slow} \simeq 0.25$ around a breakpoint $t_{\rm bp} \simeq 20$. This implies a stochastic YORP timescale $τ_{\rm YORP,stoc} \simeq 10\,τ_{\rm YORP}$ by comparison with rotational evolution models that include tumbling and weakened YORP torques. The polarization fraction reaches a maximum of $\simeq 0.8$ at $t \simeq 16$ and then decays toward the random limit $f_{\rm pol} \rightarrow 0.5$ for $t \gtrsim 20$, indicating an increasing dominance of collisional spin reorientation over time. The rotation properties within different asteroid families offer crucial clues to rotation evolution and can serve as a new dimension for age estimation of asteroid families with more data in the LSST era.

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