具有大间隔的双星小行星的自转周期--用观测结果对抗逃逸的喷出物双星模型
Rotation Periods of Binary Asteroids with Large Separations - Confronting the Escaping Ejecta Binaries Model with Observations
摘要：
Durda等人（2004年）利用数值模型提出，具有大间隔的双星小行星，称为逃逸抛射双星，可能是由破坏性撞击事件抛射出的碎片产生的。最近发现的六颗双星小行星被认为是EEB，因为它们的成分之间的分离度很高（~100 > a/Rp > ~20）。然而，由我们的小组和其他人测量的六个物体中的四个的旋转周期表明，这些疑似EEB的旋转速率为2.5至4小时。由于这些二元小行星的组成部分尺寸很小，与这种快速旋转有关，我们得出结论，旋转裂变机制，这是热YORP效应的结果，是最有可能的形成场景。此外，对这些天体的YORP效应进行缩放显示，其时间尺度短于承载这些二元小行星的三个相关平山家族的估计年龄。因此，只有最大的（D~19公里）疑似小行星，（317）Roxane，实际上可能是唯一已知的EEB。此外，我们的研究结果证实了（3749）Balam的三重性质，通过测量其光变曲线上的相互事件，这些事件与附近卫星的轨道周期相匹配。对（1509）Esclangona在不同显灵时的测量显示了一种独特的光变曲线形状，这可以用颜色变化来解释。
英文摘要：
Durda et al. (2004), using numerical models, suggested that binary asteroids with large separation, called Escaping Ejecta Binaries (EEBs), can be created by fragments ejected from a disruptive impact event. It is thought that six binary asteroids recently discovered might be EEBs because of the high separation between their components (~100 > a/Rp > ~20). However, the rotation periods of four out of the six objects measured by our group and others and presented here show that these suspected EEBs have fast rotation rates of 2.5 to 4 hours. Because of the small size of the components of these binary asteroids, linked with this fast spinning, we conclude that the rotational-fission mechanism, which is a result of the thermal YORP effect, is the most likely formation scenario. Moreover, scaling the YORP effect for these objects shows that its timescale is shorter than the estimated ages of the three relevant Hirayama families hosting these binary asteroids. Therefore, only the largest (D~19 km) suspected asteroid, (317) Roxane, could be, in fact, the only known EEB. In addition, our results confirm the triple nature of (3749) Balam by measuring mutual events on its lightcurve that match the orbital period of a nearby satellite in addition to its distant companion. Measurements of (1509) Esclangona at different apparitions show a unique shape of the lightcurve that might be explained by color variations.
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