CARE AND FEEDING OF FROGS
CARE AND FEEDING OF FROGS
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青蛙的护理和喂养
DOI：
10.1088/0004-6256/143/1/9
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
E. Chiang
中科院分区：
文献类型：
--
作者：
M. Pan;E. Chiang
“螺旋桨”是土星A环的特征，与打开部分间隙的小卫星有关。它们表现出非开普勒运动（Tiscareno等人）;观测最好的螺旋桨“Blériot”的经度残差似乎与周期为104年的正弦曲线一致。潘和蒋提出，螺旋桨小卫星在与共轨环材料的“青蛙共振”中自由振动。通过与限制性三体问题类比，他们将共轨材料视为旋转坐标系中的静止物质，而忽略了非共轨材料。在这里，我们使用简单的数值实验来扩展青蛙模型，包括反馈由于差距的运动，和阻力与Lindblad磁盘扭矩，导致I型迁移。因为小卫星产生了差距，我们期望差距质心跟踪小卫星，但只有在一个时间延迟tdelay之后，这个时间延迟是环粒子从与小卫星会合到差距末端的时间。我们发现，青蛙的振动可以持续只有当tdelay超过青蛙的振动周期Plib，如果从Lindblad扭矩阻尼平衡驱动从共轨扭矩。如果tdelay大于Pllib，则振动振幅衰减为零。在Blériot的情况下，青蛙共振模型可以重现观测到的天平动周期Plib 4 yr。然而，我们简单的反馈处方表明，布雷里奥的tdelay = 0.01Plib，这与观测到的260 km的天平动振幅不一致。我们敦促更准确地处理反馈，以测试我们的玩具模型的假设。
“Propellers” are features in Saturn's A ring associated with moonlets that open partial gaps. They exhibit non-Keplerian motion (Tiscareno et al.); the longitude residuals of the best-observed propeller, “Blériot,” appear consistent with a sinusoid of period ∼4 years. Pan & Chiang proposed that propeller moonlets librate in “frog resonances” with co-orbiting ring material. By analogy with the restricted three-body problem, they treated the co-orbital material as stationary in the rotating frame and neglected non-co-orbital material. Here we use simple numerical experiments to extend the frog model, including feedback due to the gap's motion, and drag associated with the Lindblad disk torques that cause Type I migration. Because the moonlet creates the gap, we expect the gap centroid to track the moonlet, but only after a time delay tdelay, the time for a ring particle to travel from conjunction with the moonlet to the end of the gap. We find that frog librations can persist only if tdelay exceeds the frog libration period Plib, and if damping from Lindblad torques balances driving from co-orbital torques. If tdelay ≪ Plib, then the libration amplitude damps to zero. In the case of Blériot, the frog resonance model can reproduce the observed libration period Plib ≃ 4 yr. However, our simple feedback prescription suggests that Blériot's tdelay ∼ 0.01Plib, which is inconsistent with the observed libration amplitude of 260 km. We urge more accurate treatments of feedback to test the assumptions of our toy models.
土星环中小卫星引起的结构：对卡西尼号任务的影响
影响因子：
5.2
作者：
Sremčevič
通讯作者：
Sremčevič
固体粒子环中小卫星的迁移：理论及其在土星螺旋桨中的应用
DOI：
10.1088/0004-6256/140/4/944
发表时间：
2010
期刊：
The Astronomical Journal
影响因子：
--
作者：
Crida A
通讯作者：
Crida A