The Excited Spin State of 1I/2017 U1 ‘Oumuamua
The Excited Spin State of 1I/2017 U1 ‘Oumuamua
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1I/2017 U1 ‘Oumuamua 的兴奋旋转状态
DOI：
10.3847/2041-8213/aab370
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
J. Keane
中科院分区：
文献类型：
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作者：
M. Belton;O. Hainaut;K. Meech;B. E. Mueller;J. Kleyna;H. Weaver;M. Buie;M. Drahus;Piotr Guzik;R. Wainscoat;W. Waniak;B. Handzlik;S. Kurowski;Siyi Xu;S. Sheppard;M. Micheli;H. Ebeling;J. Keane
我们发现，Oumuamua的激发自旋可能处于高能长轴模式（LAM）状态，这意味着它的形状可能与以前研究中发现的高度拉长的形状相去甚远。CLEAN和ANOVA算法被用来分析Oumuamua的光曲线，使用818个观测超过29.3天。发现两个基本周期的频率分别为（2.77 ± 0.11）和（6.42 ± 0.18）周/日，分别对应于（8.67 ± 0.34）hr和（3.74 ± 0.11）hr。相位数据表明，光变曲线不是以简单的方式重复，而是近似地在2.77周/天时显示出双最小值，在6.42周/天时显示出单最小值。Oumuamua可能在LAM或短轴模式（SAM）下旋转。对于这两个天体，长轴绕总角动量矢量进动的平均周期为（8.67 ± 0.34）hr，而对于我们发现的三个LAM，长轴绕总角动量矢量进动的可能周期分别为6.58，13.15和54.48 hr，其中54.48 hr的可能性最大。Oumuamua也可能以这些值的一半的相应周期章动。我们还发现了两种可能的SAM状态，其中'Oumuamua绕长轴振荡，可能的周期为13.15和54.48小时。在这种情况下，任何章动发生相同的周期。自旋状态的确定，章动的幅度，总角动量矢量（TAMV）的方向，和平均总自旋周期可能与一个直接的模型拟合的光变曲线。我们发现，'Oumuamua是“雪茄形”，如果接近其最低的旋转能量，和一个非常扁球体，如果接近其最高能量状态。
We show that ‘Oumuamua’s excited spin could be in a high-energy long axis mode (LAM) state, which implies that its shape could be far from the highly elongated shape found in previous studies. CLEAN and ANOVA algorithms are used to analyze ‘Oumuamua’s lightcurve using 818 observations over 29.3 days. Two fundamental periodicities are found at frequencies (2.77 ± 0.11) and (6.42 ± 0.18) cycles/day, corresponding to (8.67 ± 0.34) hr and (3.74 ± 0.11) hr, respectively. The phased data show that the lightcurve does not repeat in a simple manner, but approximately shows a double minimum at 2.77 cycles/day and a single minimum at 6.42 cycles/day. ‘Oumuamua could be spinning in either the LAM or short axis mode (SAM). For both, the long axis precesses around the total angular momentum vector with an average period of (8.67 ± 0.34) hr. For the three LAMs we have found, the possible rotation periods around the long axis are 6.58, 13.15, or 54.48 hr, with 54.48 hr being the most likely. ‘Oumuamua may also be nutating with respective periods of half of these values. We have also found two possible SAM states where ‘Oumuamua oscillates around the long axis with possible periods at 13.15 and 54.48 hr. In this case any nutation occurs with the same periods. Determination of the spin state, the amplitude of the nutation, the direction of the total angular momentum vector (TAMV), and the average total spin period may be possible with a direct model fit to the lightcurve. We find that ‘Oumuamua is “cigar-shaped,” if close to its lowest rotational energy, and an extremely oblate spheroid if close to its highest energy state.