其他世界的天气五、三颗自转最快的超冷矮星
Weather on Other Worlds. V. The Three Most Rapidly Rotating Ultra-Cool Dwarfs
摘要：
我们提出的快速光度变化的发现，在三个超冷矮星从长时间的监测与斯皮策太空望远镜。T7、L3.5和L 8矮星的光度周期是迄今为止已知的最短的：分别为${1.080}^{+0.004}_{-0.005}$ h、${1.14}^{+0.03}_{-0.01}$ h和${1.23}^{+0.01}_{-0.01}$ h。我们确认通过中等分辨率的红外光谱，这揭示了79和104公里的$^{-1}$之间的预计旋转速度的快速旋转。我们比较近红外光谱光球模型，以确定对象的基本参数和径向速度。我们发现，赤道旋转速度为所有三个对象是$\gtrsim$ 100公里秒$^{-1}$。这里报道的三个L和T矮星是迄今为止已知的旋转最快的，可能是最扁的超冷矮星。相应地，这三个都是寻找极光无线电发射和净光学/红外偏振的绝佳候选者。在撰写本文时，已经测量了78个L型、T型和Y型矮星的自转周期。最短自转周期在1小时附近的聚集表明棕矮星不太可能自转得更快。
英文摘要：
We present the discovery of rapid photometric variability in three ultra-cool dwarfs from long-duration monitoring with the Spitzer Space Telescope. The T7, L3.5, and L8 dwarfs have the shortest photometric periods known to date: ${1.080}^{+0.004}_{-0.005}$ h, ${1.14}^{+0.03}_{-0.01}$ h, and ${1.23}^{+0.01}_{-0.01}$ h, respectively. We confirm the rapid rotation through moderate-resolution infrared spectroscopy, which reveals projected rotational velocities between 79 and 104 km s$^{-1}$. We compare the near-infrared spectra to photospheric models to determine the objects' fundamental parameters and radial velocities. We find that the equatorial rotational velocities for all three objects are $\gtrsim$100 km s$^{-1}$. The three L and T dwarfs reported here are the most rapidly spinning and likely the most oblate field ultra-cool dwarfs known to date. Correspondingly, all three are excellent candidates for seeking auroral radio emission and net optical/infrared polarization. As of this writing, 78 L-, T-, and Y-dwarf rotation periods have now been measured. The clustering of the shortest rotation periods near 1 h suggests that brown dwarfs are unlikely to spin much faster.
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