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: hr, hr, and hr, 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 ≳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 hr suggests that brown dwarfs are unlikely to spin much faster.

我们展示了通过斯皮策太空望远镜长期监测发现的三个超冷矮星的快速光度变化。T7、L3.5 和 L8 矮星具有迄今为止已知的最短光度周期：分别为hr、hr 和hr。我们通过中等分辨率的红外光谱证实了快速旋转，它揭示了 79 到 104 km s ^-1之间的预计旋转速度。我们将近红外光谱与光球模型进行比较，以确定物体的基本参数和径向速度。我们发现所有三个物体的赤道旋转速度都是 ≳100 km s ⁻¹. 这里报告的三个 L 和 T 矮星是迄今为止已知的旋转速度最快的，也可能是最扁圆的超冷矮星。相应地，这三者都是寻求极光无线电发射和净光/红外偏振的绝佳候选者。在撰写本文时，现已测量了 78 个 L-、T- 和 Y-矮星自转周期。接近 1 小时的最短自转周期的聚集表明褐矮星不太可能旋转得更快。