February 24, 2021 Poster Open Access

Weather on Other Worlds. V. The Three Most Rapidly Rotating Ultra-Cool Dwarfs

Tannock, Megan E.; Metchev, Stanimir; Heinze, Aren; Miles-Páez, Paulo; Gagné, Jonathan; Burgasser, Adam; Marley, Mark S.; Apai, Dániel; Suarez, Genaro; Plavchan, Peter

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 that 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.