Published February 24, 2021 | Version v1
Poster Open

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

  • 1. University of Western Ontario
  • 2. Institute for Astronomy, University of Hawaii
  • 3. European Southern Observatory
  • 4. Planétarium Rio Tinto Alcan
  • 5. University of California, San Diego
  • 6. NASA Ames Research Center
  • 7. Steward Observatory, The University of Arizona
  • 8. George Mason University


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.



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