Weather on Other Worlds. V. The Three Most Rapidly Rotating Ultra-cool Dwarfs
Abstract
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: ${1.080}_{-0.005}^{+0.004}$ hr, ${1.14}_{-0.01}^{+0.03}$ hr, and ${1.23}_{-0.01}^{+0.01}$ 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.
- Publication:
-
The Astronomical Journal
- Pub Date:
- May 2021
- DOI:
- 10.3847/1538-3881/abeb67
- arXiv:
- arXiv:2103.01990
- Bibcode:
- 2021AJ....161..224T
- Keywords:
-
- Brown dwarfs;
- Stellar rotation;
- Variable stars;
- Infrared photometry;
- Spectroscopy;
- 185;
- 1629;
- 1761;
- 792;
- 1558;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 35 pages, 13 figures, 6 tables, accepted for publication in the Astronomical Journal, typos corrected in updated version
