We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hr: K2-22b. The highly variable transit depths, ranging from ∼0% to 1.3%, are suggestive of a planet that is disintegrating via the emission of dusty effluents. We characterize the host star as an M-dwarf with T eff ; 3800 K. We have obtained ground-based transit measurements with several 1-m class telescopes and with the GTC. These observations (1) improve the transit ephemeris; (2) confirm the variable nature of the transit depths; (3) indicate variations in the transit shapes; and (4) demonstrate clearly that at least on one occasion the transit depths were significantly wavelength dependent. The latter three effects tend to indicate extinction of starlight by dust rather than by any combination of solid bodies. The K2 observations yield a folded light curve with lower time resolution but with substantially better statistical precision compared with the ground-based observations. We detect a significant "bump" just after the transit egress, and a less significant bump just prior to transit ingress. We interpret these bumps in the context of a planet that is not only likely streaming a dust tail behind it, but also has a more prominent leading dust trail that precedes it. This effect is modeled in terms of dust grains that can escape to beyond the planetʼs Hill sphere and effectively undergo "Roche lobe overflow," even though the planetʼs surface is likely underfilling its Roche lobe by a factor of 2.
Aims. We aim to extend our current observational understanding of the integrated planet Earth spectropolarimetry from the optical to the near-infrared wavelengths. Major biomarkers like O 2 and water vapor are strong flux absorbents in the Earth's atmosphere, and some linear polarization of the reflected stellar light is expected to occur at these wavelengths. Methods. Simultaneous optical (0.4−0.9 μm) and near-infrared (0.9−2.3 μm) linear spectropolarimetric data of the earthshine were acquired by observing the nightside of the waxing Moon. The data have sufficient spectral resolution (2.51 nm in the optical, and 1.83 and 2.91 nm in the near-infrared) to resolve major molecular species present in the Earth's atmosphere. Results. We find the highest values of linear polarization (≥10%) at the bluest wavelengths, which agrees with other studies. Linear polarization intensity steadily decreases toward red wavelengths reaching a nearly flat value beyond ∼0.8 μm. In the near-infrared, we measured a polarization degree of ∼4.5 % for the continuum. We report the detection of molecular features due to O 2 at 0.760, 1.25 μm, and H 2 O at 0.653-0.725 μm, 0.780-0.825 μm, 0.93, and 1.12 μm in the spectropolarimetric data, and most of them show high linear polarimetry degrees above the continuum. In particular, the broad H 2 O 1.12 μm band displays a polarimetric intensity as high as that of the blue optical. These features may become a powerful tool for characterizing Earth-like planets in polarized light.
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.
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