tokens: these models demonstrate that banded clouds are easily able to explain the level of polarization measured in Luhman 16A. Considering the disagreement between the measurements and the homogeneous oblate polarization model, we conclude that cloud banding is the dominant source of the measured polarization in Luhman 16A. For Luhman 16B, we can neither rule out nor confirm the presence of banded clouds; the measurements could be explained as due to oblateness alone with clouds thinner than in the f sed = 1 models, or by a combination of oblateness and banded clouds. Although we model the bands and fit the polarization as constant over longitude and time, there is the possibility of variability with amplitudes below our sensitivity limits. Indeed, the bands of Jupiter display variability, yet the bulk features remain relatively constant over time (Ge et al. 2019 ). Similar variability superimposed on the bands discovered here may account for the previously detected photometric variability seen in Luhman 16A. 4.3. Spin Axis Orientations from the Angle of Linear Polarization The angle of polarization for Luhman 16A and B differs by ∼105° (or equivalently, ∼75°, because of a 180° degeneracy in the definition of the angle of polarization). For each object, the angle of polarization could be aligned either parallel or perpendicular to the position angle of the projected on-sky spin axis, as discussed in Section 4.2 . The misalignment of the angle of polarization immediately suggests a misalignment of the two components’ spin axes of either ∼15° or ∼75°, depending on the source of polarization of Luhman 16B. Neither component has an angle of polarization aligned parallel or perpendicular to the longitude of the ascending node of the binary orbit, Ω = 13012 ± 012 (Garcia et al. 2017 ). Luhman 16A’s polarization is at best ∼20° misaligned, and Luhman 16B is ∼40°–60°, indicating that neither object has a spin axis aligned with the orbital plane, regardless of the oblateness or banded interpretation. The misalignment may imply that the two objects did not form alone together within the same disk, but instead may have instead experienced a more raucous dynamical history such as having originally been formed in a triple system (Reipurth Mikkola 2015 ). To the best of the authors’ knowledge, this is the first measurement of the projected spin axis for any brown dwarf (albeit with a 90° degeneracy). Given the low-S/N detection of Luhman 16B, we consider any interpretation of its position angle to be tentative. 5. Total Intensity Variability Interpretation We were unable to measure absolute photometric variability, but the flux ratio of the two objects exhibits quasi-periodic variations, with a period of 1.64 hr. We attribute this signal to Luhman 16B alone ( H -band variability has never been detected in A; e.g., Biller et al. 2013 ; Buenzli et al. 2015b ) and suggest that it may represent a similar three-band scenario to that inferred for other L/T
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