The WIRC+Pol Brown Dwarf Survey: A J -band Polarimetric Survey of 22 Brown Dwarfs

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Abstract
We present a near-infrared spectropolarimetric survey of brown dwarfs conducted with the WIRC+Pol instrument on the Palomar 200 inch Hale Telescope. The primary survey goal was to investigate the presence of polarization signatures arising from cloudy atmospheres in these objects, with possible asymmetries indicating patchy cloud distributions. Our sample includes 22 brown dwarfs spanning M6 to T2 spectral types, a crucial phase in the evolution of substellar objects characterized by suspected drastic changes in atmospheric composition and structure. We find that only three of the brown dwarfs in our sample show a detectable polarization signal: CFHT BD Tau 4 and 2MASS J04221413+1530525, which are both located in or near molecular clouds, complicating interpretation of the polarimetric signal due to likely contamination from interstellar dust scattering; and 2MASS J15074769-1627386, which is a nearby L dwarf with previously confirmed photometric variability and measured optical polarization, here with its first measured near-infrared polarization. For this target, we rule out interstellar polarization and rotationally induced oblateness as possible causes of the measured polarization, potentially suggesting atmospheric asymmetries as the culprit.
Funding Information
  • National Science Foundation (AAG-1816341)

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