Near-infrared Linear Polarization of Ultracool Dwarfs

TL;DR

This study measures near-infrared linear polarization in ultracool dwarfs, finding one strongly polarized object likely due to a surrounding disk, providing insights into dust and atmospheric properties.

Contribution

First near-infrared polarimetric measurements of ultracool dwarfs, revealing polarization levels and potential disk presence, enhancing understanding of dust and atmospheric phenomena.

Findings

Most targets show polarization below 0.9%.

One L0 dwarf exhibits ~3% polarization, likely from a disk.

The polarized source is a prime candidate for direct disk detection.

Abstract

We report on near-infrared J- and H-band linear polarimetric photometry of eight ultracool dwarfs (two late-M, five L0-L7.5, and one T2.5) with known evidence for photometric variability due to dust clouds, anomalous red infrared colors, or low-gravity atmospheres. The polarimetric data were acquired with the LIRIS instrument on the William Herschel Telescope. We also provide mid-infrared photometry in the interval 3.4-24 micron for some targets obtained with Spitzer and WISE, which has allowed us to confirm the peculiar red colors of five sources in the sample. We can impose modest upper limits of 0.9% and 1.8% on the linear polarization degree for seven targets with a confidence of 99%. Only one source, 2MAS, J02411151-0326587 (L0), appears to be strongly polarized (P ~ 3%) in the J-band with a significance level of P/sigma_P ~ 10. The likely origin of its linearly polarized light and rather red infrared colors may reside in a surrounding disk with an asymmetric distribution of grains. Given its proximity (66 +/- 8 pc), this object becomes an excellent target for the direct detection of the disk.