Optical linear polarization in ultra cool dwarfs: A tool to probe dust in the ultra cool dwarf atmospheres

TL;DR

This study measures optical linear polarization in ultra cool dwarfs to investigate dust scattering and atmospheric properties, confirming theoretical predictions and revealing potential variability and debris disks.

Contribution

It provides new polarization measurements in R and I bands for ultra cool dwarfs, supporting dust scattering models and suggesting atmospheric variability and debris disks.

Findings

Higher polarization in R band compared to I band in 3/4 dwarfs

Evidence of polarization variability indicating dust cloud dynamics

Possible detection of a cold debris disk around one dwarf

Abstract

Aims.Recent studies have detected linear polarization in L dwarfs in the optical I band. Theoretical models have been developed to explain this polarization. These models predict higher polarization at shorter wavelengths. We discuss the polarization in the R and I band of 4 ultra cool dwarfs. Methods.We report linear polarization measurements of 4 ultra cool dwarfs in the R and I bands using the Intermediate dispersion Spectrograph and Imaging System (ISIS) mounted on the 4.2m William Herschel Telescope (WHT). Results.As predicted by theoretical models, we find a higher degree of polarization in the R band when compared to polarization in the I band for 3/4 of these ultra cool dwarfs. This suggests that dust scattering asymmetry is caused by oblateness >.We also show how these measurements fit the theoretical models. A case for variability of linear polarization is found, which suggests the presence of randomly distributed dust clouds. We also discuss one case for the presence of a cold debris disk.