# Testing the existence of optical linear polarization in young brown dwarfs

## TL;DR

This study investigates optical linear polarization in young brown dwarfs to understand atmospheric condensates, finding generally low polarization levels but detecting significant polarization in one M6 dwarf, supporting models linking oblateness and polarization.

## Contribution

First measurement of optical linear polarization in a sample of young brown dwarfs, testing model predictions about atmospheric condensates and oblateness effects.

## Key findings

- All targets have polarization below 0.69% in I-band and 1.0% in R-band.
- Significant polarization detected in one M6 dwarf with 0.81% in R-band.
- Results support the link between oblateness and polarization in young brown dwarfs.

## Abstract

Linear polarization can be used as a probe of the existence of atmospheric condensates in ultracool dwarfs. Models predict that the observed linear polarization increases withthe degree of oblateness, which is inversely proportional to the surface gravity. We aimed to test the existence of optical linear polarization in a sample of bright young brown dwarfs, with spectral types between M6 and L2, observable from the Calar Alto Observatory, and cataloged previously as low gravity objects using spectroscopy. Linear polarimetric images were collected in I and R-band using CAFOS at the 2.2 m telescope in Calar Alto Observatory (Spain). The flux ratio method was employed to determine the linear polarization degrees. With a confidence of 3$\sigma$, our data indicate that all targets have a linear polarimetry degree in average below 0.69% in the I-band, and below 1.0% in the R-band, at the time they were observed. We detected significant (i.e. P/$\sigma$ $\le$ 3) linear polarization for the young M6 dwarf 2MASS J04221413+1530525 in the R-band, with a degree of $\mathrm{p^{*}}$ = 0.81 $\pm$ 0.17 %.