Investigating the magnetism of brown dwarfs

TL;DR

This study models the spectra of two brown dwarfs to infer their magnetic fields, providing upper limits and preliminary evidence for kiloGauss magnetic strengths consistent with other observational data.

Contribution

First modeling of brown dwarf spectra including polarimetric signals to estimate magnetic field strengths from spectropolarimetric data.

Findings

Preliminary evidence for kG magnetic fields in both brown dwarfs.

Upper limits on magnetic field strengths based on intensity spectra.

Agreement with magnetic field estimates from other observational methods.

Abstract

We model the spectra of two brown dwarfs observed with the low resolution spectropolarimeter LRIS (Keck observatory) during several rotational phases in order to infer their magnetic properties. The spectra modeled include the intensity signal (Stokes I/Ic) as well as the polarimetric signals (Stokes Q/Ic, U/Ic, and V/Ic), all coming from the 0-0 vibrational band of the CrH molecule at approx. 8610 A. In order to model the Stokes profiles, we solve a set of the radiative transfer equations for the CrH transitions in the presence of an external magnetic field. We present the upper limits for the magnetic field strengths for the objects observed, based on the modeling of the intensity signal I/Ic and the signal-to-noise information only. The proper modeling of the polarimetric signals, that requires more careful data reduction, is underway. Nevertheless, our preliminary results show a hint for kG magnetic fields for both brown dwarfs, that is in a good agreement with the result obtained from the simultaneous radio, H{\alpha} and X-Ray observations of one another radio pulsating brown dwarf.