NLTT5306B: an inflated, weakly irradiated brown dwarf

TL;DR

This study presents infrared observations of the brown dwarf NLTT5306B, revealing it as an inflated, weakly irradiated L5 type object with minimal temperature variation across its surface.

Contribution

It provides the first detailed infrared characterization of NLTT5306B, highlighting its inflation despite low irradiation and exploring potential mechanisms behind this inflation.

Findings

NLTT5306B is an L5 brown dwarf with an inflated radius.

Minimal day-night temperature difference observed.

Inflation mechanisms may include magnetic interactions or thick clouds.

Abstract

We present Spitzer observations at 3.6 and 4.5 microns and a near-infrared IRTF SpeX spectrum of the irradiated brown dwarf NLTT5306B. We determine that the brown dwarf has a spectral type of L5 and is likely inflated, despite the low effective temperature of the white dwarf primary star. We calculate brightness temperatures in the Spitzer wavebands for both the model radius, and Roche Lobe radius of the brown dwarf, and conclude that there is very little day-night side temperature difference. We discuss various mechanisms by which NLTT5306B may be inflated, and determine that while low mass brown dwarfs (M<35 MJup) are easily inflated by irradiation from their host star, very few higher mass brown dwarfs are inflated. The higher mass brown dwarfs that are inflated may be inflated by magnetic interactions or may have thicker clouds.