Latest News on the Physics of Brown Dwarfs

Abstract

The physics of brown dwarfs has continuously improved since the discovery of these astrophysical bodies. The first important developments were devoted to the description of their mechanical structure, with the derivation of an appropriate equation of state, and the modelling of their atmosphere characterised by strong molecular absorption. New challenges are arising with progress in observational techniques which provide data of unprecedented accuracy. The goal of this chapter is to describe some of the current challenges for the theory of brown dwarfs. Those challenges concerns atmospheric dust and cloud, non-equilibrium atmospheric chemistry, the effect of rotation and magnetic fields on internal structure and the very early phases of evolution characterised by accretion processes. The field remains lively as more and more high quality observational data become available and because of increasing discoveries of exoplanets. Indeed, many physical properties of giant exoplanets can be described by the same theory as brown dwarfs, as described in this chapter.

SOPHIE velocimetry ofKeplertransit candidates

“…The position of KOI-686 b in the mass-radius relation agrees with theoretical expectations based on the isochrones of Baraffe et al (2003). However, the more recent, and more complete models by the Dartmouth group (Feiden & Chaboyer 2013, 2014 failed to reproduce the observations, and give a radius anomaly of around 6%, not unlike other objects in the literature, such as CM Draconis (Morales et al 2009;Terrien et al 2012;see also Feiden & Chaboyer 2012). In addition, KOI-189 b might also be a high-mass brown dwarf, since the H-burning limit of ∼72 M Jup is contained in the 95%-HDI of the mass posterior distribution.…”

“…The models by Baraffe et al (2003) predict a radius in agreement with observations: a consistent radius value is within the 80%-HDI of the posterior radius anomaly for both the 1 Gyr and 5 Gyr isochrones. In this case, a comparison with the newest Dartmouth isochrones (Feiden & Chaboyer 2013, 2014, which include various effects due to magnetic fields, is also possible. Using the web-based interpolation tool provided by Dartmouth 3 , we computed the isochrones for the metallicity values at either end of the 95%-HDI (−0.34, 0.22), which are plotted in Fig.…”

“…The observed mass-radius relation of low-mass stars is still poorly understood (see Baraffe 2014, for a recent review). The observed radii of low-mass stars are between 5% and 10% larger than predicted by models (e.g., Morales et al 2010).…”

Early Results From VLT Sphere: Long-Slit Spectroscopy of 2mass 0122–2439 B, a Young Companion Near the Deuterium Burning Limit

“…The study of objects with masses and temperatures near the transition between the L and T spectral types, the so-called "L/T transition objects," has emerged as one of the most interesting and perplexing phenomena of substellar physics (Barman et al 2011;Baraffe 2014). Indeed, ongoing observations of substellar objects continue to confirm early indications that spectral types for L/T transition objects have a very strong dependence on surface gravity (e.g., Metchev & Hillenbrand 2006;Liu et al 2013b).…”

Search for light curve modulations amongKeplercandidates

“…The three systems studied here (together with a few others) fill a void region in the diagram, part of the so-called brown-dwarf desert. The derived properties of these low-mass companions can feed formation theories and interior models (Baraffe 2014) of objects of this type, since very few of them are known.…”