On the Radii of Brown Dwarfs Measured with AKARI Near-Infrared Spectroscopy

We derive the radii of 16 brown dwarfs observed by AKARI using their parallaxes and the ratios of observed to model fluxes. We find that the brown dwarf radius ranges between 0.64-1.13 RJ with an average radius of 0.83 RJ. We find a trend in the relation between radii and Teff; the radius is at a minimum at Teff~1600 K, which corresponds to the spectral types of mid-to late-L. The result is interpreted by a combination of radius-mass and radius-age relations that are theoretically expected for brown dwarfs older than 10^8 yr.