New light on faint stars - V. Infrared photometry and the H-R diagram for very low mass dwarfs

We present new optical and infrared photometry of a large sample of very low mass dwarfs, including three of the five intrinsically faintest stars yet discovered. These data are used to recalibrate the stellar effective temperature sequence below 3500 K, and to reinvestigate the stellar population structure in the H–R (log TEFF versus log luminosity) and J–H/H–K diagrams. All known low mass dwarfs lie near the expected hydrogen burning main sequence in the H–R diagram. We find no evidence for any representatives of a ‘black dwarf’ population, with masses below the theoretical hydrogen burning limit. The dispersion in the infrared two-colour diagram is dominated by metallicity variations, and is only weakly correlated with stellar kinematic populations.