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

New optical and infrared photometry of a large sample of very low mass dwarfs, including three of the five intrinsically faintest stars yet discovered, are presented. 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 T(EFF) 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. No evidence is found for any representatives of a 'black dwarf' population, with masses below the theoretical hydrogen burning limit. The dispersion in the infrared two-color diagram is dominated by metallicity variations, and is only weakly correlated with stellar kinematic populations.