Luminosities and temperatures of M dwarf stars from infrared photometry

Abstract

Broad-band infrared photometry at 1.65, 2.2, and 3.5 /x has yielded accurate bolometric magnitudes for a large number of M type dwarf stars. The intrinsic dispersion in these stars is found to be ~±0.4 mag in M b vs V-K and M b vs R-I magnitude-color diagrams. This dispersion in the lower main sequence may be the result of differential blanketing in the UBVRI filter bands and, thus, there may not be a unique main sequence for the intrinsically faint M dwarfs. Analysis shows that one parameter is sufficient to describe the blanketing in all of the UBVRI bands for all types of M dwarfs. In general, late M dwarfs seem to have lower effective temperatures than are predicted by theoretical models. M dwarfs that belong to the halo population on the basis of their large space motions tend to be subluminous in Af 6 vs V-K and M b vs R-I magnitude-color diagrams although they have a large scatter. In these diagrams, stars with hydrogen emission lines average-0.3 bolometric magnitude brighter than M dwarfs without any emission lines. The data for late dwarfs with known masses imply the empirical mass-luminosity relation: L fLQcc(M /MQ) 22±02 for stars fainter than M b =7.5. INTRODUCTION