The missing M dwarfs

We present evidence which indicates the luminosity functions of star-forming regions, open star clusters and the field dips between spectral types M7 and M8. We attribute this to a sharp local drop in the luminosity–mass relation and speculate that this is caused by the beginning of dust formation in the atmospheres of objects in this effective temperature regime. This effect is not predicted by the current generation of low-mass stellar/substellar evolutionary models. If our interpretation is correct then this result has important implications for investigations concerned with the mass functions of star-forming regions and young open star clusters. For example, it suggests that some brown dwarfs have higher masses than previously thought.