Cool Companions to White Dwarfs from 2MASS

Abstract

We present near-infrared magnitudes for white dwarfs selected from the catalog of McCook & Sion that are contained in the 2 Micron All Sky Survey Second Incremental Data Release. We show that the loci of single WDs and WD + red dwarf binaries occupy distinct regions of the near-IR color-color diagram. Using observational near-IR data for WDs and M—L dwarfs, we have compared a sample of simulated WD + red dwarf binaries with our 2MASS data. The colors of the simulated binaries are dominated by the low mass companion through the late-M to early-L spectral types. For later spectral types of the companion, however, the colors of unresolved binaries become progressively bluer. Binaries containing the lowest mass companions will be difficult to distinguish from single WDs solely on the basis of their near-IR colors.