Three Wide-Separation L Dwarf Companions from the Two Micron All Sky Survey: Gliese 337C, Gliese 618.1B, and HD 89744B

Abstract

We present two confirmed wide-separation L dwarf common proper-motion companions to nearby stars and one candidate identified from the Two Micron All Sky Survey. Spectral types from optical spectroscopy are L0 V, L2.5 V, and L8 V. Near-infrared, low-resolution spectra of the companions are provided, as well as a grid of known objects spanning M6 V-T dwarfs to support spectral type assignment for these and future L dwarfs in the z'JHK bands. Using published measurements, we estimate ages of the companions from physical properties of the primaries. These crude ages allow us to estimate companion masses using theoretical low-mass star and brown dwarf evolutionary models. The new L dwarfs in this paper bring the number of known wide-binary (Δ>=100 AU) L dwarf companions of nearby stars to nine. One of the L dwarfs is a wide-separation companion to the F7 IV-V+extrasolar planet system HD 89744Ab. Portions of the data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Observations at the Palomar Observatory were made as part of a continuing collaboration between the California Institute of Technology and Cornell University. The 60 inch telescope at Palomar Mountain is jointly owned by the California Institute of Technology and the Carnegie Institution of Washington.