Three Wide Separation L-dwarf Companions from the Two Micron All Sky Survey: Gl 337c, Gl 618.1b, and Hd 89744b

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 (∆ ≥ 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 HD89744Ab. 1. introduction The study of binary and multiple systems in the local neighborhood is important for several reasons. It is desirable to have an accurate accounting of stellar systems in the local neighborhood. Improving the statistics of binary primary masses, system mass fractions, orbital separations, and eccentricities are crucial for refining stellar and planetary formation theories. Also, studying wide separation systems in particular gives insight into their dynamic stability with time as a function of orbital separation and mass fraction (and hence binding energy) against disruptive events such as close approaches to giant molecular clouds, stars, and the gravitational potential of the inner Galaxy. In this paper we present three wide separation L-dwarf companions to nearby stars. One companion has an apparent separation (∆) of 100 AU < ∆ < 1000 AU, and two have ∆ > 1000 AU. These discoveries, along with similar companions previously reported, highlight the success in searching new portions of binary system phase space (i.e. wide separations) by surveys such as Two Micron All Skyveys' sensitivities and large areal coverages allow for very low-mass (VLM) stars and brown dwarf companions to be found at separations ∆ > 100 AU. 8 The new detections will in turn improve the statistics of systems with mass ratios (q) far from unity. 9 For instance, the low-mass companions already discovered show that the 'brown dwarf desert' at close separation (< 1 % of FGKM main sequence primaries have brown dwarf companions at ∆ < 3 AU; Marcy & Butler (2000)) …