Discovery of the Widest Very Low Mass Field Binary

Abstract

We present the discovery of the widest (~6700 AU) very low mass field binary to date, found in a proper motion cross-match of the Sloan Digital Sky Survey and the Two Micron All Sky Survey. Our follow-up J-band imaging provides a 10-year baseline for measuring proper motions. Consequently, we are able to confirm the common proper motion of the pair to within 10 mas, implying a 99.5% probability of their physical association. Near infrared spectra of the components indicate spectral types of M6+/-1 and M7+/-1. The system resides at a spectroscopic distance of 105+/-13 pc and has an angular separation of 63.38+/-0.05 arcsec. We have used evolutionary models to infer component masses of 0.105^{+0.029}_{-0.017} M_sun and 0.091^{+0.010}_{-0.007} Msun. The large separation and low binding energy of this system can provide constraints for formation models of very low mass stars.