Program: GN-2008A-Q-80

We have performed a multi-epoch search for co-moving cool dwarf companions to known high proper motion stars using data from the 2MASS, SDSS, and SIMP near-infrared surveys. We have identified 29 co-moving candidate companions, 14 of which are currently followed-up through a DD proposal at GS, we propose to observe the remaining 15 companions. The estimated spectral types of these companions are in the range M7-L4 and their estimated physical separations are in the range 300-12 000 AU. These systems, which fall in a sparsely populated region of the mass/separation diagram of known binaries, have a strong bearing on low-mass star formation models. We request 22 hours to obtain GMOS spectroscopy of 15 systems to constrain their physical properties. Namely, these observations will allow us to (1) determine a precise spectral type/effective temperature for each component, (2) establish more precise photometric distances, (3) constrain the age of the systems, and (4) possibly uncover mildly over-luminous secondaries that might be tight binaries themselves. These new companions furher constitute benchmark objects for testing and calibrating low-mass star/brown dwarf evolution models, especially if youth indicators are detected in their spectrum. Finally, any secondary found to be a tight binary would offer the possibility of a dynamical mass measurement within a few years.