Program: GN-2009B-Q-10

We propose to obtain resolved JHK photometry of 27 Very Low Mass (VLM) binaries using NIRI+ALTAIR on Gemini North. 15 targets have large astrometric perturbations indicative of a companion. 9 targets were resolved with HST/FGS as binaries, but do not have resolved infrared photometry. Obtaining resolved JHK photometry is crucial for a physical characterization of these objects, as VLM stars have their peak flux in the near infrared. JHK photometry is often used as the starting point for determining bolometric luminosities for VLM stars. Due to the large amount of near infrared data available from the 2MASS survey, the near infrared color space is currently the most widely populated color space when studying low mass stars and brown dwarfs. 2 targets were marginally resolved in an HST/NICMOS search for close companions to nearby stars and again lack photometry. One last target with known trigonometric parallax is over-luminous in a manner consistent with it being an unresolved binary with nearly equal fluxes from both components. Much work has been done in the field of Very Low Mass stars during the past decade, but the fundamental question of where the exact boundary between stellar and sub-stellar objects lies is still largely unanswered. This is due to the lack of reliable observational tests that discriminate between the most massive brown dwarfs and the least massive stars. Characterizing objects near this boundary is a fundamental aspect of the PI's doctoral thesis. We will use the resolved infrared photometry to place these Very Low Mass objects in color-magnitude diagrams and start mapping orbits, thus further populating the Mass-Luminosity Relation in this critical and as of yet sparsely populated mass range.